Is it true that climate change is being caused by natural variations in the sun’s output, not human activity?

This is a common question that climate scientists get asked. The sun provides the primary source of energy driving Earth’s climate system, and changes in the sun’s energy output have played a role in past climate changes.

However, as shown in Figure 1 (below), direct satellite measurements of the Sun’s energy reaching Earth since the late 1970s show no net increase in the Sun’s output, while at the same time global surface temperatures have increased.

Furthermore, most up-to-date climate models – including those used by the IPCC and researchers at Cornell University – include the effects of the sun’s variable brightness in their calculations. These climate models can’t reproduce the observed temperature trends over the past century or more without including a rise in human emitted greenhouse gases.

Graph showing temperature vs. solar activity


Figure 1: Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Krivova et al 2007 (data). TSI from 1979 to 2009 from PMOD (see the PMOD index page for data updates).

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Category: Climate Change Q&A

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