Effects of a warmer climate on societies and ecosystems

Effects on society

We currently officially live in the Holocene age (though, as discussed in the chapter, it

really is the Anthropocene Age), and we have lived in settlements only since the end of

the Younger Dryas, around 12,000 years ago. The hunter-gatherer Natufians of southwest

Asia abandoned seasonal hunting-gathering and adopted subsistence agriculture, also

12,000 years ago. Coincidence? Most experts think not.(362) The Natufian open parkland

of the Younger Dryas there was succeeded by agriculture because wild harvests

decreased.(363)

There was a two-century drought in the Mideast around 6400 BC, evidence of an abrupt

climatic change that took place. Agricultural towns were abandoned, then after the

drought ended, Mesopotamian settlements occurred.(362-364) Dramatic records on wind-

blown dust were found.(363,365) A shorter Mideast drought around 3000 BC caused the

Urik culture to disappear.(362) Returning wet conditions coincided with the rise of the

Akkadian Empire,(365) the Egyptian Old Kingdom, and the Harappans of the Indus

Valley.(362,364) These collapsed in the wake of a 30% drop in rainfall that stretched from

the Aegean Sea to the Indus Valley.(362)

In the Americas, the rise of civilization coincided with the advent of the El Niño around

5,800 years ago. The change in climate allowed gathering of sufficient resources to sustain

temple-building and other civilized activities.(364) A 30-year drought-and-flood sequence

in the sixth century damaged Moche civilization.(362,363) The Andean Tiwanaku

civilization collapsed amid drought in the tenth century, a drought recorded in glacier

cores.. The Mayan civilization also collapsed due to a severe drought in the ninth

century.(362,365) This same change spread deserts in North America.(366) A wet period

coincident with the beginnings of corn cultivation occurred around 2,800 years ago.(366) In

the wet period 750 to 900 AD, the Pueblo culture flourished in the American

southwest.(366) The Mesa Verde Pueblos and the Anasazi civilization disappeared

because of drought, as we pointed out early in Chapter 14.(363,366,367)

Also 5,800 years ago, Chinese civilization appeared due to the same climate changes that

supported South American civilizations. The Japanese Middle Jomon Period runs from

3800 BC to 1200 BC, and there are more significant architectural ruins than

previously.(364)

Fig. E17.4.1 The dust bowl produced towns such as Liberal, Kansas in 1936.(U.S. Resettlement Administration)

In more recent times, the “Dust Bowl” droughts of the 1930s led to massive migration

from Oklahoma to California. That drought was due to a Pacific temperature anomaly,

and similar evidence has been found of such droughts periodically in the climate

record.(368)

These were pikers. Megadroughts were characteristic before the 1600s, and we now know

from Virginia tree-ring data that the Roanoke Colony failed because it arrived just as an

extraordinary 800-year drought did, one that affected the whole east but was particularly

severe near Roanoke.(363,369) The same lingering drought also made the Jamestown

settlers’ lives miserable (when they kept them at all).(369) They arrived in April 1607, a

year after the start of a drought that lasted until 1612 (the seven driest years in the

record). Drought killed not only because crops failed and animals became sick, but

because water quality is much lower during drought periods.(369)

Weather changes that affect people and other living things

People are subject to effects of weather more in some places than others. People tend to

be moving to the coasts, which are more prone to severe weather, and this is at least

partly responsible for the increased insurance payouts for disasters.(370) There are more

extreme weather events expected in the future warmer world.(370,371) Temperatures are

expected to be more extreme, there are going to be more droughts and more floods, and

more tropical storms (except China).(370,372) Obviously, insurance involves risk

assessment, and the coming future demands better analyses of risk.(371)

Water resources are already in perilously short supply in some locations (see Chs. 8, 9

and 18). Water stress will continue to increase. Reference 374 expects that rising

population pressure will cause more of a water problem than climate change. Also,

population relocations will stress water supplies.(373) However, here, too, more data are

needed.(374) One concern in regions near mountains is that with a smaller snowpack

expected, water transfers’ timing will change in ways that may be unhelpful to water

supply systems.

Obviously sea level rise will threaten small island states.(375,376) Sea level rise also

threatens coastal wetlands, and the coastal wetlands play a large role in fisheries (see

below).(80) This is a cause for concern. For further information, see Extension 17.5,

What does sea level rise mean?

Fig. E17.4.2 Annual global surface mean temperature anomalies 1880-2003 (baseline 1961-1990).(National Climatic Data Center/NESDIS/NOAA)

We have seen in Chapter 17 that the global temperature has been increasing. Figure

E17.4.2 shows the history of the land and ocean temperatures from 1880 to 2003 (see

Fig. 17.9 for the month-by-month global temperature change). The documented rise has

clearly caused changes, to be discussed below. Even with our greater knowledge of what is

happening to our planet and its social effects, there is no guarantee that the future world

will be better for people (especially for the world’s poor). However, even now,

smallholders all over the world can benefit from satellite observations that lead to better

forecasts.(377)

Fig. E17.4.3 Annual 2003 temperature anomalies. The larger the red dot, the greater the temperatureincrease above the longterm mean; the larger the blue dot, the greater the temperature decrease below thelongterm mean. Source: National Climatic Data Center/NESDIS/NOAA

A sense of how the world temperature is changing from the longterm mean is shown in

Fig. E17.4.3. The predominance of large red speckles show clearly how different the

world is becoming, and where in the world the changes are occurring. Note the large

number of large red dots near the poles (there are more observing stations near the north

pole).

Effects on health

The National Academy Committee on Climate, Ecosystems, Infectious Diseases, and

Human Health points out the obvious:(378) “Simple logic suggests that climate can affect

infectious disease patterns because disease agents (viruses, bacteria, and other parasites)

and their vectors (such as insects or rodents) are clearly sensitive to temperature,

moisture, and other ambient environmental conditions.” The Committee goes on to point

out how weather works hand in hand with disease, so that “mosquito-borne diseases such

as dengue, malaria, and yellow fever are associated with warm weather; influenza becomes

epidemic primarily during cool weather; meningitis is associated with dry environments;

and cryptosporidiosis outbreaks are associated with heavy rainfall.”(378) Ironically, both

floods and droughts favor waterborne illnesses (different ones, to be sure).(379)

Harvell et al. argue that the world is already laboring under the impact of pathogens

affecting humans and animals, and the warmer, the worse for us all. They cite changes in

corals and oysters, plant pathogens, insect fungal pathogens, and Rift Valley and dengue

fever. They “suggest several ways in which climate warming has altered and will alter

disease severity or prevalence. In the temperate zone, shorter, milder winters are expected

to increase disease spread. In tropical oceans, warmer summers may increase host

susceptibility through thermal stress.”(380)

While the health systems of developed countries will not be adversely affected to a great

extent by a warmer climate,(381) overall in the world, conditions will get substantially

worse.(375) Air quality in urban areas will suffer everywhere.(375)

Everyone agrees that there will be additional heat stress.(375,378,381,382) Many more

people in urban areas are expected to die, at least several hundred per year in the United

States alone.(375,381) Shanghai may have thousands more deaths per year than now.(381)

In a warmer world, it is predicted that around 700,000 avoidable premature deaths will

result from air pollution.(383) Reducing greenhouse gases will save lives disproportionally

in the less developed world.(383) The warmer winters will mean fewer people in the

temperate climates will die of pulmonary or cardiovascular disease in winter.(375,378,381-

384) There will be smaller releases of allergenic pollens (they do well in hot dry summers),

decreasing allergic response but a concomitant increase in breeding of house mites, with

more possibility of asthma and other bronchial problems.(382) Increased rainfall predicted

in various places will lead to better breeding conditions for rodents and increased risk of

diseases such as hantavirus.(375)

Cholera is a disease of long standing that affects the digestive system and can kill

quickly.(385) Cholera pandemics arose between 1817 to 1823, 1829 to 1851, 1852 to

1859, 1863 to 1879, 1881 to 1896, and 1899 to 1923. It was assumed that modern

hygiene would prevent further pandemics, but after a long pause, the current pandemic

began in 1961.(385) All appeared around coastlines, and are associated with water in some

way (see Chapter 26). Colwell points out how cholera in South America arose in 1991 in

the wake of an El Niño after a century of absence, causing at least 14,000 dead.(385) Sea

surface temperatures are associated with cholera outbreaks in the Bay of Bengal.(378,386)

While there is some controversy over whether the cholera outbreak was associated with

warmer waters, a warmer world will inevitably involve more such incidents.

