Satellite Measurements of the Earth’s Radiation Budget

NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

Earth’s energy budget (averaged over the whole globe and over a long time

• At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave• At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

Atmospheric influences on radiation

Absorption Absorption (absorber (absorber warms)warms)

ReflectionReflection ScatteringScattering

Atmospheric Absorption - The Greenhouse EffectAtmospheric Absorption - The Greenhouse Effect

Transparent Transparent to solar to solar (shortwave) (shortwave) radiationradiation

Opaque to Opaque to earth’s earth’s (longwave) (longwave) radiationradiation

Major GH gases: CO2, H20(v), CH4

Global Energy Balance II:The Greenhouse Effect

The importance of methane (CH4)• 23 times more powerful as a greenhouse gas than CO2

• The livestock sector is a major player, which accounts for 35-40% global anthropogenic emissions of methane (their burps!)

• The livestock sector is responsible for 18% of total greenhouse gas emissions, which is higher than transportation (cars, airplanes, etc)

• Therefore, consuming less meat is more efficient in reducing global warming than not driving cars.

3 Types of Scattering: 1. Raleigh2. Mie3. Non-Selective

Atmospheric Scattering

A discussion of each type follows…A discussion of each type follows…

1) Rayleigh scattering• involves gases, smaller than insolation

wavelength• scatters light in all directions • most effective at short wavelengths

(violet, blue)…hence, blue sky• explains reddish-orange sunsets when

light travels through thick slice of atmosphere

2) Mie scattering– involves aerosols (e.g. dust, smoke) larger than

gas molecules– forward scatter– equally effective across visible spectrum– explains hazy, gray days

3) Non-selective scattering– water droplets in clouds (larger than gas

molecules)– Act like lenses; scatter all wavelengths equally

Net Radiation and Temperature

• Earth’s radiation balance is a function of an incoming and outgoing radiation equilibrium (SW + LW = Net)

• If parameters were changed, a new equilibrium would be achieved

• Balances occur on an annual global scale and diurnally over local spatial scales

Daily/Seasonal Radiation Patterns

• insolation peak vs. temperatureinsolation peak vs. temperature• daily lagdaily lag• seasonal lagseasonal lag•Lag is function of type of Lag is function of type of surface, wetness, wind, etcsurface, wetness, wind, etc

• Temperature increases whenTemperature increases when input > outputinput > output• Temperature decreases whenTemperature decreases when input < outputinput < output

• tropic-to-tropic – energy surplus• poles – energy deficits• ~ 38o N/S – balance

• imbalance of net radiation at surface Equator/Tropics vs. high latitudes

• drives global circulation• agents: wind, ocean currents, weather systems

Latitudinal Variations in Net Radiation

Seasonal variation of surface radiation

Seasonal variation of surface energy budget

Storage change = net radiation - latent heat flux - sensible heat flux

Principal Controls on Temperature

1. Latitude2. Altitude3. Atmospheric Circulation4. Land-Water Contrasts5. Ocean Currents6. Local Effects

Seasonal variation of surface air temperature

• T decreases poleward• larger T gradient in winter• isotherms shift seasonally• T over land > water in summer• NH steeper T gradient

Seasonal Seasonal Temp Temp

DistributionsDistributions

Temperature Ranges (Summer minus Winter)Large over land, small over ocean

Climate Change:Fitting the pieces together

Presented by:

Your Name Here

• The topic of climate change is like a puzzle with many different pieces—oceans, the atmosphere, ecosystems, polar ice, natural and human influences. Scientists have been working on this puzzle for more than a century, and while there are still gaps in our knowledge, most experts feel we have the puzzle is complete enough to show that human activities are having an adverse effect on our planet. This talks looks at many of those puzzle pieces, the evidence behind them, and the conclusions we can draw from them.

Outline

• What changes climate?• Is it real?• How do we know?• Why should we care?• How sure are scientists?• What next—what can we do?

