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CSI: Climate Science Investigation

nssl.noaa.gov
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The Earth has gone through huge climatic changes throughout its history, with multiple ice ages broken up by warmer periods. We’re currently in a warming trend, and that trend follows an increase in carbon dioxide, a common greenhouse gas produced by burning fossil fuels. Is this cause-and-effect, or coincidence?

“What’s the role of people, of our burning fossil fuels and adding CO2 and other greenhouse gases to the atmosphere, and that’s a great question," said Bruce Hungate, a professor of ecosystem science at Northern Arizona University. "That’s a good question. That’s a question scientists have taken very seriously over the last few decades.”

Hungate studies the causes of climate change, and like a forensic scientist investigating a crime, he looks for clues. Some skeptics argue that the sun is in a natural warming cycle, and that people are not contributing to global warming. This can be tested.

The atmosphere is made up of layers, and the troposphere is the closest to the Earth. That’s where all the weather happens, and where greenhouses gases build up. The stratosphere is the next layer up, and doesn’t accumulate greenhouse gases. Sunlight is hitting all the layers, so they should all heat up equally if that is the cause of climate change. If greenhouse gases are to blame, they should heat up differently. Weather balloons with sensors and satellites are used to measure the temperature of the different layers.

“And the data are overwhelming in that they show exactly as the idea of human-caused global warming predicts," Hungate said. "They show that the troposphere is warming, and the stratosphere is cooling. That’s an example of a fingerprint.”