Everyone agrees that a consequence of warming will be more water vapor in the air (air

holds about 6% more water for every 1 °C rise in temperature) that could lead to more

rainfall and more floods, as well as a more hospitable environment for breeding of

mosquitoes.(382,384) Rift Valley Fever can be predicted in advance from the rainfall, and

with satellite monitoring, outbreaks may be known five months before they occur.(384) A

similar thing could be done for malaria.(387)

If tropical climates spread from their current areas, it is possible that tropical diseases

could follow.(382) Malaria is responsible for about 1 million deaths a year, and infects

about twice as many people as live in the United States.(388) The African tropical

highlands could experience a great increase in malaria (the vectors are present locally) and

even in other places, the rapid pace of modern travel can bring infectious insects from

place to place.(382) (This happened with the West Nile virus, which appeared suddenly in

the United States in 1999).(379)

Conditions for the outbreak of malaria seem to be improving as the climate warms, since

Anopheles mosquitoes can cause sustained outbreaks of malaria only when the

temperature is greater than about 15 °C most of the time. (379) The time over which

malaria can infect people expands as warming occurs.(378,379,385,388) Many more local

outbreaks of malaria have been experienced. By the end of the twenty-first century, it is

expected that the range of these mosquitoes could expand from a region home to 45% of

the world population to one encompassing 60% of the world population.(379)

However, public health measures are important here, and if there is to be an increase in,

say, the United States, not only does the malaria have to get here and infect the

mosquitoes, they must breed (and have plenty of running water) and people have to be in

a place where they are exposed to the mosquitoes.(388,389) A more immediate risk of

catching these diseases is air travel by an infected person.(389) Screening and air

conditioning have decreased the exposure possibilities. Projections are that malaria will

not make much headway in advancing into developed countries.(388) For example, in

Britain, it is predicted that there will be an increase of 8% to 14% in local transmission

(there would be endemic malaria; at present, all British malaria cases are brought into the

country by infected people).(390)

Small et al. suggest that rainfall, not climate per se, is what is correlated with malaria

resurgence. To check this hypothesis will be difficult because of the awesome variability

in African weather.(391)

Hay et al. are more skeptical of warnings of the spread of malaria. They studied malaria in

Kenya over a century, and while malaria rates went up and down, climate didn’t change;

they conclude that other factors are more important. Their argument is interesting, but I

am skeptical because the climate must have varied in a study in order for the null

hypothesis to be tested.(392)

Aedes aegypti mosquitoes, which carry dengue fever, have recently been observed at

progressively higher altitudes in Central America.(379,382) Dengue fever affects 50 to 100

million people every year. It has spread to various locations worldwide, and, as yet, there

are no treatments available.(379) However, the difference in infection rates across the U.S.-

Mexican border shows that other factors can outweigh the natural levers tending to

increase risk.(375) A study of transmission of dengue fever and its association with El

Niño was carried out using data from 14 Pacific island nations. Positive correlations were

found for 10 countries between dengue and the Southern Oscillation Index, but there must

clearly be other factors involved as well, such as air travel, in the spread of dengue

fever.(393)

The National Academy Committee recommends several steps that we should develop an

“early warning system” Of course, as the Committee states, “investment in sophisticated

warning systems will be an effective use of resources only if a country has the capacity to

take meaningful actions in response to such warnings.”(378) Response is not enough, as

was found in the wake of the anthrax mailings of 2001 after the terrorist attacks on the

World Trade Center.(394) More active participation by citizens as well as professionals

can help us adjust. A major cause for concern is that new infectious diseases might

emerge, or evolve in unforeseeable ways.(378) As the Committee points out, “increasing

global travel could potentially influence the genetics of pathogenic microbes through

mutation and horizontal gene transfer, and could give rise to new interactions among hosts

and disease agents.”(378)

These effects work in the opposite way as well. Ruddiman (Reference 24) identified

increasing human effects on climate stretching back to around 8000 years ago. He argues

that the advent of the plague in Europe, killing about one-third of the population and

depopulating whole regions of Europe, reduced human effects on climate and so triggered

the Little Ice Age.

Farmers’ deaths would first reduce the carbon dioxide and methane emissions as farmland

sat idle and domestic animals died, and then, as idled farmland reverted to forest, carbon

storage would increase. If increasing carbon dioxide is responsible for the global

temperature rise, decreasing carbon dioxide should contrariwise be responsible for any

global temperature decrease. Ruddiman writes “A tentative assessment based on the

relative radiative forcings ... is that CO2 changes were on average comparable in

importance to solar and volcanic forcing in this cooling. Solar and volcanic forcing appear

to have been dominant at times such as the cooler decades near 1450 and 1825 AD.

Plague-driven CO2 decreases were probably most important just after 1350 AD and

between 1500 and 1750 AD.”(24)

Ruddiman estimated that this long-lasting effect of the plague would be to cause a

temperature decrease of about 0.17 °C.(24) This number agrees well with the temperature

reconstructions (Fig. 17.8) of Crowley and of Mann et al.(92,93) Voila! The Little Ice Age

had arrived, courtesy of human activities.

Effects on violence

In addition to the health problems that come as a result of warming (discussed above, and

Fig. E17.4.4), aggression rises when the temperature rises. People certainly do get cranky

when they are uncomfortable.(395) A psychologist has compared records of assaults and

homicide with outside summer temperature. He finds that 1 °C increase in average

temperature should result in about 9 more murders or assaults per 100,000 people

(around 24,000 additional murders and assaults for the U.S. Population).(396)

Fig. E17.4.4 The warmer world of the future.(German Climate Computing Center)

It has been suggested that it is not only hot spells that cause violent behavior to increase.

W. Behringer has suggested that the widespread adoption of burning witches for

practicing witchcraft arose out of frustration over the arrival of the Little Ice Age.(397) A

pope (Pope Innocence VIII) even accused witches of messing about with the weather in

the 1480s.(397) While the Little Ice Age lasted into the nineteenth century, witch-burning

eventually fell out of favor as a solution sooner.

Effects on ecosystems

Studies have begun to document the effects of climate change on the ecosystem. Refs.

223, 224, and 398 represent metastudies (studies of studies). All three have documented

effects on fauna as well as flora. Their conclusions are given in scientific language, but

strong for all that. Reference 398 says “it is clear that communities are already undergoing

reassembly that is attributable to climate change,” and points out that

As both ecological theory and conservation history have shown, the modern

landscape provides little flexibility for ecosystems to adjust to rapid

environmental changes. In contrast with historical responses and migration

processes, species in many areas today must move through a landscape that

human activity has rendered increasingly impassable. As a result of the

widespread loss and fragmentation of habitats, many areas which may become

climatically suitable with future warming are remote from current

distributions, and beyond the dispersal capacity of many species.

Consequently, species with low adaptability and/or dispersal capacity will be

caught by the dilemma of climate-forced range change and low likelihood of

finding distant habitats to colonize, ultimately resulting in increased

extinction rates.

Reference 223 says

These analyses reveal a consistent temperature-related shift, or “fingerprint,”

in species ranging from molluscs to mammals and from grasses to trees.

Indeed, more than 80% of the species that show changes are shifting in the

direction expected on the basis of known physiological constraints of species.

Consequently, the balance of evidence from these studies strongly suggests

that a significant impact of global warming is already discernible in animal and

plant populations.

Reference 224 says

A review of the literature reveals that the patterns that are being documented

in natural systems are surprisingly simple, despite the real and potential

complexity of biotic change. Change in any individual species, taxon or

geographic region may have a number of possible explanations, but the

overall effects of most confounding factors decline with increasing numbers

of species/systems studied. Similarly, uncertainty in climate attribution for

any particular study does not prevent the development of a global conclusion

on the basis of a cumulative synthesis. In particular, a clear pattern emerges

of temporal and spatial sign switches in biotic trends uniquely predicted as

responses to climate change. With 279 species (84% ) showing predicted sign

switches, this diagnostic indicator increases confidence in a climate change

fingerprint from either viewpoint.

Root et al. point out the four types of species trait response possible to a warmer

climate. They write “First, the density of species may change at given locations, and the

ranges of species may shift either poleward or up in elevation as species move to occupy

areas within their metabolic temperature tolerances. Second, because many natural history

traits of species are triggered by temperature-related cues, changes could occur in the

timing of events (phenology), such as migration, flowering or egg laying. Third, changes in

morphology, such as body size, and behaviour may occur. Fourth, genetic frequencies

may shift.”(223) Studies cited may focus on one or several of these indicators. Of course

these considerations would also apply in a change to a cooler climate (the first statement

would be the only one changed; if cooling took place, species would shift toward the

equator or downward on the mountain).

