Science of Global Climate Change Policy

General Background

Global warming is caused by emissions of carbon dioxide and other gases that trap solar heat in the earth's atmosphere instead of allowing it to radiate out into space. These gases occur naturally in our environment, and are part of the cycle by which oxygen and carbon are circulated through our ecosystem. The problem is that cycle has become unbalanced, creating carbon gases at a far faster rate than they are being absorbed back into vegetation and earth.

Carbon gasses are emitted primarily by the burning of fossil fuels to meet our energy needs and the clearing of forests for wood and farmland. The burning of fossil fuels takes carbon that had been stored under the earth and releases it into the air. The clear-cutting of forests takes carbon that was sequestered in the trees and releases it, either through burning or decay. Deforestation also removes one of the biggest converters of CO2 into oxygen, which balances the animal conversion of oxygen into CO2. Thus, deforestation is a "double whammy."

It's estimated that the rise in greenhouse gases has resulted in the rise in the average earth temperature by one degree celsius during the 21st century. One degree is not enough that we would notice it directly. However, even a small rise in the earth's temperature will drastically alter weather patterns, increasing both the frequency and intensity of violent weather such as hurricanes, floods, droughts, extreme heat waves and cold. For this reason many people believe that "global warming" is a misnomer, incorrectly giving people the impression that the earth should feel drastically warmer to them. Instead, the term "global climate change" more accurately conveys the situation.

How the Targeted Reductions Are Determined

The scientific consensus is that if the average global temperature rises more than two degrees from the start of our industrial age (circa 1860's), we will pass a point of no return. Mass species extinction will drastically reduce biodiversity. And melting of the Greenland and Arctic ice sheets will prevent their ability to reflect heat, and result in 12 to 40 foot sea level rises.

Based on that, scientists calculated that we must stabilize the concentration of greenhouse gases in the atmosphere at or below 450 parts per million CO2-equivalent (CO2 or its equivalent in other greenhouse gases). This target gives us an approximately 50% chance of keeping the global average temperature from rising more than 2°C above pre-industrial levels, and a 67% chance of keeping the rise below 3°C. To meet this target, worldwide cumulative emissions of greenhouse gases must be no more than 1,700 gigatons (Gt) CO2eq for the period between 2000 and 2050. Approximately 330 GtCO2eq has already been emitted, leaving a “global cumulative emissions budget” of 1,700 GtCO2eq.

Assuming that developing countries do not significantly industrialize further during this time (i.e., do not add more to their current greenhouse gas contributions), industrialized nations such as the U.S. will have to reduce their emissions to 70-80% below our 2000 levels by the year 2050. That is how the oft-touted target of "80 by 2050" is derived. One can see from this that:

1. It is actually a conservative target, giving us only a 50% chance of success and assuming that developing countries will not "develop."
2. The longer we wait to reduce emissions, the more drastic the reductions will have to be later.

For more in depth information on the science of global climate change, go to the Union of Concerned Scientist's pages on Global Warming Science.