• Scientists have a good understanding of what has changed earth’s climate in the past:• Incoming solar radiation is the main climate driver. Its energy output increased about 0.1%

from 1750 to 1950, increasing temperatures by 0.2°F (0.1°C) in the first part of the 20th century. But since 1979, when we began taking measurements from space, the data show no long-term change in total solar energy, even though Earth has been warming.

• Repetitive cycles in Earth’s orbit that occur over tens of thousands of years can influence the angle and timing of sunlight.

• In the distant past, drifting continents make a big difference in climate over millions of years by changing ice caps at the poles and by altering ocean currents, which transport heat and cold throughout the ocean depths.

• Huge volcanic eruptions can cool Earth by injecting ash and tiny particles into the stratosphere.

• Changes in the concentration of greenhouse gases, which occur both naturally and as a result of human activities, also influence Earth’s climate.

What changes climate?

• Changes in:– Sun’s output– Earth’s orbit– Drifting continents– Volcanic eruptions– Greenhouse gases

• Scientists have a good understanding of what has changed earth’s climate in the past:• Incoming solar radiation is the main climate driver. Its energy output increased about 0.1%

from 1750 to 1950, increasing temperatures by 0.2°F (0.1°C) in the first part of the 20th century. But since 1979, when we began taking measurements from space, the data show no long-term change in total solar energy, even though Earth has been warming.

• Repetitive cycles in Earth’s orbit that occur over tens of thousands of years can influence the angle and timing of sunlight.

• In the distant past, drifting continents make a big difference in climate over millions of years by changing ice caps at the poles and by altering ocean currents, which transport heat and cold throughout the ocean depths.

• Huge volcanic eruptions can cool Earth by injecting ash and tiny particles into the stratosphere.

• Changes in the concentration of greenhouse gases, which occur both naturally and as a result of human activities, also influence Earth’s climate.

“Greenhouse effect” Increasing greenhouse gases trap more heat

• [Image 1] Earth’s surface absorbs heat from the sun and then re-radiates it back into the atmosphere and to space.

• [click, Image 2] Much of this heat is absorbed by greenhouse gases, which then send the heat back to the surface, to other greenhouse gas molecules, or out to space. Though only 1% of atmospheric gases are greenhouse gases, they are extremely powerful heat trappers. By burning fossil fuels faster and faster, humans are effectively piling on more blankets, heating the planet so much and so quickly that it’s hard for Mother Nature and human societies to adapt.

Greenhouse gases

Nitrous oxide

Water

Carbon dioxideMethane

Sulfur hexafluoride

• While there are many substances that act as greenhouse gases, two of the most important are water and carbon dioxide, or CO2.

• [Image 1] CO2 comes from a variety of sources. For example, plants take up carbon dioxide in the air to make wood, stems, and leaves, and then release it back into the air when the leaves fall or the plants die. The concern today is that fossil fuel use is putting huge amounts of CO2 in the atmosphere at a rate faster than the climate system can adapt to.

• [click, Image 2] In addition, the warming resulting from CO2 and other greenhouse gases also has the effect of increasing evaporation. This adds water vapor to the atmosphere as well. Water vapor is the most important gas in the natural greenhouse effect, contributing 60% of the effect to carbon dioxide’s 26%. And in fact, satellites have detected an increase in atmospheric moisture over the oceans at a rate of 4% per degree F of warming (7% per degree C) since 1988. This additional water vapor amplifies the warming effect.

Could the warming be natural?

• Certainly, past temperatures past have been higher (and lower) than today, and• CO2 concentrations have also varied. Large global swings were probably caused by

such things as changes in Earth’s orbit, which changed the distribution of sunlight over the planet. When this caused warming, more CO2 and other greenhouse gases were released, producing additional warming.

• [click to reveal today’s CO2 level] But today, the CO2 released by human activities is far above amounts in the previous 800,000 years. This CO2 is triggering the increase in temperatures we’ve seen.

Is it real?