Mountaintops represent “islands” in terms of their ecological niches, and such

ecosystems have been extensively studied.(399,400) If the islands become smaller, the

number of species that can live there will decrease. According to Krajik, “[t]hese islands

are shrinking. The lowest elevation at which freezing occurs in mid-latitude mountains has

climbed 150 meters since 1970. (On average, each rise of 100 meters in altitude

corresponds to a 0.5 °C drop in mean temperature.) This appears to be hastening local

extinctions that have been proceeding slowly since the last glacial age.”

The extinction risk is heightened by the warming that is occurring. Thomas et al., using

the species-area relationship, predict that between 15 and 37 percent of species in their

study range (covering 20% of Earth’s surface) will become extinct by 2050.(401) For the

lowest range of global warming the study contemplated, from 0.8 °C to 1.7 °C, they

estimate an 18% probability of species extinction. At the highest range contemplated,

above 2 °C, they estimate a 35% probability for extinction. Thomas et al. conclude that

“anthropogenic climate warming at least ranks alongside other recognized threats to global

biodiversity. Contrary to previous projections, it is likely to be the greatest threat in

many if not most regions.” This is in contradiction to the result, for example, of Sala et al.,

which identified land-use changes as generally stronger than climate change in causing

extinctions (though recognizing that circumstances vary).(402)

Effects on plants

An experiment was undertaken over five years to determine the response of shortgrass in

a semiarid grassland of Colorado to heightened levels of CO2.(403) This is typical western

rangeland used for cattle grazing. The carbon dioxide was released by pipes near ground

level. Grass production of one type of grass was enhanced but it became less digestible.

The other grasses changed negligibly.(403) This result suggests that the increased carbon

dioxide concentration may lower the quality of available forage in the world’s grasslands.

We may be able to learn something about other effects on plants by looking at what

happened in the past.(404) It is clear that carbon dioxide had a great effect on plant

evolution. Plants could only develop their efficient leaves to tap carbon dioxide after CO2

levels fell low enough. The fossil record shows that there was “a 25-fold enlargement of

leaf blades in two phylogenetically independent clades as atmospheric CO2 levels fell

during the late Paleozoic.”(405)

Interglacial warming involved escape of species from refugia, and “weedy-type” species

have demonstrated an ability to colonize new ecosystems (see Extension 26.3, People

and plants and Extension 26.4, Interspecies competition, habitat, and ecosystem

services). Typical speeds of adaptation in the Quaternary were 150 km per century for

Scots pine (Pinus sylvestris) and today the species has a considerable diversity in its

ecosystems in different locations.(404) This is much greater movement than most other

species in the past, about 20 to 40 km per century, but they also now face a big problem

that did not exist in the Quaternary—the existence of cities and other barriers to

migration.(404) Model estimates imply that species will have to move 200 to 500 km per

century to be able to remain in comfortable climate ranges, which the authors of Reference

386 call “implausible.” Many species that have been moved intentionally did not set seed

as well as in their home range.(404) Reference 404 says that though there are fossil records

that show “examples of persistence through repeated periods of unfavorable climate,” ...

“the record of extirpations and extinctions suggests that limits to adaptation are greatest

during periods of rapid climate change.”

Half the global net primary production (NPP) occurs between the Equator and ± 22.5°,

most of it from the tropical evergreen forest; in simulations with increased CO2, NPP

decreases 8.9% to 20.6%.(406) Increases in CO2 do not guarantee plant growth; there are

limiting factors for growth.

Tundra has accumulated carbon since the end of the last ice age and currently tundra and

boreal forest soils hold an estimated 600 Gt of carbon.(246,318) There is concern that that

slowly accumulated carbon could come back out of the soils if warming persists and

intensifies. Such an increase in carbon dioxide would accelerate climate change. An

experiment that took place over a twenty-year period provides support for that

worry.(246,318) Initially, it was found that short-term stimulation by high CO2 over three

years with a 4 °C temperature increase leads to accumulation of carbon in tundra soil and

plants.(80,105,317)

The amount of carbon is related to nitrogen uptake. Unless there is an increase in nitrogen

mineralization as temperature increases, eventually there is a release of CO2. If nitrogen

mineralization increases, then CO2 would continue to be removed; but if leaching losses

are substantial, the tundra will become a CO2 source.(105,407) This occurs because the

ratio of carbon to nitrogen is much greater in plants than in the soil.(317) Over the longer

period, the results confounded the original expectations of Reference 317. Mack et al.

found that instead of stimulating decomposition and increasing nutrient availability, which

would have stimulated carbon storage, “results show the opposite response to increased

nutrient availability. Decomposition was stimulated more than plant production, leading

to a net loss of C from the ecosystem. Furthermore, the system had no capacity for net

retention of increased N inputs.”(317) As the researchers summarized the situation,

“annual aboveground plant production doubled during the experiment. Losses of carbon

and nitrogen from deep soil layers, however, were substantial and more than offset the

increased carbon and nitrogen storage in plant biomass and litter. Our study suggests that

projected release of soil nutrients associated with high-latitude warming may further

amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive

feedback to climate warming.”(317) As shrubs continue to take over former tundra, the

concern over this feedback is reasonable.

In an experiment, Hungate et al. found that initially, increased carbon dioxide in an oak

woodland led to increased growth and increased nitrogen fixation. By the end of the third

year of treatment (out of seven), the nitrogen fixation bonus had disappeared and the

enhanced concentration of carbon dioxide suppressed nitrogen fixation thereafter.(408) It

was found that this was due to lack of molybdenum, which is important to the function

of nitrogenase. Zavaleta et al. found the identical effect in a California grassland.(409)

An investigation of carbon storage in trees finds that trees store only about enough carbon

for four complete sets of leaves (four years’ worth).(410) Hoch et al.(410) say that their

data imply that there is not a lot of leeway for a further stimulation of

growth by ongoing atmospheric CO2 enrichment. The classical view that

deciduous trees rely more on C-reserves than evergreen trees, seems

unwarranted or has lost its justification due to the greater than 30% increase

in atmospheric CO2 concentrations over the last 150 years.

In a different experiment with trees on forest soils, neither trees on better nor those on

poorer soils gained any increment from increased carbon dioxide, but if the sites were

fertilized (with considerably more nitrogen than would be available from deposition in the

future), gains did occur.(411)

These results imply that the crop bonuses expected from the increase in CO2

concentration may never occur. This would make our meeting with the warmed future

climate even more ominous.

The world is warming and plants are responding. Alward et al. found that increased spring

minimum temperatures were correlated with reduction in the abundance of buffalo grass

(Bouteloua gracilis) and an increase in forbs.(412,413) Changes in temperature in an Arctic

system alter the composition of the plants, reducing the number of already less-abundant

species.(246) This could have the consequence that Arctic caribou herds will find less food

available.(413)

Plants are blooming earlier in spring (~16 days) and remaining longer in fall (~13 days) in

Mediterranean ecosystems.(414) British plants are blooming an average of 15 days

earlier.(415) Plants in Boston bloom 8 days earlier than in earlier times.(416) Many

examples of similar shifts (all in the same direction) may be found in the literature (see

Fig. E17.4.3). The growing season for the whole Northern Hemisphere is about a week

longer than it was in 1980.(414)

Fig. E17.4.3 The persistence of green plants in the northern hemisphere.(NASA Goddard Space Flight Center)

Enhanced photosynthesis in C3 plants have two effects. The stomata decrease in size by

~36% for doubled CO2, reducing water loss.(361,417,418) Also, the enzyme rubisco is more

active, so the amount of sucrose increases.(418) C4 plants are more efficient than C3 plants

at trapping CO2 with current concentrations. Under well-watered and fertilized

conditions, nearly all C3 species (including trees) show greater growth under increased

CO2 than C4 plants.(419,420) Typically, the C3 plants are the weeds, and C4 plants are the

grasses (and grains) so that increased CO2 will give weedy species an advantage.(421)

Waggoner and others have estimated that crop yields could increase 3 to 12% by this

mechanism,(422) although tests have shown that, while many plants grow faster in

increased CO2 environments, excessive CO2 may impair plant health (610 versus 340

µmol/mol [or parts per million]).(361,423) Starch disrupts the function of the plants.(423)

On the whole, however, photosynthesis appears to proceed best at CO2 concentrations

of around 600 µmol/mol, which is promising for future agriculture.

