What Is Global Warming?

Posted: 22-Nov-2005; Updated: 16-Aug-2007

Global warming refers to a long-term rise in global average temperature. More specifically, the ongoing rise in temperature that started a century ago and is believed to be caused mainly by pollution from human activities, including the burning of fossil fuels and deforestation. Rising temperatures have already resulted in an increase in extreme weather events, loss of sea ice and glaciers, rising sea level, and harm to wildlife. But it is not too late to take action. A sharp reduction of greenhouse gas pollution would significantly slow global warming and reduce the likelihood of dangerous and irreversible impacts.

The Greenhouse Effect is what keeps Earth warm enough for people to live on, but a build-up in the gases that produce this warmth is overheating our planet and causing global warming. (Click here to see larger image. SOURCE: EPA.gov. )

How does global warming occur?

Heat from the sun is trapped at the Earth's surface by a blanket of greenhouse gases. This "greenhouse effect" keeps the Earth warmer than it otherwise would be. Human activities are rapidly increasing the amount of greenhouse gases in the atmosphere, causing more heat to be trapped and increasing global temperatures. The burning of fossil fuels (coal, oil, and natural gas) and land-use changes such as deforestation have raised the amount of carbon dioxide, the most important human-produced greenhouse gas, by 30% since pre-industrial times. Concentrations of methane, another potent greenhouse gas, have more than doubled. Climate scientists around the world agree that global average temperature has risen about 1°F (0.6°C) over the past century. Current temperatures are likely the warmest seen in the last 2,000 years. Assessments by the U.S. National Academy of Sciences and the United Nations Intergovernmental Panel on Climate Change (IPCC) find that most of the warming of the past 50 years is likely due to human-produced greenhouse gas pollution.

How much global warming is predicted for the future?

Scientists predict that in the absence of policies to cut greenhouse gas pollution, the Earth will heat up by 2–10°F (1-6°C) over the next century, more quickly than at any other time in the history of civilization. The difference in global average temperature between modern times and the last ice age—when much of Canada and the northern U.S. was covered with a thick ice sheet—was only about 9°F (5°C). A future rise in temperature greater than 4°F (2°C) could have dangerous and irreversible effects on the planet, such as the disintegration of ice sheets on Greenland and Antarctica and the resulting inundation of coastal cities. Action is needed now to prevent these kinds of dangerous impacts in the future.