Greenhouse Gases and Climate

8/8/2019 Greenhouse Gases and Climate

1/25

Global WarmingGlobal Warming

Greenhouse Gases and Climate

[email protected]


2/25

Is the climate becoming warmer

and warmer? According to the National Academy of Sciences, the Earth's

surface temperature has risen by about 1 degree Fahrenheit inthe past century, with accelerated warming during the past two

decades. There is new and stronger evidence that most of thewarming over the last 50 years is attributable to humanactivities. Human activities have altered the chemicalcomposition of the atmosphere through the buildup of greenhouse gases primarily carbon dioxide, methane, andnitrous oxide. The heat-trapping property of these gases isundisputed although uncertainties exist about exactly how

earth's climate responds to them . (source:US-EPA)

[email protected]


3/25

Global temperature trend Note that these are surface temperatures and mostly overland. The

temperature in upper levels may be different, even reversed.

[email protected]


4/25

[email protected]


5/25

What cause the temperature of

the atmosphere to go up? There are many possible mechanisms that can cause the

warming of the atmosphere, for example: Natural variation the climate becomes warmer by internal chaotic

dynamics of the earth-atmosphere system (that is, no external influence). Solar activity either direct increase of solar energy output or indirect

trigger mechanisms due to solar activity (though nobody knows how)may cause the surface temperature to go up.

Greenhouse effect increasing greenhouse gases such as CO 2, CH 4,

NO, CFC,etc. (actually H 2O is very efficient, too, but at present it isassumed to be in steady state).

The last one is presently thought to be the most likely cause of theglobal warming and hence we will examine it here in this chapter..

[email protected]


6/25

The real greenhouse

[email protected]


7/25

The (Atmospheric) Greenhouse Effect

Examples of greenhouse gases: H 2O, CO 2, CH 4, CFC.

Currently, CO 2 is the main suspect of causing the global warming since the 20 th century because combustion of fossil fuel naturally injects CO 2 into the atmosphereand it has increased dramatically since last century.

Remember this chart?

[email protected]


8/25

Atmospheric Carbon Dioxide This chart shows a steady increase of CO 2 concentration in the last five decades.

Although this chart is based on Mauna Loas data, the same trend has been found inmany other places.

[email protected]


9/25

South Pole and Barrow, Alaska,

show the same trend as Hawaii

[email protected]


10/25

How is the CO 2 increase

connected to the global warming? Physically, via the greenhouse effect.

The connection is usually made via the use of aclimate model .

Control run versus scenarios.

If the scenario run results show warmer surfacecondition than the control, then it is plausible tosuspect that the increasing CO 2concentration in theatmosphere may cause warming.

[email protected]


11/25

Feedback Effect The climate system is very complicated. A change in one

component of the system may cause changes in other components. Sometimes the changes in other componentsenhance the initial change, then we say that these changeshave positive feedback to the system. If the changes resultin the reduction of the original change, then they havenegative feedback .

Both positive and negative feedback processes may existin the climate system. In studying the global climaticchange, we cannot make conclusions based on intuition,

but have to take all such possible complicated effects intoaccount. A good climate model would have treated all of them realistically.

[email protected]


12/25

An example of positive feedback

When the climate becomes warmer (either due tothe increase of CO 2 in the atmosphere or other

unknown mechanisms), the ocean may also become warmer. A warmer ocean has lower solubility of CO 2 and hence will release more CO 2 into the atmosphere. This may cause the climate to

become even warmer than before. Thus thedependence of solubility of CO 2 on temperaturehas a positive feedback on the climate system.

[email protected]


13/25

An example of negative feedback

Consider a clear region over the ocean. Since there is nocloud, the sun shines on the ocean surface, causing it towarm up. This makes this part of the ocean warmer than

other parts and the air over it tends to rise (causingconvection). As we have learned before, rising air expandsand cools, causing clouds to form. The formation of cloudswill block out the sun and the solar heating of the oceansurface will cease. The surface will start to cool down.

Thus the cloud formation due to surface heating andconvection is a negative feedback to the climate system.

[email protected]


14/25

How fast will the CO 2 concentration increase?

There are various estimates of the CO 2 increasing rate. They aredifferent in the statistical models used (for example, linear vs.nonlinear increase) and the future regulations.

[email protected]


15/25

Projection of future warming

Vertical distribution of temperature inradiative-convective equilibrium for variousvalues of atmospheric CO 2 concentration, i.e.,150, 300, and 600 ppm by volume. FromManabe and Wetherald (8).

[email protected]


16/25

The degree of warming will not be uniform everywherehigher latitudes are more sensitive

Source: IPCC [email protected]


17/25

If temperature can change, so do other meteorological andenvironmental variables.