There are still problems that are bound to arise in natural ecosystems, which do not have

the human helping hand to plant new adapted species. FACE experiments in the Mojave

Desert with enriched CO2 concentrations (see Extension 17.7, Planting trees for a

description of the FACE experiments) showed that exotic grasses were likely to invade

the ecosystem.(424) The amount of biodiversity in a warmer world of 2100 is expected to

change Mediterranean and grassland ecosystems the most and temperate ecosystems the

least (at least partly because of the extensive changes wrought on the temperate

ecosystem in the past.(402)

In the drier U.S. Midwest, the growing season will be shortened by 10 days, droughts will

become more frequent, and irrigated farms will be in trouble, because they depend for

their irrigation water on the small difference between rains and evaporation that is stored

in geological formations.(361,422) Fossil water reservoirs there are already depleted. There

will certainly be squabbles over Colorado River water. The Colorado River Compact was

developed in the 1930s to allocate water among the various states. In the early twentieth

century, unprecedented water flow was available.(425) Now, more water from the

Colorado River has been allocated than actually flows in most parts. We have already

remarked that a 1 °C rise in temperature would reduce river flow by 25%; a 2 °C rise

would cause a 40% decrease in the flow.(422) The changes would demand radical

measures, such as the end of irrigated agriculture in the Colorado basin.(352,422)

There will be a major impact on the food chain. Jones et al. find that plants grown for

three generations under enhanced CO2 concentration experienced increased

photosynthesis, much of which was transported into the below-ground portion of the

plant. This increased dissolved organic carbon, which changed the fungal ecosystem

belowground.(426) It must be remembered that this may not represent the long-term

change of the system, however.(246,413) There is also a feedback between plants and

climate. For example, decreasing albedo because leaves are thicker increases the net

radiation.(245) Advance and recession of treelines alters albedo.(245)

Fig. E17.4.4 Earth’s regions in terms of suitability for rain-fed agriculture. Green and yellow regions aremore and less suitable, respectively, for agriculture. Note how favored east Asia, Europe, and NorthAmerica are compared to the other regions.(Reference 427, Fig. 4)

Fischer et al. consider the constraints that would be faced in increasing agricultural

production.(427) Fig. E17.4.4 shows the regions of Earth suitable (green and yellow),

unsuitable, or severely constrained in using rain-fed agriculture. In Fig. E17.4.4, the red

and orange regions suffer severe constraints at least some of the time. The gray regions are

unsuitable for agriculture altogether. As may be seen, the gray, red, and orange regions

overwhelm the eye. Good to fair agricultural regions are severely limited in Africa, South

America, and Oceania. In the mid-1990s, total cultivated land (rain-fed and irrigated)

totaled about 1.5 Gha. Overall, only about one-quarter of Earth, with an area of about 3.3

Gha (about double the present) out of the total of 13.4 Gha, is suitable for food

production on a sustainable basis.(427) Using the other half for agriculture would involve

major ecosystem disruption—most forests would disappear, for example. We already

know that deforestation increases warming, so this “solution” could be part of the

problem.

Many less developed countries are subject to severe terrain or climate constraints. There

are few untapped regions remaining and population pressure will put additional

constraints on agriculture. As Fischer et al. write, “[o]ver 80% of potentially cultivable

land reserves are located in just two regions, South America and sub-Saharan Africa. In

contrast, most of the cultivable land in Asia is already in use, and the population increase

expected by 2050 will reduce per capita availability of cultivable land to below the critical

level of 0. 1 ha per person.”(427)

Fig. E17.4.5 Areas of Earth that would have greater of less agricultural productivity in a warmer world of2080.[Reference 427, Fig. 11 (originally generated by the Max Planck Institute of Meteorology, ECHAM4climate model)]

As seen in Fig. E17.4.5, most developed countries outside Europe will be winners under

global warming expected by 2050, but few of the less-developed countries will gain, and

many will lose—Brazil and India, with more than 1.5 billion people between them in

2050, will likely be big losers. With the projected population growth, we expect that food

demand will rise there, and most particularly in Africa, which has some of the highest

population growth rates in the world.(428)

According to the IPCC, “climate change would lower incomes of the vulnerable

populations and increase the absolute number of people at risk of hunger, though this is

uncertain and requires further research. It is established, though incompletely, that climate

change, mainly through increased extremes and temporal/spatial shifts, will worsen food

security in Africa.”(59.,211) Daily et al. suggest that a set of “foresight institutions” be set

up to help monitor the future food situation and intervene with advice.(428) The

International Institute for Applied Systems Analysis report says “[t]he projected climate

change will result in mixed and geographically varying impacts on crop production.

Developed countries substantially gain production potential, while many developing

countries lose. In some 40 poor developing countries with a combined current population

of 2 billion, including 450 million undernourished people, production losses due to climate

change may drastically increase the number of undernourished, severely hindering

progress against poverty and food insecurity.”(427) This is one of the many places where

the IPCC recommendations for easing technical knowledge transfer would be useful.(429)

Satellite analysis of vegetation growth increase correlated with increased concentration of

carbon dioxide with a two-year lag.(430) This suggests to Braswell et al. an indirect

response more than a direct response.(430) In the temperate and the boreal regions, the

response was positive for warming and negative for cooling. Tropical plants showed the

reverse response, so the temperature itself may cause the plant problems, or it may

induce water stress.(430) After a time, the correlations may reverse. The reason for this

change is not known at present.(430)

Fresh water in United Kingdom rivers are carrying more dissolved organic carbon. The

reason may be that the extensive British peat soils are releasing carbon.(431) There may be

much more carbon in the ocean in a warmer world. This would probably inhibit transfer

of carbon from the air and cause a positive feedback, increasing warming. Already a study

has pointed to a decrease in oceanic net primary productivity since the 1980s.(432)

Furthermore, as we have mentioned, warm periods have often resulted in dust bowl

conditions in central continents.(1,25,63,65,69,352,363,369,433,434) Soil moisture in the Great

Plains, western Europe, northern Canada, and Siberia would decrease.(435) In the 1930s,

the dust bowl brought in its wake pests such as the jack rabbit and grasshoppers, whose

populations exploded.(361) Such “shifty pests” may throw all projections of crop

production awry.(36,80,422)

The IPCC has said that “[m]ost studies indicate that global mean annual temperature

increases of a few °C or greater would prompt food prices to increase due to a slowing in

the expansion of global food supply relative to growth in global food demand.” They call

this conclusion “established, but incomplete.”(211) Staple crops such as wheat, rice, and

soybeans use the C3 pathway, and may suffer a yield drop due to increased

temperature.(80) (Maize, sorghum, millet, and sugar cane use the C4 pathway.)

Effects that are felt by plants can be transferred throughout the ecosystem. During the

dry season in Costa Rica, clouds hover over rainforested regions. However, deforested

areas are relatively cloud-free.(436) This means that lowland land use affects the

rainforests. The authors of Reference 436 performed simulations, which suggest that

conversion of forest to pasture have a “significant impact” on the formation of clouds. A

similar effect was noted in the Appalachians. The cloud ceiling has risen 180 meters over

a three-decade period.(437) Since the ceiling marks the dividing line between deciduous and

evergreen trees in Appalachian forests,(438) this means the ecosystem has been moving

upwards on average roughly 6 meters (3 stories in a building) every year.

Humans and the urbanized world

Karoly et al.(439) assert that significant human influence has been exerted during the

twentieth century on the North American climate on the basis of manifold evidence. They

say “this influence is manifest not only in mean temperature changes but also in changes

of the north-south temperature gradient, the temperature contrast between land and

ocean, and reduction of the diurnal temperature range.”(439)

It is well known that cities form heat islands that affect local weather. Do warmer cities

contribute to warming of North America? It seems that, yes, they do add to the global

warming being experienced by North America. A study by Kalnay and Cai compared the

heat signature of North America with reconstructions of continental temperature profiles

(NCEP-NCAR 50-year Reanalysis) that does not reflect the effect of cities.(440) They

find a mean surface warming of 0.27 °C per century, about half the global warming effect.

Kalnay and Cai also identify half of the day-night temperature difference decrease as

being due to “urban and other land-use changes.”(440)

IPCC has recommended that regional projections be done by more local research groups.

