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Atmosphere and Climate Change Section 3

Section 3: Global Warming

Preview

Bellringer

Objectives

The Greenhouse Effect

Measuring Carbon Dioxide in the Atmosphere

Rising Carbon Dioxide Levels

Greenhouse Gases and the Earths Temperature How Certain is Global Warming?

Modeling Global Warming


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Preview, continued

The Consequences of a Warmer Earth

Melting Ice and Rising Sea Levels

Global Weather Patterns

Human Health Problems

Agriculture

Effects on Plants

Effects on Animals


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Preview, continued

Recent Findings

Reducing the Risk


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Bellringer


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Objectives

Explainwhy Earths atmosphere is like the glass in agreenhouse.

Explainwhy carbon dioxide in the atmosphere appearsto be increasing.

Explainwhy many scientists think that the Earthsclimate may be becoming increasingly warmer.

Describewhat a warmer Earth might be like.


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The Earth is similar to a greenhouse. The Earths

atmosphere acts like the glass in a greenhouse.

Sunlight streams through the atmosphere and heats theEarth. As this heat radiates up from Earths surface,

some of it escapes into space. The rest of the heat isabsorbed by gases in the troposphere and warms theair.

This process of heat absorption is called the greenhouseeffect.


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Not every gas in our atmosphere absorbs heat in thisway.

A greenhouse gas is a gas composed of molecules thatabsorb and radiate infrared radiation from the sun.

The major greenhouse gases are water vapor, carbondioxide, CFCs, methane, and nitrous oxide. Of these,water vapor and carbon dioxide account for most of the

absorption of that occurs in the atmosphere.


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In 1985, a geochemist named Charles Keeling installedan instrument at the top of a tall tower on the volcanoMauna Loa in Hawaii. He wanted to precisely measure

the amount of carbon dioxide in the air, far away fromforests and cities.

In a forest, carbon dioxide levels rise and fall with the

daily rhythms of photosynthesis. Near cities, carbondioxide from traffic and industrial pollution raises thelocal concentration of gas.


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The winds that blow steadily over Mauna Loa have comethousands of miles across the Pacific Ocean, far frommost forests and human activities, swirling and mixing as

they traveled.

Keeling reasoned that at Mauna Loa, the averagecarbon dioxide levels for the entire Earth could be

measured.


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Keelings first measurement, in March of 1958, was

0.0314 percent, and the levels rose slightly the nextmonth. By summer the levels were falling, but in the

winter, they rose again.

During the summer, growing plants use more carbondioxide for photosynthesis than they release inrespiration, causing the levels to drop.

In the winter, dying grasses and fallen leaves decay andrelease the carbon that was stored in them, causinglevels to rise.


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After a few years of measurement, it was obvious thatthe levels were undergoing changes other than seasonalfluctuations.

Each year, the high carbon dioxide levels of winter werehigher, and each year, the summer levels did not fall aslow.

In 42 years, carbon dioxide has gone from 314 to 386parts per million, and increase of 54 parts per million.This increase may be due to the burning of fossil fuels.


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Greenhouse Gases and the Earths

Temperature Many scientists think that because greenhouse gases

trap heat near the Earths surface, more greenhouse

gases in the atmosphere will result in an increase in

global temperature.

A comparison of carbon dioxide in the atmosphere andaverage global temperatures for the past 400,00 years

support that view.


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Greenhouse Gases and the Earths

Temperature Today, we are releasing more carbon dioxide than any

other greenhouse gas into the atmosphere.

Millions of tons of carbon dioxide are released into theatmosphere each year from power plants that burn coalor oil, and cars that burn gasoline. Millions of trees areburned in tropical rainforest to clear the land for farming.

We also release other greenhouse gases, such asCFCs, methane, and nitrous oxide, in significantamounts.


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Greenhouse Gases


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How Certain is Global Warming?

Global warmingis a gradual increase in the averageglobal temperature that is due to a higher concentrationof gases such as carbon dioxide in the atmosphere.

Earths average global temperature increased during the

20th century and many scientists predict that thiswarming trend will continue throughout the 21st century.


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How Certain is Global Warming


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How Certain is Global Warming?

However, not all scientists agree that the observedglobal warming is due to greenhouse gases.

Some scientists believe that the warming is part ofnatural climatic variability.

They point out that widespread fluctuations intemperature have occurred throughout geological time.


