General questions

• Is the ozone hole causing climate change?

  Yes and no. The ozone hole is not causing global warming, but it is affecting atmospheric circulation.

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• What’s the difference between climate change and global warming?

  “Global warming” refers to the long-term warming of the planet. “Climate change” encompasses global warming, but refers to the broader range of changes that are happening to our planet, including rising sea levels; shrinking mountain glaciers; accelerating ice melt in Greenland, Antarctica and the Arctic; and shifts in flower/plant blooming times.

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• Do scientists agree on climate change?

  Yes, the vast majority of actively publishing climate scientists – 97 percent – agree that humans are causing global warming and climate change.

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• What’s NASA got to do with climate change?

  NASA’s role is to make observations of our Earth system that can be used by the public, policymakers and to support strategic decisions. Its job is to do rigorous science. However, the agency does not promote particular climate policies.

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• What is the greenhouse effect?

  The greenhouse effect is the way in which heat is trapped close to the surface of the Earth by “greenhouse gases.”

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• How do we know what greenhouse gas and temperature levels were in the distant past?

  Ice cores are scientists’ best source for historical climate data. Other tools for learning about Earth’s ancient atmosphere include growth rings in trees, which keep a rough record of each growing season’s temperature, moisture and cloudiness going back about 2,000 years. Corals also form growth rings that provide information about temperature and nutrients in the tropical ocean. Other proxies, such as benthic cores, extend our knowledge of past climate back about a billion years into the past.

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• Why does the temperature record shown on your "Vital Signs" page begin at 1880?

  Three of the world’s most complete temperature tracking records – from NASA’s Goddard Institute for Space Studies, the National Oceanic and Atmospheric Administration’s National Climactic Data Center and the UK Meteorological Office’s Hadley Centre – begin in 1880. Prior to 1880, temperature measurements were made with instruments like thermometers. The oldest continuous temperature record is the Central England Temperature Data Series, which began in 1659, and the Hadley Centre has some measurements beginning in 1850, but there are too few data before 1880 for scientists to estimate average temperatures for the entire planet.

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• Is the Sun causing global warming?

  No. The Sun can influence Earth’s climate, but it isn’t responsible for the warming trend we’ve seen over the past few decades.

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• What’s the difference between weather and climate?

  “Weather” refers to the more local changes in the climate we see around us, on short timescales from minutes to hours to days to weeks. Examples are familiar – rain, snow, clouds, winds, thunderstorms, heat waves and floods. “Climate” refers to longer-term averages (they may be regional or global), and can be thought of as the weather averaged over several seasons, years or decades.

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• Is it too late to prevent climate change?

  Humans have caused major climate changes to happen already, and we have set in motion more changes still. Even if we stopped emitting greenhouse gases today, global warming would continue to happen for at least several more decades, if not centuries.

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• May I use content and imagery from your website? If so, to whom do I credit them?

  Unless otherwise noted, you may use our content and imagery without permission, as long as you provide due credit.

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• What do volcanoes have to do with climate change?

  Overall, volcanoes release less than 2 percent of the equivalent amount of CO₂ released by human activities. Quite small.

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• Can you explain the urban heat island effect?

  While urban areas are warmer than surrounding rural areas, the urban heat island effect has had little to no effect on our warming world, because scientists have accounted for it in their measurements.

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• What happens if the next solar cycle becomes less active? Will we go into a new ice age?

  No. Even if the amount of radiation coming from the Sun were to decrease as it has before, it would not significantly affect the global warming coming from long-lived, human-emitted greenhouse gases. Further, given our greenhouse gas emissions to date and those expected to come, the evidence points to the next “ice age” being averted altogether.

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• Has Earth continued to warm since 1998?

  Yes, evidence shows warming from 1998 to the present, with the four most recent years (2014, 2015, 2016 and 2017) being the four warmest years globally since 1880.

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• Are the land-based ice sheets in Greenland and Antarctica continuing to lose mass (ice)?

  Data from NASA's GRACE satellites, which measured Earth’s gravity field, show that the land ice sheets in both Antarctica and Greenland have been losing mass (ice) since 2002. Both ice sheets have seen an acceleration of ice mass loss since 2009.

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• Which measurement is more accurate: taking Earth’s surface temperature from the ground or from space?

  Since satellites technically measure neither temperature nor the surface (where people live), it’s safe to say that ground thermometers are more accurate than satellite measurements.

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• How are Earth’s mountain glaciers faring in a warming world?

  On average, most of Earth’s mountain glaciers are continuing to melt.

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• How is Earth’s sea ice faring in our warming world?

  Arctic sea ice volume and extent have been declining since record-keeping began in the late 1970s and prior. Antarctic sea ice extent is currently below the long-term average of prior decades since 1979.

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• Is the ocean continuing to warm?

  ​Yes, the ocean is continuing to warm. Notably, all ocean basins have been experiencing significant warming since 1998, with more heat being transferred deeper into the ocean since 1990.

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Less frequently asked, but interesting

• Which is a bigger methane source: cow belching or cow flatulence?

  Contrary to common belief, it’s cow belching due to enteric fermentation.

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• If all of Earth's ice melts and flows into the ocean, what would happen to the planet's rotation?

  Melting land ice, like mountain glaciers and the Greenland and Antarctic ice sheets, will change the Earth’s rotation only if the meltwater flows into the oceans. For example, if the Greenland ice sheet were to completely melt and the meltwater were to completely flow into the oceans, then global sea level would rise by about seven meters (23 feet) and the Earth would rotate more slowly, with the length of the day becoming longer than it is today, by about two milliseconds.

  Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice displaces its volume and, hence, does not change the Earth’s rotation.

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• How do I cite your website?

  It depends on the style you’re using. Read on for a few examples.

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How global temperatures are studied

• Can scientists use the data as is?

  No. To understand why not, imagine you're a nurse checking a patient's chart. You find the following temperature readings (Fahrenheit) for the last few hours: 99.2, 99.8, 1000, 101.4. You'd know immediately that the third number was a mistake. To make a realistic assessment of the patient's condition, you'd have to either adjust it or throw it out.

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• Once the mistakes are eliminated, are the data ready to use?

  Not yet. They have to be adjusted to account for all the changes that happen over time. Read on to learn more about those changes.

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• What kinds of data do scientists use to study climate?

  Climate researchers use every possible direct and indirect measurement to study the full history of Earth's climate, from the latest satellite observations to samples of prehistoric ice extracted from glaciers.

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• How do scientists know their data-processing techniques are reliable?

  The records of global temperatures calculated by U.S. and other major climate research organizations are remarkably similar, despite the different data-processing techniques used. The techniques used by NASA's Goddard Institute for Space Studies (GISS), National Climatic Data Center (NCDC) and other respected groups are peer reviewed, and the processed data sets have undergone many peer-reviewed analyses as well.

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• Where do the data come from?

  Modern observations mostly come from weather stations, weather balloons, radars, ships and buoys, and satellites.

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• How do scientists deal with these changes?

  Major climate research organizations worldwide have developed mathematically rigorous, peer-reviewed data processing methods to identify and compensate for changes in observing conditions.

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• Does data processing destroy the original data?

  No, the original records are preserved and are available at no cost online. You can access the National Climatic Data Center's (NCDC) U.S. and global records here.

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• Does data processing make temperature data warmer?

  Almost half of the National Oceanic and Atmospheric Administration's (NOAA) corrected data are cooler than the original records. NOAA's corrections of temperatures over the oceans — done to compensate for changes in methods of observing the temperature of water at the surface of the ocean — reduced the warming trend in global temperature.

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