That smaller scale resolution is more likely than large-scale projections to meet local needs

because the climate models’ grid size is so large. This was put into practice by a group

centered at the University of Illinois, which considered California’s future under two

possible scenarios—business-as-usual, and one with aggressive measures to reduce the

effects of global warming.(441) California has a challenging mix of biomes and has been a

leader in addressing pollution because of its infamous smog problem. As a result of

Californian environmental awareness, team leader Katharine Hayhoe was quoted as saying

“It might actually use our findings.”(442)

The group used two GCM models, the Parallel Climate Model and Hadley Centre

Climate Model, version 3, to simulate California’s future. Three of the four simulations

showed greater gains in summer than winter temperatures. In the lowest emission

scenario, Los Angeles will have four times as many heat waves as at present and many

more predicted heat-related deaths; in the highest emission scenario deaths are doubled

compared to the lowest scenario, while the temperature increase is also near doubled in

going from lowest to highest scenario. These effects occur because the elderly have

temperature regulation problems; a study showed that for each rise in mean external

temperature there was a corresponding rise about 15% as large inside the affected

person’s body.(443) At high enough ambient temperatures, these elevated internal

temperatures can cause brain damage and death.

Of course, heat waves are not just predicted for California in this century, but across

North America and Europe—and they will be more intense and of longer duration than at

present.(444) Heat waves in the northeast and midwest would have similar effects on

people living there as those in California (or Europe).(445)

The California snowpack is particularly vulnerable and is greatly reduced (by 30% to

70%) even in the milder scenario. Alpine and subalpine forests are greatly affected as

well; in the highest scenario, 75% to 90% of these forests disappear, and even in the

lowest at least half the forests disappear! Dairy production is reduced.(441,442)

Historically, incidence of fires in California have been corrlated to climate regimes.(446)

The report led to a publication by the Union of Concerned Scientists (UCS) aimed at

persuading Californians that reducing emissions is important.(447) The report and the

UCS also discussed the effect on winemaking of these possible futures. As wine is a $3

billion industry in California, this was the most important focus of the news reports.(448)

Surprisingly, global warming might be good to wine.(448,449) It was found that the wine

ratings (out of 100) rose about 13 for each degree Celsius rise in temperature.(449)

However, it might also be very bad for wine, especially in the already-warm big wine-

producing regions—as one observer prognosticated, “the vineyards will move from

producing gourmet wine to plonk.”(441) One example of reduced emissions is in the

California dairy industry. Research has shown that feeding animals that ruminate fish oils

can reduce substantially the amount of methane released by the animals.(450)

The extreme European heat wave of the summer of 2003 may be a harbinger of things to

come. Reports at the time convey a sense of desperation.(451) A report used Swiss

weather records from the period 1864 to 2000, and compared the temperatures of the

base period with those of the hot summer. There was no comparison. The temperature

anomaly of about 3 °C above the 1961-1990 mean in the Basel-Binningen, Geneva, Bern-

Liebefeld, and Zürich study area was 5.1 °C, or almost six standard deviations, above the

mean of the entire one and one-third centuries of data.(452) The closest anomaly to 2003

over the entire period was 2.7 °C above the mean, recorded in 1947. Schär et al. estimate

the “return period,” the frequency of an event or exceeding a limit; they find several

million years (not a sensible answer) using the 136 year record, and 46,000 years using

the period from 1990 to 2002, again nonsense. However, as they say, the parameter is

“merely used to express the rareness of such an extreme summer with respect to the long-

term instrumental series available.”(452) A simulation suggests an increase of 4 °C in

European mean summertime temperatures by the late twenty-first century.(453)

Since the summer temperatures are so far outside the variability of the instrumental

record, they hypothesize that the distribution of temperatures has changed, which signals

more such summers, many more. Schär et al. write “an event like summer 2003 does not

fit into the gaussian statistics spanned by the observations of the reference period, but

might rather be associated with a transient change of the statistical distribution.”(452)

Increasing the standard deviation of their distribution raises the probability of 2003-like

events by several orders of magnitude. That in turn would mean greater variability in

weather, more droughts, more heat waves.

Another model analysis from before the floods of 2002 found that the frequency of floods

would probably increase, as would weather variability.(454) The summer of 2002

produced sustained flooding across Europe. In Dresden, the Alte Meister museum was

able to save all the paintings only after the most strenuous efforts to move them higher

out of the way of the Elbe flood. The Christensens determine “that CO2-induced warming

can lead to a shift towards heavier intensive summertime precipitation over large parts of

Europe.”(454)

Thus two results—measurement and modeling—have come into confluence. The summer

of 2003 was extraordinarily hot. The summer of 2002 was exceptionally wet.

The European winter tourist industry is extremely concerned about the future. Ski resorts

are being moved up mountains and onto mountain glaciers.(455,456) Resorts nearer sea

level, such as the famous Kitzbuhl, face economic catastrophe.(456) All of Scotland’s ski

resorts were put up for sale by the desperate owners.(457) Guardian reporter Seenan

quotes a ski operator as saying “Unfortunately, it’s just getting too hot for the Scottish

ski industry ... It is very vulnerable to climate change; the resorts have always been

marginal in terms of snow and, as the rate of climate change increases, it is hard to see a

long-term future.”(457)

An additional worry is that heat waves, which can kill otherwise healthy elderly people

and small children, can lead to increased pollution. As was mentioned in Chapter 14, at

normal temperatures trees emit tiny amounts of hydrocarbons such as isoprene or terpene

naturally (think of the natural “smoke” of the Smoky Mountains). However, under heat

stress (say, by reaching ambient temperatures of 35 °C) the hydrocarbon emissions

skyrocket, so the heat makes trees emit more isoprene, the isoprene interacts with nitric

oxides emitted by tailpipes and makes a good deal of ozone, which causes additional

health problems all by itself.(458)

Such a course may lead to formation of the classic Los Angeles-type smog, making health

problems even worse. Up to the near present, Europe has not had many such smog

episodes. There are indications that that has changed.(459)

These foregoing circumstances must lead thoughtful people to quite sobering thoughts

about the future European climate. It behooves us to take preventative action, to build

early warning systems, to restrict development on flood plains, and so on.(460)

Floods

The 2002 floods in Germany and the Czech Republic cost $12 billion.(461) A British

government study suggests that future floods will cost up to twenty times as much to

deal with present flooding.(462) Two billion people could be at risk of floods.(463) If sea

level rises substantially because of melting of the Greenland ice sheet, the risk of flooding

increases tremendously, especially near the seashore.(464)

The large amount on money involved invites us to think about spending large (but

relatively small) amounts for research, mitigation, and prevention. Becker and Grünewald

list three ways to help control floods: “(i) reservoir systems for flood retention and

control in the mountainous headwater areas, ...; (ii) controllable polders (inundation areas

in valley floors and large lowlands), ...; [and] (iii) constructions to increase the carrying

capacity for flood flow, including canals parallel to the main stream.”(461) Clearly these

measures will cost money to implement, but also will clearly not cost as much as the

flood itself.

Technology promises some cost-effective approaches to flood. Examples include remote

sensing, computer monitoring of floods, early warning systems, reestablishment of

connections to wetlands, and flood reduction systems.(465)

Effects on animals

A. Fish and marine creatures and the fertilizer effect

A concern in the altered climate is that the warmer oceans will be more hospitable to

disease microorganisms.(386) Already the frequency of marine mammal mortality is on the

rise.(386) The Caribbean basin is a “hot spot” of disease; several species have been lost

there. Over a dozen coral diseases are attacking Caribbean coral reefs, only three of them

known to science before this.(386) This suggests that these are new diseases. Marine

diseases are being transmitted across species barriers, as in the case of the death of monk

seals off Mauritania from a dolphin megalovirus that had affected local dolphins.(386)

Toxic blooms have increased worldwide in the past three decades.(386) A dieoff in

European harbor seals was preceded by heightened temperatures.(386) An oyster disease

spreads in the Gulf of Mexico in response to ENSO events.(386) In addition to the effects

of warming, human activity has led to the spread of exotic organisms (usually through

ship bilges), to increased pollution, to decrease in coastal wetlands, and to spread of

disease through disposal of untreated sewage in the open ocean.(386)

