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Science
This page provides EPA’s answers to frequently asked questions about the science of climate change. Click on a question below to view the answer. Links throughout the answers will guide you to further information on EPA’s Climate Change site or from other sources.
- What is the difference between climate and weather?
- What is the difference between climate change and global warming?
- Does ozone layer depletion have anything to do with climate change?
- Does El Niño have anything to do with climate change?
- What is the greenhouse effect?
- How have greenhouse gas levels in our atmosphere changed since the Industrial Revolution?
- When was climate change discovered?
- How has the Earth’s climate changed in the past?
- When will the climate change?
- Are human activities responsible for the warming climate?
- Can changes in climate be attributed to natural factors?
- How do scientists predict future climate?
- How much is the climate expected to warm?
- Will the climate change uniformly across the globe?
- What is the Intergovernmental Panel on Climate Change (IPCC)?
- What is the difference between climate and weather?
Because climate can be thought of as average weather, the two are closely related. However, climate and weather are different. The main distinction between the two is the timeframe. Weather describes short-term atmospheric conditions in a specific place, such as a sunny day in Los Angeles or a snowstorm in Boston. Climate, on the other hand, refers to average atmospheric conditions over an extended period of time, such as decades or centuries. Using the cities of Los Angeles and Boston as examples again, these two locations have very different climates, even though their weather can possibly be similar on any one day.
Source: IPCC “AR4 WG1 FAQs” 2007 (PDF)
(128 pp, 10.9MB, About PDF)
- What is the difference between climate change and global warming?
The term climate change is often used interchangeably with the term global warming, but according to the National Academy of Sciences, "the phrase 'climate change' is growing in preferred use to 'global warming' because it helps convey that there are [other] changes in addition to rising temperatures." 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). Global warming is an average increase in the temperature of the atmosphere near the Earth's surface and in the troposphere, which can contribute to changes in global climate patterns. Global warming and climate change can be caused by a variety of factors, both natural and human-induced.
Source: EPA Climate Change Basic Information - Does ozone layer depletion have anything to do with climate change?
Climate change and ozone depletion are two distinct but interrelated issues. Ozone depletion is not a principal cause of climate change and climate change is not a principal cause of ozone depletion. However, ozone-depleting gases -- such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons -- are greenhouse gases that do contribute to climate change. Ozone itself is a greenhouse gas and has an effect on climate. In addition, certain changes in Earth’s climate could affect the future condition of the ozone layer. For example, low temperatures and strong polar winds both affect the extent and severity of winter polar ozone depletion.
Source: EPA Ozone: 20 Questions and Answers (PDF) (39 pp, 2.1MB, About PDF)
Source: “EPA Ozone Science” - Does El Niño have anything to do with climate change?
El Niño is the strong warming of the equatorial Pacific Ocean that occurs about every two to seven years. Recent El Niño events have been very strong and have contributed to record-setting temperatures-evidence that El Niño events can warm parts of the Earth. Scientists are now examining how human-induced climate change could affect El Niño.
Source: IPCC Climate Change 2007: Technical summary (PDF) (74 pp, 14.8MB, About PDF) - What is the greenhouse effect?
The greenhouse effect is a natural phenomenon that helps regulate the Earth’s temperature. Greenhouse gases (e.g., carbon dioxide, methane, nitrous oxide, chlorofluorocarbons) act like an insulating blanket, trapping solar energy that would otherwise escape into space. 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. However, human activities, primarily the burning of fossil fuels and clearing of forests, have enhanced the natural greenhouse effect, causing the Earth’s average temperature to rise.
Source: IPCC “AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: EPA Climate Change Basic Information - How have greenhouse gas levels in our atmosphere changed since the Industrial Revolution?
Since pre-industrial times, atmospheric concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have climbed by over 36 percent, 148 percent, and 18 percent, respectively (see the Recent Atmospheric Change page on EPA’s Climate Change site for more details). Greenhouse gas concentrations in the atmosphere have varied historically as a result of many natural processes (e.g., volcanic activity, changes in temperature, etc). However, since the Industrial Revolution, humans have added a significant amount of greenhouse gases to the atmosphere primarily by burning fossil fuels, cutting down forests, and other activities. Scientists have confirmed that the recent increase in atmospheric greenhouse gas concentrations is primarily due to human activity.
Source: IPCC Climate Change 2007: Technical Summary (PDF) (74 pp, 14.8MB, About PDF)
Source: “EPA Future Atmospheric Concentration page” - When was climate change discovered?
The greenhouse effect was first described in theoretical terms by a Swedish researcher, Svante Arrhenius, in the late 1800s. However it wasn’t until the following century that Arrhenius’s theory was observed. In the 1930s, scientists realized that parts of the globe had warmed during the previous half-century. Then in the early 1960s scientists discovered that the level of carbon dioxide in the atmosphere was rising. Researchers began to take an interest and found a strong relationship between the increasing levels of carbon dioxide and average global temperature.
Source: Spencer Weart, “History of Climate Change Science,” The Discovery of Global Warming, June 2006. - How has the Earth’s climate changed in the past?
