Environment - Global Climate Change

Global Climate Change

Climate Change Facts
September 18, 1997

Issue 2 U.S. House of Representatives

Minority Staff, Committee on Government Reform and Oversight

The Relationship Between Carbon Dioxide Levels and Global Temperatures
As explained in the last fact sheet, the greenhouse effect is caused by carbon dioxide and other greenhouse gases that accumulate in the atmosphere and trap heat. Historically, levels of carbon dioxide (CO2) in the atmosphere have correlated closely with global temperatures. This fact sheet describes this relationship between carbon dioxide and temperature. The next fact sheet will discuss whether increased CO2 levels have caused warming to begin.

Ice Core Records. The longest record of global temperature comes from ancient ice core samples that date back 200,000 years. Scientists sample air bubbles that are trapped in the ice and can measure the ratio of isotopes to determine atmospheric temperature and CO2 concentrations. Although CO2 is just one of several greenhouse gases, it contributes over half of the radiative forcing that causes warming, and serves as an indicator of the relationship between greenhouse gas concentrations and temperature.

Ice core samples show that prehistoric changes in carbon dioxide levels correlate strongly with changes in climate. Core samples from Antarctica show that temperature and CO2 levels both rose as an ice age ended 130,000 years ago. They then fluctuated similarly, dropping at the onset of a new glacial period, and rising again as the ice retreated about 10,000 years ago. The chart on the reverse of this page depicts the relationship.

CO2 Concentration Trends. Concentrations of CO2 changed over the last 200,000 years, but have risen abruptly in the past two hundred years. Carbon dioxide levels appear to have varied by less than 10% during the 10,000 years prior to industrialization. The ancient record of carbon dioxide in the atmosphere demonstrates that CO2 concentrations remained between 190 and 280 parts per million by volume (ppmv) over the past 100,000 years.

Current CO2 concentrations are 360 ppmv, higher than anything seen in the past 200,000 years. Over the past 200 years, CO2 levels have risen by about 30%. By the end of the 19th Century, CO2 concentrations were near 300 parts per million. According to the Intergovernmental Panel on Climate Change, an international, peer-reviewed scientific body assembled by the United Nations and the World Meteorological Organization, "[t]he anthropogenic emissions of these gases have contributed about 80% of the additional climate forcing due to greenhouse gases since pre-industrial times. The contribution of CO2 is about 60% of this forcing."

The chart demonstrates the recent, abrupt rise in CO2 and temperature. Although CO2 occurs naturally in the atmosphere, burning of coal, oil, and natural gas has released carbon stored in these fossil fuels. Land use changes from urbanization also contribute CO2 as deforestation releases carbon stored in trees. Each year, approximately 7 billion tons of carbon are released into the atmosphere worldwide, substantially increasing the rate of accumulation of greenhouse gases that cause warming. According to the IPCC, increasing levels of CO2 in the atmosphere "will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface." The next fact sheet will discuss whether global warming has already begun.