Some changes in salmon streams over the past three centuries are due to local effects of

people, and some due to climate changes.(466) The starfish predator Pisaster ochraceus

eats its prey heartily at normal water temperatures, but when there is cooler upwelling

water (by only 3 °C), the predator loses its appetite.(467)

People are using fertilizer that runs off into streams and lakes and gives rise to nitrous

oxide (N2O). Agriculture is responsible for a majority of the worldwide N2O

emission.(145) Some of the nitrogen is stored by riparian ecosystems, and much of it

reaches the oceans, where it can be a problem. Streams in grassland areas absorb much

more nitrogen than those in forested areas,(468) because nitrogen disrupts forests’

ecosystems, effectively poisoning the forest at high enough concentration.(469) This

nitrogen is more likely to end up in the atmosphere as the greenhouse trace gas nitrous

oxide.(468,470) Lakes may be a source of carbon to the atmosphere of the reverse as a

result The effect depended on whether top predators were active in the lakes. If the

grazers were unable to suppress NPP, the lake became a source of carbon. The top

predators therefore control the internal ecosystem dynamics.(471)

B. Insects

Because insects are all around us and widely ignored, warming could be affecting them

without our recognizing it. Butterflies have human enthusiasts, and a British naturalist

enlisted British lepidopterists to learn about what was happening to British butterflies. A

butterfly census was taken in over 2,800 pre-established 10 km by 10 km areas. The data

consisted of time-separated census numbers. Butterflies were being lost 10 to 100 times

faster than plant species in the census tracts.(472) According to Thomas et al., the

widespread decline in butterfly populations relative to other species has major

implications. They note with alarm that

the only insect taxon to have been rigorously compared with plants or birds

at this temporal or spatial scale experienced at least as many regional

extinctions when exposed to the same range of environmental changes that

afflict plants and vertebrates worldwide. If insects elsewhere are similarly

sensitive, we tentatively agree with the suggestion that the known global

extinction rates of vertebrate and plant species may have an unrecorded

parallel among the insects, strengthening the hypothesis, derived from plant,

vertebrate, and certain mollusk declines, that the biological world is

approaching the sixth major extinction event in its history.

The genetic pattern of the pitcher-plant mosquito (Wyeomyia smithii) has shifted toward

shorter day length as the climate has warmed. Most changes are non-genetic, and this was

the first evidence of evolutionary genetic change occurring in response to climate

change.(473) The change affected all samples collected (from Florida to Canada). According

to the authors, “W. smithii represents an example of actual genetic differentiation of a

seasonality trait that is consistent with an adaptive evolutionary response to recent global

warming.”

Butterflies are appearing earlier than in earlier times.(414) Spanish butterflies shifted

almost two weeks forward between 1975 and 1994; British butterflies appear earlier

also.(414)

Many butterflies that were expected to prosper in warming climates are in decline in

Britain. Only mobile, generalist species succeeded, however. Other generalists and

habitat-bound species declined.(474) Habitat degradation and climate warming caused the

decline of specialist butterflies.(474)

Warming is disrupting the feeding of the winter moth (Operophtera brumata). If the moth

hatches too early, there is no oak leaf food, while if it hatches too late, the leaves’

integument is too tough. The problem comes because the timing of the oaks and the moth

operate differently.(475) Warmer springs get the moths to hatch earlier. Some moth

caterpillars are emerging three weeks too early, and no oak leaves are available.(475) The

oaks operate on the basis of cold days, which hasn’t changed with temperature.(475)

Tiger mosquitoes (Aedes albopictus) raised in the laboratory were found to breed faster at

higher temperatures. This means that they may increase rapidly in the wild in response to

rising temperatures.(476) These mosquitoes can carry around 100 diseases and they seek

out humans and feed voraciously, increasing the probability of disease transfer. The tiger

mosquito came from Asia into the United States only in 1985, but it has spread widely

and its range is temperature-dependent. Rising temperatures translate into an extended

range.

C. Birds

Many migratory bird species are undergoing precipitous declines.(477) Research has

shown that this might be partly climate-related. The breeding success of the black-

throated blue warbler cycled in the north so it was lower under El Niño conditions and

higher under La Niña conditions.(478) In addition, the conditions in the winter grounds can

also affect survival.(477) Survival was low in the wintering grounds in Jamaica in El Niño

years and high in La Niña years.(478) This demonstrates that the birds get hit twice

unfavorably by the same climatic conditions.

The history of Atlantic albatrosses gives pause. There are no Atlantic albatrosses at

present, but there were 400,000 years ago. They became extinct after a sea-level rise of

some 20 m and storm surges drowned them in their island breeding grounds.(479) While

the higher-lying parts of the island were still welcoming to the birds, they never were able

to recolonize and became extinct. Could similar extinctions occur during the global

warming era?

Tufted puffins (Fratercula cirrhata) reproductive success is extremely closely tied to

local temperatures and weather.(480) For the puffins, higher temperatures lowered the

number of fledglings that became adult. Global warming will have a strong effect on

puffins; changing habitat may send them elsewhere than ancestral breeding grounds (and

we have little knowledge of how successful such a transition would be). Likewise, black-

throated blue warblers (Dendroica caerulescens) reproductive success is strongly

influenced by ENSO, and global warming is predicted to increase the severity and

frequency of El Niños.(481)

Many states have state birds. Warming at the end of the twenty-first century will have

moved the ranges of, for example, the Baltimore oriole (Maryland) and the black-capped

chickadee (Massachusetts) enough that they will not be found in their present “home

state.”(482) Price and Glick, in The Birdwatcher’s Guide to Global Warming point out

possible warming impacts:(482)

In addition to altering species’ ranges, global warming could have a direct

effect on birds’ habitat and behavior. As temperatures rise and precipitation

levels change, the abundance of the birds’ key food sources may shift. In

some cases, the amount of available seeds, insects, or other foods may expand

or decline in wintering habitat, affecting birds’ health for migration and

breeding. Similarly, plants may bloom or insects may hatch too early (or too

late) for birds’ spring arrival in their summer habitat, which could affect their

reproduction success or disrupt important pollination.

Arrival times of migratory birds in Oxford, U. K.has advanced by 8 days over the course

of the last 30 years.(483) This suggests “a highly probable link between global climate

change and the migratory phenology of many bird species.”(483) A study of bird arrival at

Helgoland in the Baltic, a stopping point for migratory birds on their way to Scandinavia,

separated birds into short distance migrants and long distance migrants. Twenty-four

species had sufficient records to be assessed, a dozen in each class.(484) The study found

that twenty-three out of the twenty-four bird species arrived earlier, but each class for a

different reason. The short-distance migrants’ arrival times depend on local temperature;

the long-distance migrants’ arrival times correlate with the NAO index, which depends on

air pressure over the North Atlantic. The higher the index, the earlier the arrival.(484)

The dipper (Cinclus cinclus) inhabits the subarctic region. The numbers of birds in

southern Norway increased in numbers in response to a change in the North Atlantic

Oscillation (NAO) index. When the NAO index is high, climate in Europe is milder than

when it is low. About half the variance in reproductive success of the dipper is explained

by mean winter temperature. Population is expected to increase under global warming

conditions: The long-term warming experienced by the birds was 2.5 °C, which led

through a nonlinear relationship to an increase of 58% in the system carrying

capacity.(485)

Across North America, tree swallows’ mean clutch initiation date advanced 9 days over

the period from 1959 through 1991, based on evidence from 2,881 clutches. Variance of

swallows’ lay date was smallest in the warmest years.(486)

In a warmer world, the frequency of droughts in the midwest is expected to increase; most

models show this. GCMs predict such droughts could cut breeding populations of ducks

at the ponds in half.(487)

A change in the timing of insect maturation, according to Price and Glick,(482) should have

to shift the timing of the birds that feed on the insects—but does it? French blue tits

(Parus caeruleus) appear to have large variations in breeding dates among different

populations, which seem to be “hard-wired.”(488) Blue tits feed on caterpillars that

emerge with a timing set by the climate. Data were gathered on the energy expenditure of

the birds. It was found that one breeding population that was usually found in a

deciduous oak forest sometimes are found also in an adjacent “overflow” region inhabited

by evergreen oak, where their timing was off by over three weeks. These birds were

running at a much higher metabolic rate, one hard to sustain. They had to do this because

the caterpillars at their oak site in France emerged earlier than the birds anticipate on the

basis of the deciduous oak. The birds in their home deciduous forest did not have to work

so hard. A control group living in an evergreen oak forest in Corsica, which was

synchronized to the arrival of caterpillars, did not have to work so hard to feed and did

not have enhanced metabolic rates.(488)

The laying dates of Dutch great tits do not match their prey group appearance due to

warmer springs, while British great tits had changed their timing.(489) This raises the

danger that mistiming will become common (see the discussion about the mistimed moths

above).