Climate has changed throughout the Earth’s history. Scientists have been able to piece together a picture of the Earth's climate dating back to millions of years ago by analyzing a number of measures of climate from ice cores, boreholes, tree rings, glaciers, pollen residues, and ocean sediments, and by studying changes in the Earth's orbit around the Sun. From these analyses, it is clear that the Earth has undergone intervals of both warming and cooling. The current warming trend is of particular significance because most of it is very likely human-induced and is likely proceeding at a rate that is unprecedented in the past 1,300 years. For more information, please visit the Past Climate page on EPA’s Climate Change site.
Source: IPCC “AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: “EPA Past Climate Change page” - When will the climate change?
The Earth has already warmed 1.3°F over the past century, and it is projected by the Intergovernmental Panel on Climate Change to increase by an additional 3.2-7.2°F over the 21st century. These increases may appear minor compared with short-term local temperature changes, such as those from night to day or winter to summer, but they are changes in the Earth’s global average temperature. To put this in perspective, global temperatures during the last ice age (about 20,000 years ago) were “only” 9°F cooler than today; however, that was enough to allow massive ice sheets to reach as far south as the Great Lakes and New York City. At the high-end of projected warming, human activities would change Earth’s climate by up to 7°F but in the opposite direction. For more information, visit the Recent Climate Change and Future Climate Change pages on EPA’s Climate Change site.
Source: IPCC “AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: “EPA Global Warming FAQs”. April, 2000
Source: “EPA Future Atmospheric Concentration page” - Are human activities responsible for the warming climate?
Careful measurements have confirmed that greenhouse gas emissions are increasing and that human activities (principally, the burning of fossil fuels and changes in land use) are the primary cause. Human activities have caused the atmospheric concentrations of carbon dioxide and methane to be higher today than at any point during the last 650,000 years. Scientists agree it is very likely that most of the global average warming since the mid-20th century is due to human-induced increases in greenhouse gases, rather than to natural causes.
Source: IPCC “AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: IPCC Climate Change 2007: WGI Summary for Policy Makers (PDF) (18 pp, 2.9MB, About PDF) - Can changes in climate be attributed to natural factors?
Natural variations within the Earth’s climate system can cause small changes over decades to centuries. Larger changes can occur through factors such as gradual changes in Earth’s orbit around the Sun, which are thought to be the key contributors in the comings and goings of past ice ages over many millennia. The Sun’s energy can also vary over time. Large volcanic eruptions and collisions with large meteorites can cool the planet for a few years by spewing out particles that reflect sunlight back out to space. However, while natural variations have altered the climate significantly in the past, it is very unlikely that the changes in climate observed since the mid-20th century can be explained by natural processes alone.
Source: IPCC "AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: IPCC Climate Change 2007: Technical summary (PDF) (74 pp, 14.8MB, About PDF) - How do scientists predict future climate?
Future climate change is predicted principally through the use of climate models. These models are mathematical representations of the climate system, expressed as computer simulations. While scientists are more confident in model estimates for some climate variables (e.g., temperature) than for others (e.g., precipitation), there is significant confidence that climate models provide credible estimates of future climate change. This assurance stems from the fact that climate models are based on accepted physical principles as well as their ability to reproduce observed features of current climate and past climate changes. Still, predicting any event in the future is an uncertain business, and estimates of future climate change are given as projections with a range of uncertainty. The degree of uncertainty is higher for regional and local projections than it is for continents and the Earth as a whole. Models are improving in their ability to simulate regional climates, but scientists are less confident in their predictions at small scales. For more information, visit the State of Knowledge page on EPA’s Climate Change site.
Source: IPCC "AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
- How much is the climate expected to warm?
Scientists project an average global temperature increase of 3.2-7.2°F by 2100, and greater warming thereafter. Because human emissions of carbon dioxide and other greenhouse gases continue to climb, and because they remain in the atmosphere for decades to centuries (depending on the gas), we’re committing ourselves to a warmer climate in the future. In addition, temperatures will not change uniformly across the globe. In some parts of the globe (e.g., the polar regions) temperatures are expected to rise even faster than the global average, while other regions may warm more slowly than average. For more information, visit the Future Climate Change page on EPA’s Climate Change site.
Source: “EPA Future Atmospheric Concentrations page” - Will the climate change uniformly across the globe?
Climate change will not occur equally across our planet, nor will its impacts be felt equally everywhere. Climate is driven by the interactions among solar heating and the atmosphere, oceans, and land surfaces. Variation in solar and geographic factors will cause regional climates to change at different rates and magnitudes. Further, not all ecosystems and human settlements are equally sensitive to changes in climate. Nations (and regions within nations) vary in their relative vulnerability to changes in temperature, precipitation, and extreme weather events, and in their ability to cope with such changes. For more information, visit the International Impacts page of EPA’s Climate Change site.
Source: IPCC "AR4 WG1 FAQs” 2007 (PDF) (128 pp, 10.9MB, About PDF)
Source: IPCC Climate Change 2007: Technical summary (PDF) (74 pp, 14.8MB, About PDF)
Source: “EPA International Impacts page” - What is the Intergovernmental Panel on Climate Change (IPCC)?
The IPCC was formed jointly in 1988 by the United Nations Environment Program and the World Meteorological Organization. The IPCC brings together the world’s top scientists in all relevant fields, synthesizes peer-reviewed scientific literature on climate change, and produces authoritative assessments of the current state of knowledge of climate change. It produces periodic reports on scientific, technical, and socio-economic information relevant for the understanding of climate change, its potential impacts, and options for adaptation and mitigation. The most recent report series
Source: IPCC was released in 2007.
