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Overview | Background

This section offers scientific information and data on climate change in the past and projections for the future. Specific information about the U.S. government’s role in conducting and evaluating science as well as EPA’s role in these efforts can be found on the Climate Change Science Program and EPA Research and Assessment pages in the Policy section.

Overview

Climate change refers to any significant change in measures of climate (such as temperature, precipitation or wind) lasting for an extended period (decades or longer). For full definitions of “climate change” and “global warming,” see the Basic Information page.

As through much of its history, the Earth’s climate is changing. Right now it is getting warmer. Most of the warming in recent decades is very likely1 the result of human activities (IPCC, 2007). The National Oceanic and Atmospheric Administration’s (NOAA) State of the Climate Report and the National Aeronautics and Space Administration’s (NASA) Surface Temperature Analysis indicate the average temperature of the Earth’s surface has increased by about 1.2 to 1.4ºF since 1900. Other aspects of the climate are also changing such as precipitation patterns and storminess.

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Background

Figure 1: The Greenhouse Effect
Energy from the Sun drives the Earth’s weather and climate. The Earth absorbs energy from the Sun, and also radiates energy back into space. However, much of this energy going back to space is absorbed by “greenhouse” gases in the atmosphere (see Figure 1 of Greenhouse Effect). Because the atmosphere then radiates most of this energy back to the Earth’s surface, our planet is warmer than it would be if the atmosphere did not contain these gases. Without this natural “greenhouse effect,” temperatures would be about 60ºF lower than they are now, and life as we know it today would not be possible.

During the past century humans have substantially added to the amount of greenhouse gases in the atmosphere by burning fossil fuels such as coal, natural gas, oil and gasoline to power our cars, factories, utilities and appliances. The added gases — primarily carbon dioxide and methane — are enhancing the natural greenhouse effect, and likely contributing to an increase in global average temperature and related climate changes.

The sections that follow will describe:

Past Climate Change: What has caused the Earth’s climate to change throughout its history? How has it changed?
Recent Climate Change: How has the climate changed in the last 100-150 years? What has caused the changes?
Future Climate Change: How might climate change over the next 100 years and why?
State of Knowledge: What aspects of climate change do we understand best? What are the most significant uncertainties?
The information on these pages is drawn primarily from consensus documents that include assessments of the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Global Change Research Program. Data described and illustrated originate from the monitoring and analysis of NOAA, NASA and the Department of Energy. More information.

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References

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning (eds.)]
1Throughout the science section of this website, use of “very likely” conveys a 90-99% chance the result is true. Other terms used to communicate confidence include “extremely likely” (greater than 95% chance the result is true); “likely” (greater than 66% chance the result is true) and “extremely unlikely” (less than 5%). The term “virtually certain” conveys that there is a greater than 99% chance that a result is true. These judgmental estimates originate from the Intergovernmental Panel on Climate Change (IPCC, 2007).

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