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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Climate Hustle

Do solar cycles cause global warming?

What the science says...

A full reading of Tung 2008 finds a distinct 11 year solar signal in the global temperature record. However, this 11 year cycle is superimposed over the long term global warming trend. In fact, the authors go on to estimate climate sensitivity from their findings, calculate a value between 2.3 to 4.1°C. This confirms the IPCC estimate of climate sensitivity.

Climate Myth...

Solar cycles cause global warming
A new peer-reviewed study on Surface Warming and the Solar Cycle found that times of high solar activity are on average 0.2°C warmer than times of low solar activity, and that there is a polar amplification of the warming. This result is the first to document a statistically significant globally coherent temperature response to the solar cycle, the authors note (source: Mark Morano).

The study is Surface warming by the solar cycle as revealed by the composite mean difference projection by Charles D. Camp and Ka Kit Tung. They find a global warming signal of 0.18°C attributable to the 11-year solar cycle. Eg - from solar minimum to solar maximum, global temperatures increase 0.18°C due to an increase in Total Solar Irradiance (TSI). To find the solar signal, they detrended the temperature data by removing the global warming trend. They found the detrended temperature correlated well with the solar cycle.

TSI including 11 year solar cycle vs detrended surface temperature
Figure 1: Detrended temperature (solid) compared to TSI (dotted) (Camp 2007)

However, a fair degree of climate variability contaminated the signal. Volcanic eruptions in 1982 and 1991 coincided with solar maximums. Similarly, the El Nino peak of 1998 occured during low solar activity. Tung and Camp filtered out the noise using various statistical techniques and found an even higher correlation with the solar cycle.

They concluded that from solar minimum to maximum (eg - from 1996 to 2001), the forcing from the sun increases global temperatures by 0.18°C. Conversely, from solar maximum to minimum (eg - from 2001 to 2007), the reduced forcing from the sun cools global temperatures by 0.18°C. This 11 year cycle is superimposed over the long term global warming trend.

Climate Sensitivity

Camp and Tung explore the ramifications further in a follow-up paper Solar-Cycle Warming at the Earth’s Surface and an Observational Determination of Climate Sensitivity. Independently of models, they calculate a climate sensitivity between 2.3 to 4.1°C. Eg - if CO2 levels are doubled, global temperatures will increase around 3.2°C. This confirms the IPCC estimate of climate sensitivity. In Tung's own words, "The finding adds to the evidence that mainstream climate models are right about the likely extent of future human-generated warming. It also effectively rules out some lower estimates in those models."

The other significant finding is that solar forcing will add another 0.18°C warming on top of greenhouse warming between 2007 (we're currently at solar minimum) to the solar maximum around 2012. In other words, solar forcing will double the amount of global warming over the next five to six years.

Last updated on 9 July 2010 by John Cook.

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Comments 51 to 55 out of 55:

  1. CBDunkerson, thanks for the explanation and the link, this clarifies for me the issue with the WT (and, I finally know what "BEST" stands for...). But, their statement on solar radiation seems not to be backed up by their data. I am just starting reading about TSI, so I am very careful to accept figures and conclusions just as a given, yet.

    Lanfear, the figure 14 is wrong to use I believe, because it is just about faculae. Figure 15 presents three TSI curves from different studies, ranging from an increase between 1 and 2,5 W/m2. The study itself seems to come to a (eyeballed) result of 1 W/m2. I don't know if the 2,5W/m2 can be really called as outdated.
    As to the physical mechanism, I agree. But maybe the way of calculation of global temperature leaves room for some kind of heat storage (ice-melting, oceans, air streams, etc.) which is not captured by available data. I am not so sure we can confidently say "there is no physical mechanism".

    Tom Dayton, thanks for the link, this comes very close to what I was thinking about. But I don't get two things there:
    First, the TSI increase is said to be only "between 0.17 W/m2 (Wang 2005) to 0.23 W/m2 (Krivova 2007) since the Maunder Minimum". Wang 2005 is the same essay I quoted above, where I found this figure 15, where you can also eyeball 1 W/m2 to 2,5 W/m2 from different studies.
    Second, it is said that "Hansen 2005 estimates the climate lag time is between 25 to 50 years", and then "climate reached radiative equilibrium around the late 80's (give or take a decade)". If I count from 1960 onwards and assume 50 years, there could be a lagged warming until 2010 (which is exactly my point) and not the 80's.
    I probably will continue discussion over there, I still did not get all points. This whole TSI measuring and relating to glonal temperature is very complicated thing.
  2. Falkenherz wrote: "But, their [BEST's] statement on solar radiation seems not to be backed up by their data."

    It is for their temperature data and any solar radiation data I've ever seen other than the Soon & Briggs values of unknown provenance.

    As stated on the page I linked to, BEST ran analyses of their temperature data results against human carbon emissions, volcanic eruptions, solar variations, et cetera and found various correlations (e.g. volcanic eruptions corresponded to brief cooling spikes in a trend that otherwise matched human CO2 emissions). Offhand I'm not sure what TSI data they used, but... take your pick. There are plenty of TSI studies which show that it has declined slightly over the past several decades. Unless Soon & Briggs specify where they got their radically different 'data' there really isn't much to 'debate' here.
  3. CBDunkerson, the website you linked has no mentioning on which TSI data they used or if this is just a statement out of "common knowledge".
    However, from another commentary tread here on the article on climate time lag, there was a link to a NASA study, which seems to result in still increasing TSI.
    http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html

    I don't know if that really makes a difference, but I am still trying to learn more about TSI. As of now, I am still with the three TSI curves from three different studies as shown in figure 15 of Wang 2005; also, see my comments above.
  4. Falkenherz, the NASA study (Willson et al. (2003)) found that a slight trend (0.5%) was beginning to occur in the valleys of the 11-year cycle. As they say, "Although the inferred [total] increase of solar irradiance in 24 years, about 0.1 percent, is not enough to cause notable climate change, the trend would be important if maintained for a century or more."

    Not also that the study is ten years old. It doesn't take a precise analysis to tell that the most recent valley does not support the proposed trend.

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