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Scientists are currently unable to make accuratepredictions about the rate of global warming becauseclimatic patterns are too complex and too many variablesmust be taken into account to be solved, even using

todays fastest computers.

Predictions about climate change are based oncomputer models that predict how phenomena such astemperature, rainfall patterns, and sea level will be

affected.


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Computer modeling is complicated by the Earthsfeedback processes that sometimes make it necessaryto use different equations under changing simulatedenvironments.

These feedback processes are related to things such asclouds, water vapor, ice, changes in ocean chemistry,and changes in vegetation.

Computer models are becoming more reliable as moredata are available, additional factors are considered, andfaster computers are built.


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The Consequences of a Warmer Earth

The impacts of global warming could include a numberof potentially serious environmental problems.

These problems range from the disruption of globalweather patterns and a global rise in sea level toadverse impacts on human health, agriculture, andanimal and plant populations.

Other impacts on the environment that could not bepredicted by computer models might also arise.


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Melting Ice and Rising Sea Levels

If the global temperature increased, the amount of iceand snow at the poles would decrease, causing sealevels around the world to rise.

Coastal wetlands, and other low-lying areas could beflooded. People who live near coastlines could lose theirhomes and sources of income.

The salinity of bays and estuaries might increase,adversely affecting marine fisheries. Also, freshwateraquifers could become too salty to be used as sources offresh water.


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Global Weather Patterns

If the Earth warms up significantly, the surface of theoceans will absorb more heat, which may makehurricanes and typhoons more common.

Some scientists are concerned that global warming willalso cause a change in ocean current patterns, shuttingoff the Gulf Stream.

Such a change could significantly affect the worlds

weather. Severe flooding could occur in some regions atthe same time droughts devastate other regions.


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Human Health Problems

Greater numbers of heat related deaths could occur.Very young and very old people would have the greatestrisk of heat exhaustion.

Concentrations of ground level ozone could increase asair temperatures rise, causing respiratory illnesses,especially in urban areas, to increase.

Warmer temperatures might enable mosquitoes, whichcarry diseases such as malaria and encephalitis, togreatly increase in number.

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Agriculture

Agriculture would be most severely impacted by globalwarming if extreme weather events, such as drought,became more frequent.

Higher temperatures could result in decreased cropyields.

As a result, the demand for irrigation could increase,which would further deplete aquifers that have alreadybeen overused.

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Effects on Plants

Climate change could alter the range of plant speciesand could change the composition of plant communities.

A warmer climate could cause trees to colonizenorthward into cooler areas.

Forests could shrink in areas in the southern part of theirrange and lose diversity.

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Effects on Animals

Global warming could cause a shift in the geographicalrange of some animals. For example, Northern birdsmay not migrate as far south during the winter.

Warming of surface waters of the ocean might cause areduction of zooplankton, tiny shrimp-like animals, thatmany marine animals depend on for food.

Warming tropical waters may kill algae that nourishcorals, thus destroying coral reefs.



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Recent Findings

The International Panel on Climate Change (IPCC)issued its Third Assessment Report (TAR) in 2001 thatdescribed what was currently known about about theglobal climate system and provided future estimates

about the state of the global climate system. The IPCC reported that the average global surface

temperature increased by 0.6C during the 20th century,snow and ice cover has dropped, and the global sea

level has risen.



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Recent Findings

The IPCC also reported that concentrations ofatmospheric gases have continued to increase as aresult of human activities.

It has also predicted that human influences will continueto change the composition of the Earths atmosphere

and continue to warm the Earth throughout the 21stcentury.



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Reducing the Risk

The Kyoto Protocol is an international treaty accordingto which developed countries that signed the treatyagree to reduce their emissions of carbon dioxide andother gases that may contribute to global warming by the

year 2012. In March of 2001, the United States decided not to ratify

the Kyoto Protocol. However, most other developednations are going ahead with the treaty.



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Reducing the Risk

The need to slow global warming has been recognizedby the global community. Some nations andorganizations have engaged in reforestation projects toreduce carbon dioxide.

However, the attempt to slow global warming is madedifficult by the economic, political, and social factorsfaced by different countries.



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Reducing the Risk

Conflict has already arisen between developed anddeveloping countries over future CO2 emissions.

Developing countries are projected to make up half of allCO2 emissions by 2035.



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Reducing the Risk



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