Mexican jays have responded to the increase in nighttime temperatures and the decrease

in the diurnal temperature difference by setting eggs earlier each season—J. Brown found

that the eggs in 1998 were laid 10 days earlier than in 1971, during which time the daily

minimum temperature had gone up 2.7 °C.(490) The reason may be that insects are

emerging earlier, or some other reason, but the change in climate is changing the bird’s

behavior.

D. Mammals

The Virginia opossum is already moving into New England. The orange-spotted sunfish is

moving north from Ohio to Michigan. Northern fish once common in Michigan have gone

farther north.(491) In northern Ontario, air and lake temperatures have increased by 2 °C

and the length of the ice-free season increased by 3 weeks over the past 20 years.(491)

Lake trout and opossum shrimp decreased.(492)

Such habitat shifts will affect the species found in American National Parks. The outlook

is not good for species conservation: “Due to species losses of up to 20% and drastic

influxes of new species, national parks are not likely to meet their mandate of protecting

current biodiversity within park boundaries.”(493) On a worldwide basis, conservation

will depend on enlistment of indiginous people by, for example, revenue-sharing from

tourism dependent on habitat conservation.(494) It will require the world to move from lip

service to conservation to actual commitment, a difficult transition indeed based on the

evidence up to now.

Sex ratios of alligators and turtles might become skewed, because they depend on the

ambient temperature.(495) With a 3 °C warmer world, native fish will not be able to live in

Lake Erie.(496)

The NAO that affected the dippers also appear to affect northern ungulates (seven

species of hoofed grazing animals were studied). Plants bloomed earlier and longer under

high NAO index, and more snow lay on the ground in milder winters and fewer animals

survived. The NAO index was correlated with over half the body weight.(497) Wild red

deer (Cervus elaphus) and domestic sheep (Ovis aries) sampled on the west Norwegian

coast show similar patterns of growth behavior dependent on the NAO index, despite

their greatly differing habitat.(498) It seems that because of predator-prey relationships

and dependence of herbivores on plant success, population dynamics of different species

are synchronized. This occurs even over long distances, for example, in synchrony

between populations of musk oxen and caribou.(499) Similar climate-induced synchrony

was observed for Canadian lynx (Lynx canadensis) and the snowshoe hare (Lepus

americanus).(500)

Climate change has caused the timing of breeding to change for American red squirrels

(Tamiasciurus hudsonicus) in the Yukon. The squirrels are now breeding 18 days earlier

than they were the previous decade. The Yukon has been warming in spring and this

means more food earlier for the squirrel.(501)

Population extinctions of 20 of the 50 frog and toad species in a plot of Costa Rican

rainforest were correlated with dry (mist-free) days. Rising sea surface temperatures

increase the frequency of dry days.(502)

The American pika (Ochotona princeps) may be experiencing an extinction episode due to

global warming. A National Park Service survey found that 7 out of 25 historical

populations of pika had disappeared from the Great Basin.(503) The population loss

happened due to warmer temperatures, “contributing to apparent losses that have

occurred at a pace significantly more rapid than that suggested by paleontological

records.”(503) As Beever et al. note, this is one of just a “few documented instances in

which a medium- to small-sized mammal in North America has apparently experienced

extirpations at a bioregional scale over the span of only a few decades (55–86 years since

last record).”(503)

Climate change could be causing problems for penguins (Eudyptes chrysolophus), seals

(Arctocephalus gazella), albatross (Thalassarche melanophrys), and gentoo penguins

(Pygoscelis papua) living on South Georgia Island (near the Antarctic). The krill

(Euphausia superba), their food supply, apparently are not breeding as well as in the

past. Fewer animals were breeding and the breeding success matched the numbers of krill

available.(504)

As we discussed in Extension 17.3, General Circulation Models’ problems, cross-scale

interactions are very important to consider in studying climates’ effect of species. There

can be surprising interactions among species at different levels of the trophic

pyramid.(505) Climate change always happens, but the scale of modern climate change

may be unprecedented. A study around Lago Consuelo in the Andes over 48,000 years

shows that the ecosystem does respond seamlessly to climate changes that are caused by

temperature changes of 1 °C per millennium.(506) Humans are changing the temperature at

about 1 °C per century! On mountainsides, there is not much vertical distance between

climate regimes, while on flatter topography, the distances may be far too long to manage

quickly, especially for plants.(506)

There was a study of the possible effects of climate change in Mexico involving 1870

species and two future climate scenarios. It found few episodes of extinction or greatly

changed species range. However, it did find that 40% of species could turn over in any

given biome, indicating that “severe ecological perturbations” could occur.(507)

One concern is that climate and human intrusion together form a powerful engine for

extinction of species. Fossils of over 20,000 animals from between 600,000 and a million

years ago found in Porcupine Cave, Colorado, were studied for evidence of climatic

effects. The evidence shows that climate mainly affects smaller animals at lower trophic

levels.(508) Human beings predominantly affect larger animals and predators (higher on the

trophic pyramid).

E. Marine animals

An investigation of outflow water from a hot water outflow to dissipate water heat from

a power plant raised the temperature of Diablo Cove, California. The Cove was studied

for over 18 years.(509) A 3.5 °C rise in temperature affected about 2 km of coast in the

vicinity of the outflow. (Such temperature rises can occur naturally for short periods of

time during ENSOs.) Significant changes in 150 species of invertebrates and algae were

found relative to an untreated adjacent control area. There was no replacement of species

by species from warmer waters, as had been expected. The most temperature-sensitive

plants decreased the most in numbers.(509) Despite the fact that the sustained heightened

temperature is greater than that sustained by California in the twentieth century, it

provides a window on the possible warm California coastal future of the twenty-first

century.

Recent warming led to an invasion of jellyfish and sea squirts in Long Island Sound. In

Narragansett Bay, flounder numbers have plummeted and sea squirts and combjellies

increased.(510) Alien invasions such as these will become more common in the warmer

world.(511) Such changes seem to be multiplying worldwide.

Global warming has already had an effect on the oceanic food web. Plankton in the North

Atlantic shifted in response to the changes as was seen in a study of the oceanic

ecosystem from 1958 to 2002.(512) Phytoplankton increase in regions originally cooler as

they warm; however, they decrease in regions that get too warm. The changes in plankton

propagate through the trophic pyramid in a bottom-up fashion to copepods (grazers) and

then to plankton carnivores and finally to fish and the fish, birds, and pelagic mammals

that prey on them. Since 1987, the phytoplankton blooms have gradually gotten out of

synchronization with the zooplankton grazers because the warming moves different

plankton forward in time at different rates.(513)

These results are in basic agreement with the findings of a group that used six different

GCMs and developed an empirical way to relate the model outcomes to chlorophyll

production. They find that the polar margins’ productivity plummeted in both Northern

and Southern Hemispheres, down by 42% and 16%, respectively. Productivity in the

midlatitudes, now low, increased—but by under 10%.(514)

These results indicate that climate change will have a big effect on the oceanic food web

by determining if and where within a region fish will congregate.(512,513) Such an effect

has been seen in Atlantic cod (Gadus morhua L.), which have been severely overfished

for about the last 40 years. Larval cod are now finding it problematic to get food.

Beaugrand et al. find that “rising temperature since the mid-1980s has modified the

plankton ecosystem in a way that reduces the survival of young cod.”(515)

Lobsters in the Atlantic had recently been suffering a mysterious decline. The problem

has been creeping northward toward Maine up the northeast coast for some years.

