Has Increased Solar Activity Caused Recent Global Warming?

Check out this answer from Consensus:

While increased solar activity has some influence on global temperatures, the overwhelming evidence points to greenhouse gases as the primary driver of recent global warming. Solar activity contributes to climate variability, but its impact is relatively minor compared to the effects of anthropogenic greenhouse gas emissions.

The debate over the causes of recent global warming has been ongoing, with various factors being considered. One of the key questions is whether increased solar activity has contributed significantly to the observed rise in global temperatures. This article examines the role of solar activity in recent global warming by reviewing findings from multiple research studies.

The Role of Solar Activity

Solar activity, including variations in solar radiation and geomagnetic activity, has been proposed as a potential driver of climate change. Some studies suggest that changes in solar activity could influence global temperatures through mechanisms such as cloud formation and cosmic rays.

Solar Activity and Cloud Formation

One study associates recent climate warming with variations in solar-geomagnetic activity, which affect global cloud formation. The study suggests that the contribution of greenhouse gases to global warming is insignificant compared to the impact of solar activity on cloud cover2.

Solar Dimming and Brightening

Another study explores the impact of surface solar radiation variations on global warming. It finds that solar dimming masked the full extent of greenhouse warming until the 1980s, after which solar brightening revealed the full dimension of the greenhouse effect. This study concludes that recent solar brightening cannot supersede the greenhouse effect as the main cause of global warming3.

Greenhouse Gases vs. Solar Activity

While solar activity has some influence on global temperatures, the majority of studies emphasize the dominant role of greenhouse gases in recent global warming.

Greenhouse Gas Emissions

Research indicates that the increase in net radiation absorbed by the Earth is primarily due to the greenhouse effect from increasing greenhouse gases and water vapor, rather than changes in solar radiation. The main warming comes from increases in absorbed solar radiation due to decreasing cloud amounts, which is a feedback mechanism rather than a direct cause1.

Limited Impact of Solar Activity

Several studies have quantified the contribution of solar activity to global warming and found it to be relatively minor. For instance, one study estimates that the contribution of solar activity to global warming is less than 10% of the warming observed in the twentieth century5. Another study suggests that a potential future grand solar minimum would only compensate for a small fraction of the expected greenhouse warming4.

Regional and Temporal Variations

The impact of solar activity on climate can vary regionally and temporally. For example, a study on the regional climate impacts of a possible future grand solar minimum finds significant regional effects, particularly in northern high-latitude winters. However, the overall global impact remains small compared to anthropogenic warming7.

Has increased solar activity caused recent global warming?

Pablo Mauas has answered Extremely Unlikely

An expert from Institute of Astronomy and Space Physics in Astrophysics

This idea was mainly based on evidence that solar activity, as measured by the Sunspot Number, was increasing during the 20th century, reaching what some researchers called the Modern Grand Maximum. However, it was later found that this increase was due to an error in the calibration of the Group Sunspot Number [1]. As an official press release by the International Astronomical Union states, “it [is now] difficult to explain the observed changes in the climate that started in the 18th century and extended through the industrial revolution to the 20th century as being significantly influenced by natural solar trends.” [2]

Furthermore, [3] showed that “over the past 20 years, all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.” For example, the last complete Solar Cycle was the weakest since the 1970s: the Sunspot Number for the years 2008 and 2009 were the lowest since 1913, and the minimum between the last and the present Solar Cycles had the largest number of spotless days since the 1910s.

[1] L. Svalgaard, in Comparative Magnetic Minima: Characterizing Quiet Times in the Sun and Stars, International Astronomical Union Symposium, Vol. 286, pp. 27-33. (2012)

[2] https://www.iau.org/news/pressreleases/detail/iau1508 (2015)

[3] M. Lockwood and C. Fröhlich, Proc. Royal Society Astronomy 463, 2447 (2007)

Has increased solar activity caused recent global warming?

Gerald Meehl has answered Unlikely

An expert from National Center for Atmospheric Research in Earth Sciences, Climatology

Solar activity, as measured by the sunspot count and total solar irradiance measurements by satellites, has had a decreasing trend since the late 1970s (http://spot.colorado.edu/~koppg/TSI/) while globally averaged surface temperatures have had in increasing trend during that time period. Therefore, solar activity has not caused recent global warming.

Has increased solar activity caused recent global warming?

Michael Wehner has answered Extremely Unlikely

An expert from Lawrence Berkeley National Laboratory in Climatology

Formal protection and attribution studies are the gold standard for claiming an effect due to the human changes to the composition of the atmosphere. Such analyses of the effect of natural solar variations reveal that the “fingerprint” of these variations are incompatible with the observed changes in atmospheric temperature. Ignoring the fact that the effect of solar variations are too small to explain observed surface temperature increases, let’s focus on the pattern of warming aloft. That pattern is a warming of the troposphere and a cooling of the stratosphere. Increases in solar radiation fluxes causes warming of BOTH the troposphere and the stratosphere, contrary to what is well established by the satellite observational record. Only changes in greenhouse gases can explain this observed pattern of temperature change in the atmosphere.

Has increased solar activity caused recent global warming?

Damon Matthews has answered Extremely Unlikely

An expert from Concordia University in Climatology

Solar variations are an important driver of climate changes on long (100 to billion year) timescales. Variations in solar insolation over the past 200 years, however, have been quite small — something like 10 times smaller than the effect of increasing greenhouse gas concentrations. Furthermore, solar insolation has decreased slightly since about 1950, so cannot explain recent climate warming. Other indirect solar-climate influences (such as cloud responses to cosmic ray changes) have not been found to have a significant climate effect. So there is no evidence that solar activity changes have made any significant contribution to recent global warming.

Has increased solar activity caused recent global warming?

Joanna Haigh has answered Extremely Unlikely

An expert from Imperial College London in Atmospheric Science

Solar radiation output, averaged over 11-year activity cycles, increased slightly from 1900 to about 1970 but then flattened off, or started to decline – i.e. no correspondence with global temperatures. See here

The following figure, from the most recent assessment report of the Intergovernmental Panel on Climate Change, shows the radiative inbalances introduced into the climate by various natural and human factors. The Sun’s contribution is the little yellow wiggle at the top. Other factors, especially CO2, are far larger.

Aside from its output in irradiance other indications of solar activity include an influence on galactic cosmic rays. Suggestions that GCRs (which are anticorrelated with solar activity) create clouds and thus cool the planet are likewise not borne out by the evidence as, even if they did influence cloud (not proven), they have been rising overall recently (as irradiance declined).

There is some evidence that solar activity may influence regional climate (e.g. North Atlantic in winter) but this is insignificant to “global warming”.

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