Climate Change

Climate change projections are fraught with much uncertainty in regard to both the rate and magnitude of temperature and precipitation alterations in the coming decades. This uncertainty derives from a lack of precise knowledge of how climate system processes will change and of how population growth, economic and technological development, and land use will proceed in the coming century (Intergovernmental Panel on Climate Change [IPCC], 2000, 2001).

Nevertheless, three points regarding climate change can be made with some certainty (Figure 10.1). First, greenhouse gas concentrations have increased progressively since the beginning of the Industrial Revolution. Second, the natural presence of greenhouse gases is known to affect the planetary energy balance, causing the planet to be warmer than it would be otherwise. Thus, any increases in greenhouse gases will tend to enhance the natural "greenhouse effect." Third, the planet has indeed been warming over the last century, especially in the most recent two and a half decades.

The IPCC has attributed the observed warming over the last century to anthropogenic emissions of greenhouse gases, especially carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) (IPCC, 2001). Thus, anthropogenic emissions of greenhouse gases appear to be altering our planetary energy balance and to be manifested in a large-scale warming of the planet. If warming continues at the global scale, the association among greenhouse gas emissions, greenhouse effect, and surface warming will trend toward greater and greater certainty. The ultimate significance of the climate change issue is related to its planetary scale.

Solar radiation passes through the clear atmospheri

Some solar radiation Is reflected by the Earth and the atmosphere.

Some solar radiation Is reflected by the Earth and the atmosphere.

ATMOSPHERE

Some of the Infrared radiation passes through the atmosphere, and some is absorbed ane re-emitted in all directions by greenhouse gas molecules. The effect of this is to warm the Earth's surface and the lower atmosphere.

ATMOSPHERE

Most radiation is absorbed by the Earth's surface and warms it.

Most radiation is absorbed by the Earth's surface and warms it.

Infrared radiation emitted from the Earth's surface.

Infrared radiation emitted from the Earth's surface.

Carbon Dioxide Concentrations

370 360 350 340 330 320 310 300 290

Ice Core Data

Mauna Loa (Hawaii)

1860 1880 1900 1920 1940 1960 1980 2000

13.5

Global Average Temperature

5 year average

57.92 57.74 57.56 57.38 57.20 57.02 56.84 56.66 56.48 56.30

1860 1880 1900 1920 1940 1960 1980 2000

Figure 10.1 (opposite page) The three certainties of global climate change: (A) the greenhouse effect and planetary energy balance; (B) atmospheric concentrations of greenhouse gases, 1860 to present; and (C) mean global surface temperature, 1860 to present. (From OSTP. 1997. Climate Change: State of Knowledge. Office of Science and Technology Policy, Washington, DC.)

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