Rising Global Temperatures

What We Know

"Global temperatures are going up." The scientific consensus around this alarming fact is overwhelming. Global temperatures have risen about 2.1ºF (1.2ºC) since 1880 (when the Industrial Revolution kicked off and humans started releasing greenhouse gases), which can be directly attributed to human activities. This amount may not seem like much when considering daily temperatures, but consider this fact with the entire world being 2.1ºF hotter. To put this number in perspective, scientists estimate that the most recent Ice Age only had temperatures about 9ºF cooler than current (pre-industrial) average temperatures. Small temperature changes make an enormous difference.

The interactive graph below (with data from NASA) shows how temperatures have changed based on the 1950–1980 average. As you can see, there has been a shocking increase in global temperatures, particularly in the last forty years.

We also know that greenhouse gases are the cause of this warming. There is a natural greenhouse cycle to keep the earth heated and able to sustain life. However, humans are creating a variation in the natural cycle.

Temperature Anomaly Based on 1950-1980 Average

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How We Know

There are two parts to this question: how scientists know the earth is warming and how they attribute it to humans. First, scientists know the earth is warming through careful measurements since 1880 at thousands of locations across the world. In modern times, readings are incredibly accurate because scientists use stations across the world and satellite technology while employing complex methods to eliminate errors (such as different instruments taking different measurements) from the results. In particular, satellite technology allows scientists to measure air temperature and surface temperature and compare results to ensure accurate readings.

Even before humans started emitting greenhouse gases, scientists discovered how they can absorb heat. Their heat-absorbing properties were first discovered in the 1820s when scientists conducted tests on these gases using just basic physics. In 1956, James Rodger Fleming's article in American Scientist reaffirmed that carbon dioxide has a "greenhouse effect" on the earth. (Click here to read more about the greenhouse effect and how scientists have determined climate change works.)

The IPCC (the leading international body on climate change) and other scientific groups use climate modeling to analyze what drives climate change. In 2013, the IPCC concluded that humans are the “dominant cause of the observed warming.” In particular, “fingerprint” models analyze each specific change within climate change (each fingerprint of climate change) to see what caused it. These models are a key part of proving that climate change is caused by humans.