Radiation and Climate

Greenhouse Gases and Global Change

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Can we maintain our status?• As long as concentrations of carbon dioxide and

other greenhouse gases in the atmosphere remain relatively constant, the greenhouse effect will comfortably maintain Earth’s average temperature.

• The hydrologic cycle and the carbon cycle maintain stable concentrations of water and carbon dioxide in their respective reservoirs, including the atmosphere.

• However, the effect of human activity must be considered.

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“Spiraling-Up”

• If more CO2 is added to the atmosphere than can be removed by natural processes, its concentration will increase.– If enough CO2 were added, the atmosphere could

retain enough additional IR radiation from the Sun to increase Earth’s average surface temperature.

– CO2 stored in ice, water, and the frozen floors of northern forests could also be released.

– A “spiraling-up” effect could occur, where warmer temperatures produce more carbon dioxide, which produces warmer temperatures, and so on.

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Hydrologic Cycle

• The hydrologic cycle must also be considered.– The atmosphere contains about 12 trillion metric

tons of water vapor, a quantity so large that it might seem impossible that human activity could significantly affect it.

– However, if global temperatures increase, oceans and other bodies of water will also become warmer.

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Temperature and Water Vapor

• The amount of water vapor released increases as temperature increases, so more of this slightly warmed water will evaporate, increasing the atmospheric concentration of water vapor.

• As a greenhouse gas, increased water vapor may cause an even greater increase in global temperatures due to absorption and the release of infrared radiation, which causes another “upward spiral.”

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Runaway Greenhouse Effect

• This spiraling-up effect is also commonly known as a runaway greenhouse effect.

• However, by contrast, increased water vapor concentration would also lead to increased cloud cover, which would reflect more solar radiation, thus counteracting some of the predicted temperature increase.

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Other Greenhouse Gases• Two other naturally occurring greenhouse gases

are also produced by human activity: nitrous oxide (N2O) and methane (CH4).

• Many agricultural and industrial activities, as well as the burning of solid waste and fossil fuels, contribute to the concentration build up of N2O in the atmosphere.

• CH4 occurs naturally as a decomposition product of plant and animal wastes, but it is also produced from refining fossil fuels and raising livestock.

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In addition to carbon dioxide, atmospheric gases such as nitrous oxide (N2O) and methane (CH4) are considered greenhouse gases. Raising cattle increases methane concentrations, while burning solid waste adds nitrous oxide to the

atmosphere.

http://ecoki.com/increased-

nutrients-in-organic-cows/

http://www.coldtruth.com/2009/children/risks-to-children-children/epa%E2%80%99s-studies-on-the-safety-of-shredded-tires-on-children%E2%80%99s-

playgrounds-were-actually-never-conducted/8

Non-natural Greenhouse Gases

• Some gases that do not occur naturally can also contribute to the greenhouse effect.– Especially fluorocarbons used in refrigeration and

air conditioning– See next slide for a table that shows these gases

are much more effective than CO2 in retaining heat at Earth’s surfaces.

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GREENHOUSE GAS EFFECTIVENESS

Greenhouse Gas Relative Effectiveness Percent Abundance in Troposphere

Carbon dioxide (CO2) 1 (assigned value) 3.3 x 10-2

Methane (CH4) 30 1.7 x 10-4

Nitrous oxide (N2O) 160 3 x 10-4

Water vapor (H2O) 0.1 1

Ozone (O3) 2 000 4 x 10-6

Trichlorofluoromethane (CCl3F)

21 000 2.8 x 10-8

Dichlorofluoromethane (CCl2F2)

25 000 4.8 x 10-8

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Temperature Increases

• What are implications of increased atmospheric concentrations of greenhouse gases?

• Has any effect on Earth’s climate been noted thus far?

• The 20th century’s 10 warmest years all occurred within the last 15 years of that century.– Of these, 1998 was the warmest year on record.

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Global annual mean surface air temperature trends since 1880. The 1951-1980 mean surface air temperature has been used as the zero-point base for comparison.

