What is Global Climate Change?

Global climate change is one of the world’s most serious and complex challenges. It is the destabilization of the earth’s climate system caused by an increase in the concentration of greenhouse gases (GHGs) in the atmosphere (see box 3). These gases absorb infrared radiation as it is reflected from the earth’s surface, acting like a blanket, trapping heat, and keeping the earth warm. The earth’s atmosphere has always contained GHGs, which in fact keep our planet about 30 degrees C (54 degrees F) warmer than it would be otherwise. However, since the beginning of the Industrial Revolution, the levels of GHGs in the atmosphere have grown rapidly as a result of human activities, particularly the burning of fossil fuels like coal, oil, and natural gas as an energy source. The current concentrations of GHGs in the atmosphere are at levels unprecedented in at least the last 650,000 years(1) and as a result, the earth’s climate is warming.

The most significant GHG is carbon dioxide (CO2), which makes up approximately 77 percent of global GHG emissions (see figure 1). One-third of those emissions result from electricity generation and heat (see figure 2). Since the beginning of the Industrial Revolution, atmospheric concentrations of CO2 emissions have increased by 35 percent,(2) primarily the result of the burning of fossil fuels and deforestation.

This increase in atmospheric CO2 and other GHG concentrations is causing the temperature of the earth’s surface and its lower atmosphere to warm at rates beyond natural variability. According to a 2001 report by the Intergovernmental Panel on Climate Change (IPCC),(3) if the current emission trends continue, by 2100 the earth’s global surface air temperatures are projected to warm by 1.4 to 5.8 degrees C (2.5 to 10.4 degrees F).(4)

While a global temperature rise of a few degrees may not seem serious at fi rst, most scientists expect this increase to have a severe destabilizing effect on the earth’s climate system, producing an array of negative social, economic, and health effects that would result from rising sea levels, intensified weather events, droughts, habitat destruction and other climate change impacts.

Global climate change is also a long-term problem, as CO2 and other GHG emissions can remain in the atmosphere for decades to centuries and even longer.(5) Consequently, because the potential impacts of climate change are likely to escalate over time as gases continue to accumulate in the atmosphere, it is imperative that steps to reduce emissions begin immediately. To prevent global temperatures from rising more than 2 degrees C (3.6 degrees F) above preindustrial levels – a level that still may have dangerous implications – global emissions must be reduced 40 to 45 percent below 1990 levels by 2050.(6)

To accomplish this, action must begin now, with the participation of all sectors of society.

Notes

1. European Project for Ice Coring in Antarctica (EPICA), “Stable Carbon Cycle–Climate Relationship during the Late Pleistocene” and “Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores,” Science, November 25, 2005.

2. A. Neftel et al., “Historical CO2 Record from the Siple Station Ice Core” (Bern: Physics Institute, University of Bern, 1994); C.D. Keeling and T.P. Whorf, “Atmospheric CO2 Concentrations (ppmv) Derived from In Situ Air Samples Collected at Mauna Loa Observatory, Hawaii” (Scripps Institute of Oceanography, 2005).

3. The IPCC was established by the World Meteorological Organization (WMO) and the United Nations Environmental Program (UNEP). It consists of approximately 2,000 of the world’s leading scientists and economists who research and issue peer-reviewed reports on climate change.

4. Intergovernmental Panel on Climate Change (IPCC), “Climate Change 2001: Impacts, Adaptation, and Vulnerability (Summary for Policy Makers)” and “Climate Change 2001: The Scientific Basis.”

5. IPCC, “Climate Change 2001: The Scientific Basis (Summary for Policy Makers).”

6. Such an emissions reduction would achieve a 2 degrees C target with a probability exceeding 85 percent. The reduction fi gure excludes emissions from changes in land use and forestry. Signifi cant climate damages may still be associated with a 2 degrees C increase in global temperatures. See M. G. den Elzen and M. Meinshausen, “Meeting the EU 2 degrees C Climate Target: Global and Regional Emissions Implications”(Bilthoven: Netherlands Environmental Assessment Agency, 2005).