The change intemperature may cause achange in precipitation.

Vegetation may alsochange in response totemperature and

precipitation changes. And there will be changes

in the animal and humanworld in response to theseenvironmental changes.

Source: [email protected]


18/25

Ice shelves of the South Pole have partly separated and are collapsing.(NASA)

Receding high mountain glaciers

Melting ice andrising sea level

[email protected]


19/25

Of course the physical environmentalchange will lead to changes in the

biosphere including our [email protected]


20/25

Not everybody is convinced of thegreenhouse gases - global warming theory

At this point, it appears that thewarming itself is real the surfacetemperature indeed becomes higher in the last few decades.

The question is Is the warmingcaused by the greenhouse gases(especially CO 2)?

Some groups, especially the IPCCmembers argue strongly for it. But

there are other groups that are notconvinced. The summary to theright is from Robinson et al.(1998).

SummaryWorld leaders gathered in Kyoto, Japan,in December 1997 to consider a worldtreaty restricting emissions of ''greenhouse gases,'' chiefly carbondioxide (CO 2), that are thought to cause''global warming'' severe increases inEarth's atmospheric and surfacetemperatures, with disastrousenvironmental consequences.Predictions of global warming arebased on computer climate modeling, abranch of science still in its infancy.

The empirical evidence actualmeasurements of Earth's temperatureshows no man-made warming trend.Indeed, over the past two decades,when CO2 levels have been at theirhighest, global average temperatureshave actually cooled slightly.

You can get this from the following websitehttp://www.oism.org/pproject/review.pdf

You can get IPCC reports at http://www.ipcc.ch/

[email protected]


21/25

Some examples of criticisms There are evidence showing that

the current temperature isnt reallythat warm compared to what wastwo to three thousand years ago.The figure to the right shows thatthe temperature of Sagaso Seafluctuates in a range of ~ 3.6C.

Also the trend depends on thedata sets and the section of datayou select to examine see thelower chart. By using a differentdata set (here the satellitemicrowave sounding) and selectinga suitable section (for example,1978-1998) you can actually showthat there was a cooling, notwarming.

Source: Robinson et al. (1998)[email protected]


22/25

There are also evidence showing that the solar activity seemsto have some influence on atmospheric temperature. But

there are many questions here. Especially on how and howmuch.

[email protected]


23/25

Global Warming: More than a scientific problem - Aside fromscientific problems, there are political problems as well.

At Climate Meeting, Unlikely Ally forHave-Nots

By AMY WALDMANNew York Times 1 Nov 2002

NEW DELHI, Friday, Nov. 1 WhenIndia's prime minister, Atal BihariVajpayee, finished speaking at theinternational conference on climate hereon Wednesday, the fissure between richerand poorer countries over how best totackle global warming could no longer bepapered over.In his speech, he argued that poorercountries could not be expected to investmoney in tackling the causes of globalwarming. They bear little responsibility,he said, producing fewer greenhousegases than industrialized countries, andyet have been hit harder by the natural

calamities, from drought to floods, causedby climate changes. They have weakereconomies, and with pressing needs ineverything from health to education, canlittle afford to invest in clean-airtechnologies.

His speech articulated sentiments

resentments, in some cases widelyshared among developing nations. Sowhile it produced little new of substance, the conference, the eighthsince the United Nations FrameworkConvention on Climate Change wasadopted in 1992, illuminated thechallenges in crafting a global responseto global warming.

It highlighted a divide between northand south, between the industrializedand developing worlds, over who shouldbear the obligations and burdens of trying to reduce the emissions thatcause global warming.But on several points, the south founditself with an unlikely ally: the UnitedStates, which under the Bush

administration has also blanched at joining efforts to reduce emissions.Instead, the United States joined Indiaand other developing countries inencouraging a focus on developing thetechnology and finding the resources toadapt to climate change.

[email protected]


24/25

You can go back even further

Back even further intime, the CO 2 level in

the atmospherefluctuatedconsiderably andsometimes the

concentration might bemuch greater than it isnow.

Crowley & Berner, Science 2001;292(5518);[email protected]


25/25

Ultimately

The problem really is that we dont know how the climatemachine works, hence it is difficult at present to say that thewarming is due to the increase of greenhouse gases and not the

results of natural fluctuation of the global climate system. Recently, there seems to be increasing evidence showing the

connection between the global warming and industrial injectionof greenhouse gases. However, the extent is still not clear.

Hopefully, with more research we can say more definitely in thenear future.

[email protected]

Greenhouse Gases and Climate

Documents

Transcript of Greenhouse Gases and Climate