Effects: Snow and ice

Grinnell Glacier, Glacier National Park1900 and 2008

Effects: Snow and ice

Grinnell Glacier, Glacier National Park1900 and 2008

Effects on precipitation

• Earth is getting warmer by virtually every measure we know, and the temperature has been well above normal for more than 25 years. Although increases of 1.0-1.6°F (0.6-0.9°C) over the last century or so may not sound very threatening, remember that’s a global average. The warming is stronger over land than over oceans and in the higher latitudes than in the tropics.

Effects on ecosystems

How do we know?

Present day observations

Increased warmth has also affected living things. For example, the Japanese keep very detailed records on the blossoming of their Tokyo cherry trees, so

they know they are blooming 5 days earlier on average than they were 50 years ago.

Also mosquitoes, birds, and insects are moving north in the Northern

Hemisphere.

Computer models

Computer models

• [Image 1] The main tool for both past and present climate analyses are computer climate models. Much like the models used to forecast weather, climate models simulate the climate system with a 3-dimensional grid that extends through the land, ocean, and atmosphere. The grid may have 10 to 60 different levels in the atmosphere and surface grid spacings of about 60 by 90 miles (100 by 150 km)—the size of Connecticut. The models perform trillions of calculations that describe changes in many climate factors in the grid.

• [click, Image 2] The models project possible climates based on scenarios that cover a range of assumptions about global population, greenhouse gas emissions, technologies, fuel sources, etc. The model results provide a range of possible impacts based on these assumptions.

Aspen, CO Forecast:

Partly cloudy todayHigh : 28°FLow: 13°F

Increasing clouds over night. Colder tomorrow.

Aspen, CO Forecast:

Partly cloudy todayHigh : 28°FLow: 13°F

Increasing clouds over night. Colder tomorrow.

[Image 1] A common critique of climate predictions is, “If weather model forecasts aren’t reliable more than a week out, how can models predict climate decades in the future?” While weather and climate models are based on similar physics, they

are not predicting the same thing. Weather forecasts look at the day-to-day changes on a local level, and subtle chaotic

atmospheric variations make short-term weather forecasts difficult beyond 8-10 days.

[click, Image 2] Climate predictions are focused on longer-term influences of the sun, oceans, land, and ice on the atmosphere.

Instead of predicting a temperature at a particular place at a particular hour, climate modules project an average

temperature over a year or longer in a large region or over the entire globe.

Climate models are not only used to look at how climate might change, they’re also used to figure out WHY it’s changing. When models are run with only natural

influences from the sun and volcanic eruptions, they say that during the latter half of the 20th century, we would have expected little change from normal conditions (the blue line). Only the addition of human emissions (greenhouse gases, sulfates, and

ozone) produce the model results in red that most closely reproduce the black line of actual observations.

So, although they aren’t perfect, climate models can reproduce many of the larger features of climate change in Earth’s distant past, and they replicate the pattern of warming in the last 100+ years. This gives us confidence that they correctly identify that the warming is due to man’s activities, and that projections of future warming

are realistic.

Why should we care?

Global average temperatures are expected to increase by about 2-13°F (1-7°C) by the end of the century. That may not sound like a lot, so what’s the big deal? The problem is that small changes in global average temperature can lead to really large changes in

the environment. Let’s look at some of the expected changes.

2003 European Heat Wave

Germany: Lowest river levels this century

Switzerland: Melting glaciers, avalanches

France: >14,000 deaths

Portugal: Forest fires

U.K.: Train rails buckle

[Image 1] There will always be natural variability, and some places and some years will be warmer or cooler than average. In general, however, summers will get hotter, not only because of higher temperatures but also because humidities will increase. That means that heat waves, like the one that killed 35,000 people in Europe in 2003, will

become more common.

[click, Image 2] On the plus side, winters will be warmer in many places, reducing heating bills. And the number of days with frosts is likely to decrease.

