The Facts About Global Warming

Whether you were the first among everyone you know to see An Inconvenient Truth, or it still hasn't made it to the top of your Netflix queue, as a refresher, we've distilled critical facts about global warming, or in the words of Al Gore, the most serious crisis mankind has ever faced, into ten need-to-know facts — minus the PowerPoint presentation.

1. The Basics

Global warming is an increase in the earth's air and ocean temperature. Almost sounds simple when put that way, doesn't it? Keep in mind that while "weather" refers to short-term, atmospheric conditions of a small geographic area, "climate" refers to the long-term atmospheric conditions of broader geographic regions. When we talk about global warming, we're discussing climate change — a week of exceptionally hot days is not an indication of global warming, it's just abnormally warm weather.

2. Key Culprit: Greenhouse Gases

In a phenomenon known as the greenhouse effect, about 30 percent of the sun's energy bounces off the earth's surface and reflects back into space where atmospheric gases such as carbon dioxide (CO2), methane gas, and water vapor can absorb the energy, trapping heat at the earth's surface. The greenhouse effect gets a bum rap, but it's actually what keeps the earth warm enough to be inhabitable.

Problems arise when human activity generates a greater concentration of greenhouse gases like CO2 and methane in the atmosphere, leading to an overall warming effect. Major sources of human-generated CO2 emissions range from the coal-burning power plants that keep our electricity running to the cars we drive during our daily commutes. Since pre-industrial times, the concentration of atmospheric CO2 has increased 31 percent and agricultural activities such as raising cattle has caused atmospheric methane concentrations to rise 151 percent, according to the Union of Concerned Scientists. While the US is responsible for approximately 25 percent of the world's greenhouse gas emissions, countries such as India and China will likely exceed the US and Europe in emissions in the near future, according to the PEW Center on Global Climate Change.

3. A Hot Trend

The earth's average temperature has risen more than one degree Fahrenheit since 1900 — that may not sound like much, but in the scheme of things it's a lot. And the warming seems to have picked up its pace: The 11 hottest years on record all occurred within the last 13 years.

4. Humanity's Role

Though global temperature records are only one piece of the climate picture and there is some debate regarding the cycles of climate change, many scientists are now in agreement that CO2 emissions from such human activities as fossil fuel burning and land clearing are causing climate change. In 2001, the Intergovernmental Panel on Climate Change reported that "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities." And on May 29, 2008, the Bush Administration, despite its longstanding opposition to the Kyoto Protocol, released a report that conceded "most of the recent global warming is very likely due to human-generated increases in greenhouse-gas concentrations."

5. Degrees of Separation

A one-degree temperature increase may not sound like cause for concern, but the impact of even seemingly minor climate changes, no matter how gradual, is huge. Warmer temperatures can lead to extreme weather patterns — affecting agriculture and crop yields, melting glaciers, raising sea levels, causing severe droughts and expanding the reach of food-, water-, and insect-borne diseases such as West Nile virus, Lyme disease, malaria and dengue fever.