How does global warming work?

Earth’s temperature is about 60 degrees Fahrenheit. Temperatures in space are frigid, well below freezing. So why doesn’t Earth’s warmth leak into space?

The planetary blanket
Certain gases, known as greenhouse gases, trap heat like a blanket. They’re so effective, the Earth would be about 0 degrees Fahrenheit without them.(1) This effect is undisputed by scientists. The planet’s “blanket” of greenhouse gases, including carbon dioxide and methane, has been widely studied and known by scientists for over 150 years.(2),(3),(4)

What has most scientists concerned is that the blanket is getting thicker: greenhouse gases in the air are steadily building up. And these “extra” gases can be traced back to human sources such as burned gasoline and coal. This process of unnatural warming is often referred to as “global warming” or “climate change”.

How do greenhouse gases work?
When sunlight hits the Earth’s surface, it turns into heat and bounces back toward space. Without greenhouse gases, the heat would escape and the Earth’s temperature would be below freezing. Greenhouse gases act as a blanket and warm the Earth by absorbing the heat that would otherwise be sent to space. This process is what’s known as the greenhouse effect.(5),(6),(7),(8)

the-blanket

A human influence
Most greenhouse gases have natural sources, but human activities are causing more to accumulate in the atmosphere.(9) Emissions from people exceed what nature can absorb and warm the planet beyond natural variability.(10),(11)

“The facts of the matter are this: the planet’s climate has changed over the last 30 years, chiefly because of human activities.”
– Dr. Gavin Schmidt, Director of NASA’s Goddard Institute for Space Studies, 2011

Greenhouse gases vs. other gases in the low atmosphere
Long-lasting greenhouse gases, such as carbon dioxide and methane, are just 0.1 percent of the total atmosphere. Despite their low numbers, the Earth is about 60 degrees warmer because of them.1 Scientists project that future increases can have big impacts on our climate and temperatures. MIT climate models suggest that the world’s average temperature will increase about 10 degrees Fahrenheit (5.2 degrees Celsius) by the end of the century, if emissions over the coming years remain unmanaged.(12)

atmospheric-composition

Types of Greenhouse Gases
Carbon dioxide is the most common greenhouse gas, but many others exist such as water vapor, methane, and nitrous oxide. Greenhouse gases are not all the same. Their heat-trapping ability depends on two main things. First, how long it stays in the air before it is reabsorbed by nature. And second, how well it prevents heat from escaping into space– much like how some blankets are thicker than others.(13)

warmer-from-ghgs

Carbon Dioxide (CO2)
Carbon dioxide is arguably the most important greenhouse gas because it is 200 times more abundant in the atmosphere than methane, the next most common greenhouse gas.(14) It is also long-lived. One CO2 molecule released into the air today will warm the Earth for about 100 years. CO2 is a byproduct of many activities such as electricity generation and car-driving.(15) Carbon dioxide’s ebbs and flows have also been linked to major climatic changes in the past.(16),(17)

Methane (CH4)
Methane is a very potent greenhouse gas, about 25 times stronger than carbon dioxide.(18 The reason why it is less of an issue than carbon dioxide is simply because much less of it is being produced.(19 It is released by human sources such as cattle farms, natural gas wells and landfills.(20)

Nitrous oxide (N2O)
N2O is one of the strongest greenhouse gases, with predominantly human sources. Although it lasts nearly as long in the atmosphere as CO2, it is about 300 times more potent.(21) Common sources include factories, agriculture and cars.(22)

Synthetic
Most of the remaining greenhouse gases do not have natural sources. For example, some synthetic gases used in semiconductor manufacturing are more than 6,500 times stronger than CO2 and can remain in the atmosphere as long as 50,000 years.(23),(24)

Water vapor
Water vapor is the most abundant greenhouse gas in the atmosphere.(25) While it is the most common greenhouse gas, water vapor does not cause long-term changes because it only survives in the atmosphere for a few days. Rather, it amplifies long-term warming or cooling cycles.(26)

 

 

SOURCES

  1. NASA: Global Warming
  2. World Meteorological Organization: Understanding Climate
  3. American Chemical Society: What Is the Greenhouse Effect?
  4. National Geographic: Greenhouse Effect
  5. NOAA: Introduction
  6. Royal Society: Basics of Climate Change
  7. National Academy of Sciences: Climate Change Evidence and Causes
  8. American Meteorological Society: Climate Change
  9. NOAA: Carbon Cycle Science
  10. NASA: The Carbon Cycle
  11. NASA: Causes
  12. Massachusetts Institute of Technology: MIT News
  13. Environment Canada
  14. Oak Ridge National Laboratory: Recent Greenhouse Gas Concentrations
  15. Energy Information Agency: Carbon Dioxide Emissions
  16. NASA: Carbon Dioxide Controls the Earth’s Temperature
  17. NOAA: Temperature Change and Carbon Dioxide Change
  18. NOAA: Carbon Dioxide, Methane Rise Sharply in 2007
  19. Scientific American: The Worst Climate Pollution is Carbon Dioxide
  20. Energy Information Agency: Methane Emissions
  21. Intergovernmental Panel on Climate Change: Global Warming Potential
  22. Energy Information Agency: Nitrous Oxide Emissions
  23. Institute of Electrical and Electronics Engineers
  24. Intergovernmental Panel on Climate Change: Global Warming Potential
  25. NOAA: Water Vapor
  26. University of California, San Diego: The Importance of Water

 

GRAPHIC UPDATES

  1. Atmospheric Composition – NCSU
  2. Warming from long-lived greenhouse gases – NOAA
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