Sea-level rise projections : a few inches to a few feet

•2 ft: U.S. would lose 10,000 square miles•3 ft: Would inundate Miami•Affects erosion, loss of wetlands, freshwater supplies•Half of the world’s population lives along coasts•Big question: Ice sheets

The oceans will continue their rise in the coming century. The IPCC’s best estimates range from a few inches to a few feet by 2100. If the rise is 2 feet, the US could lose 10,000 square miles, If they rise three, they will inundate Miami and most of coastal Florida. Sea-level rise also increases coastal erosion and the loss of coastal wetlands, and saltwater spoils freshwater drinking supplies. Coastal populations become even more vulnerable to storm surge and flooding. Considering that half of the world’s population lives near coasts, sea-level rise is a serious concern.

The big unknown in all this is how much the planet’s ice sheets will melt.

[Image 1] A warming planet means continuing changes in its ecosystems. As the oceans absorb more carbon dioxide, the chemistry of the ocean changes, putting many sea creatures at risk. The IPCC projects that by 2100 the pH of the ocean will drop to its lowest point in at least 20 million years.

[click, Image 2] As temperatures get milder, mosquitoes, ticks, rodents, and other disease carriers will expand their range, particularly in developing countries. Here in the U.S., dengue hemorrhagic fever, a tropical, mosquito-borne disease, hit for the first time in modern times in 2005 in the Lower Rio Grande Valley.

[click, Image 3] Warmer temperatures will also mean less snow overall at certain latitudes because more will fall as rain, and the snow that does fall will melt faster. This affects people living in areas that depend on snow-fed reservoirs for water.

[click, Image 4] The IPCC projects increases of 5-20% in crop yields in the first decades of this century. but the crops will be more prone to failure if climate variability increases and precipitation becomes less dependable. And ironically, with higher temperatures comes an increased potential for killing freezes. This is because plants start growing earlier, making them more vulnerable to sudden spring-time cold spells.

How sure are scientists?

What don’t we know?• Is there some critical piece of the about climate process we don’t understand?• How and when will our fossil fuel use change?• Will future , yet-to-be-discovered technologies mitigate the problem?• How will changing economics, global population, and political processes affect our ability to tackle the problem?

• Nothing in science is 100% certain– There are no laboratory experiments that can tell us what the future will be—

the planet IS the test tube• [click to reveal bullets] What don’t we know?

• Is there some climate process we don’t know about? So far, research over the years has strengthened the conclusion that humans are adversely influencing climate, but scientific knowledge is still evolving

• We don’t know how things might change in the future, such as• Will alternative energy sources become widely available? How soon?• Will some yet-to-be-discovered technology be able to clean CO2 out of the

air?• How will changing economics, global population, and political processes affect

our ability to tackle the problem?

The IPCC

• [Image 1] The International Panel on Climate Change, the group that produces the main reports on climate change, is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Programme in 1988.

• [click, Image 2] The IPCC process involves hundreds of scientists from about 140 countries, a variety of fields, and a range of views. Their function is to assess the latest peer-reviewed literature, [click Image 3] compare different computer model results from various sources, and to achieve consensus about where the weight of the evidence points and where uncertainties lie. And

2007 Conclusions• Warming of the climate system is unequivocal• Very high confidence that global average net effect of

human activities since 1750 one of warming • Human-caused warming over last 30 years has likely had

a visible influence on many physical and biological systems

• Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.”

• Based on the evidence accumulated over the last 40 years, these are some of their main conclusions. The words in red were very carefully chosen to reflect quantifiable estimates. So Very High Confidence and means the statement has at least a 9 out of 10 chance of being correct, Very Likely means the scientists are more than 90% sure, and Likely means they are more than 66% sure.

Consensus?• Do we know enough about the drivers of climate to know what causes change? • Are we underestimating the Earth system’s complexity ?• Can models accurately simulate the complex climate system? •Are there processes that will limit warming naturally?

