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Global WarmingGlobal Warming

Greenhouse Gases and Climate


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Is the climate becoming warmer and warmer?

According to the National Academy of Sciences, the Earth'ssurface 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)


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

temperature in upper levels may be different, even reversed.


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W hat cause the temperature of the atmosphere to go up?

There are many possible mechanisms that can cause thewarming of the atmosphere, for example: N atural 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..


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The real greenhouse


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The (Atmospheric) G reenhouse Effect

Ex amples of greenhouse gases: H 2O, CO 2, CH 4, CFC.Currently, CO 2 is the main suspect of causing the global warming since the20 th century because combustion of fossil fuel naturally injects CO 2 intothe atmosphere and it has increased dramatically since last century.

Remember this chart?


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Atmospheric Carbon DioxideThis 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 beenfound in many other places.


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S outh Pole and Barrow, Alaska,show the same trend as Hawaii


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How is the CO 2 increaseconnected 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 2 concentration inthe atmosphere may cause warming.


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Feedback EffectThe climate system is very complicated. A change in onecomponent of the system may cause changes in other components. S ometimes the changes in other components

enhance 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 exist inthe climate system. In studying the global climatic change,we cannot make conclusions based on intuition, but haveto take all such possible complicated effects into account.A good climate model would have treated all of themrealistically.


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An example of positive feedback W hen 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 2into 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.


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An example of negative feedback Consider a clear region over the ocean. S ince there is nocloud, the sun shines on the ocean surface, causing it towarm up. This makes this part of the ocean warmer thanother 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.


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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.


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Projection of future warming

Vertical distribution of temperature in radiative-convective equilibrium for various values ofatmospheric CO 2 concentration, i.e., 150, 300, and600 ppm by volume. From Manabe and Wetherald(8).


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

Source: IPCC


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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 changesin the animal and humanworld in response to theseenvironmental changes.

Source: NOAA


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Ice shelves of the S outh Pole have partly separated and are collapsing.(NA S A)

Receding high mountain glaciers

Melting ice and

rising sea level


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Of course the physical environmentalchange will lead to changes in the

biosphere including our society.


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Not everybody is convinced of the greenhouse

gases - global warming theoryAt this point, it appears that thewarming itself is real the surfacetemperature indeed becomes higher in the last few decades.The question is Is the warming

caused by the greenhouse gases(especially CO 2)?S ome 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).

Su mmaryWorld leaders gathered in Kyoto, Japan, inDecember 1997 to consider a world treatyrestricting emissions of ''greenhouse gases,''chiefly carbon dioxide (CO 2), that arethought to cause ''global warming'' severe

increases in Earth's atmospheric andsurface temperatures, with disastrousenvironmental consequences. Predictions ofglobal warming are based on computerclimate modeling, a branch of science still inits infancy. The empirical evidence actualmeasurements of Earth's temperatureshows no man-made warming trend. Indeed,over the past two decades, when CO2 levelshave been at their highest, global averagetemperatures have actually cooled slightly.

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

Y ou can get IPCC re ports at htt p://www.i pcc.ch/


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S ome examples of criticismsThere are evidence showing thatthe current temperature isnt reallythat warm compared to what wastwo to three thousand years ago.The figure to the right shows thatthe temperature of S agaso S eafluctuates 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)


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There are also evidence showing that the solar activity seemsto have some influence on atmospheric temperature. But thereare many questions here. Especially on how and how much.


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G lobal W arming: More than a scientific problem - Aside fromscientific problems, there are political problems as well.

At Climate Meeting, Unlikely Ally for Have-Nots

By AMY WALDMANN ew York Times 1 N ov 2002

N EW DELHI, Friday, N ov. 1 WhenIndia's prime minister, Atal Bihari Vajpayee,finished speaking at the internationalconference on climate here on Wednesday,

the fissure between richer and poorercountries over how best to tackle globalwarming could no longer be papered over.In his speech, he argued that poorercountries could not be expected to investmoney in tackling the causes of globalwarming. They bear little responsibility, hesaid, producing fewer greenhouse gasesthan industrialized countries, and yet have

been hit harder by the natural calamities,from drought to floods, caused by climatechanges. They have weaker economies,and with pressing needs in everything fromhealth to education, can little afford to investin clean-air technologies.

His speech articulated sentiments resentments, in some cases widelyshared among developing nations. So whileit produced little new of substance, theconference, the eighth since the UnitedN ations Framework Convention on ClimateChange was adopted in 1992, illuminatedthe challenges in crafting a global responseto global warming.

It highlighted a divide between north andsouth, between the industrialized anddeveloping worlds, over who should bear theobligations and burdens of trying to reducethe emissions that cause global warming.But on several points, the south found itselfwith an unlikely ally: the United States,which under the Bush administration hasalso blanched at joining efforts to reduceemissions.Instead, the United States joined India andother developing countries in encouraging afocus on developing the technology andfinding the resources to adapt to climatechange.


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Y ou 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);870872.


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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 theresults of natural fluctuation of the global climate system.

Recently, there seems to be increasing evidence showing theconnection 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.


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MRS.RANJANA SALUJA DIKSHA & SNEHA

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