The Sun cannot explain recent global warming, contrary to what Heartland Institute report claims

Key takeaway

The warming influence of CO₂ has been much greater than that of the Sun over the past century, and the pattern of observed climate change cannot be explained by solar forcing.

Reviewed content

Verdict:

Incorrect

Claim:

Solar forcings are not too small to explain twentieth century warming. In fact, their effect could be equal to or greater than the effect of CO₂ in the atmosphere.

Verdict detail

Incorrect: The fingerprints of the observed climatic changes do not match those that a change in solar irradiance would generate.
Factually Inaccurate: No estimate of 20th century climate forcings (warming or cooling influences) shows the solar forcing to be close to the effect of increased CO₂.

See our method of evaluation

Full Claim

Solar forcings are not too small to explain twentieth century warming. In fact, their effect could be equal to or greater than the effect of CO₂ in the atmosphere.

Timothy Osborn

Professor, University of East Anglia, and Director of Research, Climatic Research Unit

There is strong evidence that solar forcing cannot explain much of the observed warming at all. The “fingerprint” of solar forcing does not match the observed changes at all, neither over time nor space. Solar forcing would warm both the stratosphere and the surface of the Earth, whereas CO₂ warms the surface (and the troposphere) but cools the stratosphere. Using radiosondes and (more recently) satellites, we have observed a warming surface and troposphere together with a cooling stratosphere. See Santer et al (2013)* for one of many studies providing this evidence.

Figure – Zonal-mean atmospheric temperature trends in satellite observations from January 1979 to December 2012 showing warming of the lower atmosphere (troposphere) and cooling of the upper-atmosphere (stratosphere), from Santer et al (2013)*

• Santer et al (2013) Human and natural influences on the changing thermal structure of the atmosphere, PNAS

Britta Voss

Postdoctoral Research fellow, U.S. Geological Survey

Solar forcing is much smaller than CO₂ forcing. As this figure from the latest IPCC report shows, CO₂ radiative forcing (1.68 W/m²) dwarfs solar forcing (0.05 W/m²). Along with other greenhouse gases, CO₂ dominates the total radiative forcing when all positive and negative factors are taken into account.

Figure – Radiative forcing estimates in 2011 relative to 1750. Values are global average radiative forcing, partitioned according to the emitted compounds or processes that result in a combination of drivers. Source IPCC AR5

Peter deMenocal

Professor, Lamont-Doherty Earth Observatory, Columbia University, and Director, Center for Climate and Life

This is untrue. Solar forcing in the visible spectrum is far too small to explain recent warming. Furthermore solar variability would suggest a cooling trend more recently whereas the Earth is clearly warmed.