Graph referenced from NASA website on http://jouleblog.com/ 12

Global Warming• An international panel of climate scientists has predicted

that under a business-as-usual scenario, in which no steps are taken to control the release of human-generated CO2 and other greenhouse gases, the average global surface temperature could rise 0.8°C to 2.9°C in the next 50 years and 1.4°C to 5.8 °C in the next 100 years, with significant regional variation.

• This prediction can be compared to evidence that Earth has warmed only 3°C to 5°C since the depths of the last Ice Age, some 20 000 years ago.

• These observed and predicted increases in average global surface temperatures are often referred to as global warming.

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IPCC

• The 2001 report of the United Nations Intergovernmental Panel on Climate Change (IPCC) reported that Earth’s average global surface air temperature increased by 0.4°C to 0.8°C over the past 100 years.

• The 2000-page report was prepared by 500 climate scientists and reviewed by another 500 climate experts.

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Disagreement Among Scientists

• Although most climate specialists agree that Earth’s average temperature will increase, there is still some disagreement about causes of this predicted warming.

• New data indicate that the lower atmosphere may not be warming at the same rate as Earth’s surface, which suggests that additional factors contribute to the buildup of greenhouse gases and to the warming trend.– Ocean currents, such as El Niño and La Niña, transport

thermal energy within the oceans and can affect climates when this energy is transferred to he land and to the atmosphere.

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Possible Impact• What are the projected effects of global warming?• Based on the assumption that the average temperature increases

0.5°C per decade, the oceans are predicted to rise about 5 cm each decade over this century.– Due to the major effect of melting polar ice caps and very small

contribution of expansion of ocean water from warming– Such changes could produce an approximately 15-cm increase in

ocean levels by 2030, a situation that could cause flooding in coastal cities, such as Miami and New York.

• Possible regional climate changes, including reduced summer precipitation and soil moisture in North America, might be expected.– Northern regions might benefit from lengthened growing seasons,

while growers in southern regions would probably shift to crops that can benefit from warmer winters.

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The glacier on Mt. Kilimanjaro as photographed in February 1993 (top) and February 2003 (bottom).

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http://en.wikipedia.org/wiki/Mount_Kilimanjaro

What Can Be Done?• Scientists today understand the influence of CO2 and other greenhouse

gases on world climate better than they did even a decade ago.– Sophisticated computer modeling has enhanced their research efforts.– This new understanding supports the idea of a surface global warming trend.

• In 1992, representatives of more than 150 nations developed the Framework Convention on Climate Change, where they agreed to develop policies and procedures to reduce greenhouse gas emissions.

• In 1997, the third meeting of parties to this agreement, held in Kyoto, Japan, resulted in a protocol to address climate change.– By late 2004, 126 nations had signed the protocol; thus, this international

agreement entered into force in 2005.– As of 2005, some industrialized nations, including the United States and

Australia, still have not ratified the Kyoto Protocol.

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Kyoto Protocl

• The Kyoto Protocol sets ambitious goals for reducing greenhouse gas emissions.

• For industrialized nations, this involves developing energy-efficient technologies, relying more heavily on renewable energy, and applying alternative processes that do not release greenhouse gases into the atmosphere.

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Kyoto Protocol Examples• An alternative process has been developed for producing the

polystyrene foam used to make such items such as plastic egg cartons and meat trays.– This process uses CO2 that would normally be released during the

production of ammonia.– The captured CO2 replaces chlorofluorocarbons (CFCs) that had been

used in this foam-producing process, this reducing greenhouse gases in two ways.• First, CO2 that would normally be released by another industry is used.• Second, CO2 replaces CFCs which have a global-warming potential much

greater than that of CO2.• In an application of green chemistry principles, Hangers Cleaners, a

chain of dry-cleaning stores, also uses liquid carbon dioxide (formed by compressing the gas under high pressure) and special detergents to replace potentially harmful dry-cleaning solvents.

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HOMEWORK (review)

1) If you see considerable black exhaust emitted by a bus, what might that indicate about the combustion processes in the engine?

2) a. What would be the effect on the average global temperature if significant atmospheric increases occurred in

i. Carbon dioxide?ii. Methane?iii. Water vapor?b. How would such global temperature changes, in turn, affect Earth’s atmosphere? Explain.

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