Simultaneously, lobsters to the south appeared to be suffering from excretory calcinosis, a

condition in which a gritty substance, later identified as calcium, gets into the gills. The

lobster’s metabolism was bollixed up. A Stony Brook scientist, Alistair Dove, believes

that global warming is responsible for the stress.(516)

Coral reefs have been experiencing difficulties around the world’s tropics. For example, a

core taken in Discovery Bay, Jamaica shows a record of healthy reef life over 1260 years

until the 1970s and 1980s, when it died out.(517) A similar catastrophic collapse after

3000 years was also seen in the Belizean shelf lagoon.(518) Worldwide, corals have been

declining over thousands of years, long before the current dieoffs and episodes of

bleaching began.(519) The higher temperatures are known to affect the corals’ algal

symbionts as well, with one variant of Symbiodinium that is heat-resistant being much

more abundant after episodes of coral bleaching or dieoff than others.(520) Caribbean coral

reefs have been hit hard, with coverage reduced to 10% to 50% from a mean of 80% since

the 1970s.(521) However, Acropora corals are at the same time expanding their range

northward from the Caribbean to cooler waters.(522)

Given the widespread and consistent degradation of reef communities, strong action

seems necessary. Localized protection status, or even bigger protected areas such is found

around the Great Barrier Reef, will not be enough.(519,523) Pandol makes a clear, strong

statement:(519) “Regardless of the severity of increasing threats from pollution, disease,

and coral bleaching, our results demonstrate that coral reef ecosystems will not survive for

more than a few decades unless they are promptly and massively protected from human

exploitation.” Rather than focusing on protecting high-diversity hotspots, Bellwood et al.

argue that areas of low species richness are more needful of protection, as they recognize

that “Caribbean Basin, the Eastern Pacific, and many high-latitude or remote locations in

the Indo-Pacific have low functional redundancy, where functional groups may be

represented by a single species.” When this is the case, “minor changes in biodiversity can

have a major impact on ecosystem processes and consequently on the people whose

liveli-hoods depend on the services that ecosystems generate.”(523)

Lacustrine effects

The most closely studied lake is Lake Tanganyika, since the British colonial government

made numerous measurements from the late 1800s. A deep tropical lake like Lake

Tanganyika is ideal for testing global warming effects because mixing is relatively low and

inflow and outflow minor relative to the total volume.

The lake provides a century of global warming data. These data show that the lake has

become more transparent, that mixing has slowed, and that productivity has decreased.

The mass of plankton is one-third of its value from less than three decades ago.(524)

Primary productivity of the lake is down 20% as inferred from isotope measurements and

the number of fish is down 30%.(525) The catch of sardines, in agreement with what was

inferred from these measurements, is down by 30% to 50% since the 1970s.(525)

Warming and agriculture

A simulation of warmer climate with GCMs examined possible future agriculture in the

2030s and the 2090s. Most aspects of farm economy were studied with and without

ENSOs. In addition, the Chesapeake Bay region was studied extensively, as was the

Edward’s Aquifer in San Antonio, Texas. Both these systems exhibited increased levels of

nitrogen.(526)

The temperatures produced by the Canadian Climate Center model they used are much

higher than for other climate models. The Hadley Center model used gives less extreme

temperatures, but predicts quite high rainfall for the U.S. In contrast to other studies,

they find greater yields in 2090 than in 2030, that is, U.S. agriculture is predicted to

become more productive.(526) This is presumably because of the increased precipitation

experienced.

This prediction supports a surprising result: U.S. agricultural production from the 1940s

on benefited from climate change, at least for corn and soybeans. The study identified

about 20% of the yield gains as due to climate change.(527)

Jones and Thornton find that maize crops in Africa and Latin America are harmed by

warming. Their model, which uses an 18 km by 18 km grid, predicts a 10% decrease in

maize harvest in 2055 and consequent loss of about $2 billion/yr.(528) The effect is

regional as well, with some regions gaining and some losing—it’s just that more lose than

gain in the continentwide analysis.

Risks to the ecosystem and its parts

Species extinctions are occurring now.(401) Global patterns of endemic species are thought

to arise from climatic variation. Jannson finds a “negative relationship between endemism

and temperature change [that] was robust to variation in area, and remained across more

than two orders of magnitude of variation in area. ... Endemic-rich areas are predicted to

warm less in response to greenhouse-gas emissions over the next 100 years than endemic-

poor ones.”(529)

Fires are more likely, and large ones even more likely in a warmer world. A study of the

history of fires in Yellowstone National Park over the preceding 17,000 years from a lake

core showed that the frequency of fires increased significantly when the climate was

warmer.(530)

Insects are more diverse and put more pressure on plants they get nearer to as the

Equator and the temperature goes up. This suggests that in a warmer world, insect grazers

will increase their predations with increasing temperature. In the fossil record of past

warmings, evidence has been found for exactly this effect.(531)

According to the IPCC, “some species currently classified as ‘critically endangered’”

would “become extinct and the majority of those labeled ‘endangered or vulnerable’”

would “become rarer, and thereby closer to extinction.” The IPCC places high confidence

in this outcome.

The IPCC also suggests adaptation methods that could reduce extinction risks to species.

They are:

“1) establishment of refuges, parks, and reserves with corridors to allow migration of

species, and

2) use of captive breeding and translocation.”

However, they point out that these options could be quite costly.(210)

What are “dangerous levels” of CO2?

To my knowledge, the question was forst posed by Stephen Schneider.(a) Schneider was

responding to the release of the IPCC’s third assessment report. One outcome (see details

in Extension 17.1, The IPCC) was that the report raised the previous prediction of the

temperature anomaly (rise due to human intervention) from 1–3.5 °C to 1.4–5.8 °C. For

Schneider, this raised the question of the likelihood that a temperature rise of 6 °C would

occur, and whether that level of temperature rise has “dangerous” consequences.(a)

Hansen writes of four points that he believes shows that Earth is already experiencing

“dangerous levels” of carbon dioxide.(b) They are:

(1) with the ~ 0.5 °C warming of the past 50 years, global temperature now

(Figure 1) approximately matches the peak level of the current (Holocene)

inter-glacial period, which occurred about 6000–9000 years ago,

(2) the global mean temperature during the penultimate (Eemian) and the

several previous interglacial periods was not more than about 1 °C greater

than the peak Holocene temperature,

(3) the Earth is now out of energy balance with space by at least 0.5–1 W/m2,

implying that an additional global warming of close to 0.5 °C is already “in

the pipeline”, and

(4) the greater warmth in some previous interglacial periods led to sea level

being several meters higher than today.

As indicated by Hansen and coworkers, and by Wigley (see the section “Future climates

and their effects” in Extension 17.3, General Circulation Models’ problems) the

warming commitment needs to be taken seriously.

Wigley remarks that “dangerous levels” will have been exceeded when the global

temperature anomaly exceeds 5.7 °C.(c) Because of the warming commitment, this means

that this point will be passed when Earth’s temperature anomaly is around a degree below

that value. This is a problem in human ability to assess risk, which is sometimes not as

sharp as one would wish. Wigley writes:(c)

Choosing a stabilization target for CO2 is essentially a risk assessment

problem, where the choice depends on what is deemed to be an acceptable risk.

For example, if we were to choose the median target in the base case, 536 ppm

(and ignore the effects of non-CO2 mitigation and adaptation), are we willing

to accept a 50% probability that such a target may lead to unacceptable

damages?

Dessai et al.(d) point out the important difference between what they call “external” and

“internal” definitions for risk.

External definitions are usually based on scientific risk analysis, performed by

experts, of system characteristics of the physical or social world. Internal

definitions of danger recognise that to be real, danger has to be either

experienced or perceived – it is the individual or collective experience or

perception of insecurity or lack of safety that constitutes the danger. A

robust policy response must appreciate both external and internal definitions

of danger.

Dessai etal. argue that much more attention needs to be placed on the “internal”

definition, partly because of the virtually exclusive use of the “external” definition.(d) This

seems a likely way to bring reluctant legislators and citizens to a proper appreciation of

the risks of doing nothing and the costs of doing something about global warming given

the climate change it will inevitably bring.

How much can the temperature change before it causes a disasterous change? This is an

active research question, but not usually asked as such. There is a risk in being too willing

to declare that a disaster is in the making; it is equally risky to decline to raise the alarm

when needed. The citizens of the world need to appreciate the tradeoffs required because

they will have to pay the ultimate costs.

References in addition to those listed for this chapter are shown in red in the text, and

listed below:

a. S. H. Schneider, “What is ‘dangerous’ climate change?,” Nature 411, 17 (2001).

b. J. E. Hansen, “A slippery slope: How much global warming constitutes ‘dangerousanthropogenic interference’?,” Clim. Change 68, 269 (2005).

c. Tom M.L.Wigley, “Choosing a stabilization target for CO2,” Clim. Change 67, 1(2004).

d. S. Dessai, W. N. Adger, M. Hulme, J. Turnpenny, J. Köhler, and R. Warren, “Definingand experiencing dangerous climate change,” Clim. Change 64, 11 (2004).