On the other hand…

• Arctic sea ice melting faster than predicted.• Fossil fuel emissions exceeded most IPCC projections.• Are assumptions about global energy use are too optimistic?•How quickly can developing countries reduce GHG emissions?• Calculations don’t include unexpected melting in Greenland and Antarctica.

What do climate scientists really think?

• [Image 1] A survey conducted in 2007 by George Mason University of U.S. scientists who have expertise in climate science (not just a scientific background) what they think.

• 97% of the 489 respondents agreed that “global average temperatures have increased” during the past century. That’s up from 60% in 1991.

• [click, Image 2] 84% believe human activities are causing the warming, and only 5% disagree.

• So the survey does indicate the bulk of climate scientists—those most knowledgeable about the field—now agree that human activity contributes to global warming.

Be an educated consumer

• IPCC AR4 Synthesis Report (http://www.ipcc.ch/ipccreports/ar4-syr.htm)

• Other organizations: – NAS (http://dels.nas.edu/climatechange/)– US CCSP (http://www.climatescience.gov/)

• Look for contrasting opinions• Evaluate the source

• As with all science that affects our lives, we need to be educated consumers. Do your homework, starting with the IPCC reports. All of the reports provide interesting information, although they are lengthy and quite technical. The AR4 Synthesis Report is easy to read and provides a good summary of the other reports. Also look at the work from other authoritative sources such as the National Academies of Science and the U.S. Climate Change Science Program.

• When looking at information (particularly on the Web), search out contrasting opinions to see what others say about a topic.

• And evaluate the source—is it someone with real expertise, or just someone with an opinion.

What next—what can we do?

• Reducing our greenhouse gas emissions and our use of fossil fuels will not be easy, but it is doable. Here’s how some researchers at Princeton view it.

• Our current path is toward doubling CO2 emissions in the next 50 years, with even greater increases beyond that. In order to get off this path, we need to find ways to keep [8] emissions constant for the next 50 years and then reduce them during the second half of the century. This would [9] limit atmospheric CO2 to about 570 ppm—still greater than the roughly 380 ppm in the atmosphere today, but enough to avoid the worst predicted consequences.

• • [Image 1] In order to hold carbon emissions constant over the next 50 years, we

need to find some combination of ways to cut 8 billion tons of carbon emissions per year. In the graph, the difference between where we are and where we’d like to be forms a triangle with a height of 8 billion tons in 2055.

What next—what can we do?

Produce more fuel-efficient vehiclesReduce vehicle useImprove energy-efficiency in buildingsDevelop carbon capture and storage processesTriple nuclear powerIncrease solar powerDecrease deforestation/plant forestsImprove soil carbon management strategies

Here are examples of 8 technologies that could save 8 billion tons, or 8 wedges, of carbon. Some of these we could do right away, while others are based on technologies still being studied, such

as capturing and storing carbon.

[Details on strategies:Efficient vehicles: Double car fuel efficiency in 2055 from 30 miles per gallon (mpg) to 60 mpg

Reduced vehicle use: Halve the miles traveled by the world’s cars in 2055Efficient buildings: Cut emissions by 25% in all buildings

CCS electricity: Capture and store carbon from 800 large coal power plants or 1600 large natural gas power plants

Triple the world’s current nuclear capacitySolar electricity: Increase solar capacity 700 times

Forest storage: Halve global deforestation and double forest planting in 50 yearsSoil storage: Apply carbon management strategies to all of the world’s farm fields]

This list represents only some of the possible strategies, but choosing strategies will not be easy. However, the longer we wait to reduce emissions, the higher the target will need to be, and the more adaptation will be necessary. In 2004, when the wedges concept was first introduced, the

target was only 7 billion tons.

Individual actions

Use mass transit, bike, walk, roller

skate

Tune up your

furnaceUnplug

appliances or plug into a

power strip and switch it off

Buy water-saving appliances and

toilets; installing low-flow shower

heads.

Caulk, weatherstrip, insulate, and replace old windows

Buy products with a U.S. EPA

Energy Star label