How do we trace human’s impact on the climate?

Even without climate models, scientists can tell people play a big role in today’s warming climate by putting together many clues. These “human fingerprints” show indisputable facts: People are adding extra greenhouse gases are in the air and are causing unnatural warming.


NOAA traces greenhouse gases in the atmosphere to human fossil fuel emissions Carbon dioxide (CO2) in greenhouse gases created by burning fossil fuels is lighter than the CO2 emitted from natural sources.3 The carbon in fossil fuels, which is mostly ancient plant and animal matter, has a slightly different type of carbon than that emitted by plants. Scientists can tell the difference between naturally occurring CO2 emissions and those that are man-made.

NOAA scientists sampled and weighed the greenhouse gases from the air at 12 locations across the globe, comparing the carbon in the samples to carbon found in natural sources. They found the carbon in the air is getting lighter at the same time people increase fossil fuel use. This is strong evidence that the atmospheric changes over the past few decades stem from human emissions.(4),(5)

Greenhouse gases unevenly warm the atmosphere
Studies have found that greenhouse gases are accumulating in the air, causing the upper atmosphere to cool while the lower atmosphere warms. After the sun’s rays hit the earth, heat typically radiates back up and out to the upper and lower parts of the atmosphere. But NASA satellites have observed an excess of greenhouse gases – caused by human activities – trapping heat in the lower atmosphere. The extra gases causes the upper atmosphere to cool while the lower atmosphere warms.(1)


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Greenhouse gases trap outgoing heat and reduce Earth’s ability to cool off at night
Greenhouse gases warm the Earth by trapping heat coming off the surface. The additional greenhouse gases in the atmosphere act as a blanket, reducing the cooling at night and the difference in temperature between days and nights. Satellite observations across the globe find the difference in temperature between nights and days is getting smaller – another fingerprint showing human emissions of greenhouse gases cause climate change.(2)


More evidence humans are responsible for climate change

  • Greenhouse gases trap specific types of heat. Satellites detect an increase in these types in the atmosphere.(6)
  • Greenhouse gases trap heat in the lower atmosphere, causing the lower atmosphere to warm while the upper atmosphere cools.(1)
  • Because warm air rises, these changes in temperature cause the boundary between the lower atmosphere and the upper atmosphere to get higher. NASA satellites observe the boundary is indeed rising.(7),(8)



  1. American Geophysical Union: Revisiting the Determination of Climate Sensitivity from Relationships between Surface Temperature and Radiative Fluxes
  2. American Geophysical Union: Global Observed Changes in Daily Climate Extremes of Temperature and Precipitation
  3. Intergovernmental Panel on Climate Change
  4. NOAA: Stable Carbon and the Carbon Cycle
  5. NOAA: What Carbon-14 Tells Us
  6. NOAA: Measurements of the Radiative Surface Forcing of Climate
  7. University Corporation for Atmospheric Research
  8. Science
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