“Fingerprint” of humanity’s climate impact seen in the seasons

Enlarge / Trends in the satellite-measured seasonal temperature cycle of the troposphere (red means larger temperature swing, blue means smaller temperature swing). (credit: Santer et al./Science)

One reason climate scientists have been able to confidently determine that humans are responsible for modern warming is that they have more than just weather records to work with. There are many places where a human cause can be identified if you know how to dust for fingerprints. For example, while the lower atmosphere warms, the stratosphere is actually cooling. That’s what you expect when greenhouse gases—rather than the Sun—are behind the warming.

A new study led by Lawrence Livermore National Laboratory’s Ben Santer looked for fingerprints in a new place: the seasonal cycle of temperatures. The ideal tool for analyzing this is the global temperature record produced by satellites, which began their watch in 1979. That means they don’t go back nearly as far as weather-station records, but the dataset is now long enough to be useful for studies like this.

Hot and cold

While everyone uses the same satellites, several different groups actually maintain separate satellite temperature datasets. This is because the measurements are far from straightforward, and a ton of work goes into all the necessary processing to spit out temperature maps. As a result, the different datasets don’t always line up perfectly with each other—or with those analyzed with previous versions of their processing algorithm. So in this study, the researchers used the most recent two versions of three different datasets.

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“Fingerprint” of humanity’s climate impact seen in the seasons