Although some people continue to question whether Earth's temperatures have actually warmed significantly over the last century, the focus of many has shifted to cause: while the world has clearly warmed, a lot of people have suggested that the cause of that warming is "up for debate." Many studies have looked at that question and determined that human activity is the primary driver, as the 2007 IPCC report concluded. A paper published this week in Nature Geoscience makes a novel contribution to this question, even as it comes up with the same answer.

Previous work has primarily used observations of temperature trends (from the deep ocean or the lower atmosphere) combined with computer modeling to assess the cause of warming. For example, the latest IPCC report showed climate models run with and without the effect of greenhouse gases to illustrate that temperatures would have been stable without anthropogenic warming.

The new study, published by researchers from the Institute for Atmospheric and Climate Science at ETH in Switzerland, directly examined Earth’s energy balance instead.

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