Study: Sun’s contribution to recent warming is “negligible”

Earth to deniers — global warming is caused by human emissions, not solar activity.

The Naval Research Laboratory and NASA report that, “if anything,” the sun contributed “a very slight overall cooling in the past 25 years.” D’oh! The study, “How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006,” finds:

Empirical models that combine natural and anthropogenic influences (at appropriate lags) capture 76% of the variance in the monthly global surface temperature record, suggesting that much of the variability arises from processes that can be identified and their impact on the global surface temperature quantified by direct linear association with the observations.

Natural influences produce as much as 0.2 K warming during major ENSO events, near 0.3 K cooling following large volcanic eruptions and 0.1 K warming near maxima of recent solar cycles. To properly quantify their amplitudes, the natural and anthropogenic changes must be accounted for simultaneously when analyzing the surface temperature anomalies, since neglecting the influence of one can overestimate the influence of another. For this reason, we suggest that estimated solar cycle changes of 0.2 K and Pinatubo cooling of 0.4 K are too large.

None of the natural processes can account for the overall warming trend in global surface temperatures. In the 100 years from 1905 to 2005, the temperature trends produce by all three natural influences are at least an order of magnitude smaller than the observed surface temperature trend reported by IPCC [2007]. According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years…

Here are some excellent visual “reconstructions of the contributions to monthly mean global surface temperatures by individual natural and anthropogenic influences (at appropriate lags) are shown”:


The right hand ordinates give the native scales of each influence and the left hand ordinates give the corresponding temperature change determined from the multiple regression analysis. The grey lines are trends for the whole interval. The inset in Figure 2d shows the individual greenhouse gases, tropospheric aerosols and the land surface plus snow albedo components that combine to give the net anthropogenic forcing.

What is significant about this analysis is that it is based on observations:

To distinguish between simultaneous natural and anthropogenic impacts on surface temperature, regionally as well as globally, we perform a robust multivariate analysis using the best available estimates of each together with the observed surface temperature record from 1889 to 2006. The results enable us to compare, for the first time from observations, the geographical distributions of responses to individual influences consistent with their global impacts.

Again, this is not really a big surprise to those who follow the scientific literature. A major 2007 study concluded:

Here we show 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.

Since the notion that changes in some spots or solar output has been the primary driver — or even a large component — of recent warming remains perhaps the biggest myth pushed by deniers, let’s look at some more analysis. The excellent debunking website, Skeptical Science, has a nice post on this. They explain that “The study most quoted by skeptics actually concluded the sun can’t be causing global warming.” Double D’oh!

And they list a bunch of other studies dismissing or minimizing the sun’s contribution:

  • Ammann 2007: “Although solar and volcanic effects appear to dominate most of the slow climate variations within the past thousand years, the impacts of greenhouse gases have dominated since the second half of the last century.”
  • Foukal 2006 concludes “The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years.”
  • Usoskin 2005 conclude “during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source.”
  • Stott 2003 increased climate model sensitivity to solar forcing and still found “most warming over the last 50 yr is likely to have been caused by increases in greenhouse gases.”
  • Solanki 2003 concludes “the Sun has contributed less than 30% of the global warming since 1970.”
  • Lean 1999 concludes “it is unlikely that Sun-climate relationships can account for much of the warming since 1970″³.
  • Waple 1999 finds “little evidence to suggest that changes in irradiance are having a large impact on the current warming trend.”
  • Frolich 1998 concludes “solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade”

Only a pagan would continue to worship at the altar of the sun-explains-everything religion.

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17 Responses to Study: Sun’s contribution to recent warming is “negligible”

  1. rjm says:

    Global Fogging.

    It’s all the little up and down turns that create confusion. We want to see a nice steady even and increasing progression of warming with hardly a ripple. That would help us to eliminate other factors and causes.

    Instead of that, we have the current confusion of the past 10 years. We have meteorologists telling us that there is a cooling effect in place right now and sea ice development way ahead of last year etc.

    So Ocean currents and Sun changes stir things up quite a bit to the point where average folks like me, not having our noses in science textbooks all day long, look at GW and mostly see fog.

  2. Bob Wallace says:

    Well, rjm, if you don’t have the ability to read the data then you’re left to depend on the interpretation of others.

    Now who do you think the person/group to trust – thousands of climate scientists, including NASA people, or a senator from Oklahoma and the guy who started the Weather Chanel?

    Who qualifies to fly the plane on which you’ve reserved a seat? Certified pilot or keyboard whacker?

  3. Yes but... says:

    Then what caused MWP and LIA? Sure, you must have an appropiate answer.

  4. Dano says:

    Now who do you think the person/group to trust – thousands of climate scientists, including NASA people, or a senator from Oklahoma and the guy who started the Weather Chanel?

    Why, the person who utters phrases that are consistent with the confirmation bias of an ideological worldview, not biased scientists of course.

    Priorities, man!



  5. Earl Killian says:

    I’ve even run into crazies that claim the run-up in greenhouse pollution was good because it would prevent the next ice age. I guess they never saw Figure S2 of Hansen’s Target Atmospheric CO2 : Where Should Humanity Aim?

    Note to crazies: we’ve already added more CO2 to the atmosphere than the difference between ice age and interglacial and we’re still adding 2.2 ppm per year.

  6. tidal says:

    I don’t even see how the sun could have any effect on our climate whatsoever. When I look up in the sky, it seems to me that the sun represents only about 0.001% of the total area. That just seems to be too small to matter. Same goes for CO2. How can something that is only 0.04% of the atmosphere affect our climate? I am sure we can all see this is just common sense. Many distinguished scientists think that the climate is controlled by volcanoes.

    We have much more important issues to deal with, many of which are not even being discussed during the election. For instance, for several months now I have noticed that the sun is turning off earlier and earlier each day, and yet I have not seen a single TV news program even mention it.

  7. Joe says:

    Yes, but — MWP and LIA do not appear to be globlal, but mostly North American, as I’ve previously blogged (see “Sorry deniers, hockey stick gets longer, stronger: Earth hotter now than in past 2,000 years”).

    If you read all the studies above, it would appear that the sun and volcanoes are mostly responsible for the temperature changes in earlier times.

  8. David B. Benson says:

    Yes but… — I suggest reading W.F. Ruddiman’s “Plows, Plagues and Petroleum”.

    Joe — Actually both MWP and LIA appear in various regional proxies around the globe, although not precisely synchrounous with Europe. For example, liminological records from Patagonia show an MWP.

  9. gaiasdaughter says:

    Hmm, okay . . . as a pagan, I do take issue with your last statement. Luckily, I have a thick skin.:)

  10. mauri pelto says:

    Excellent article thanks for highlighting it. Nothing surprising, but just an incrementally better resolution and comprehensiveness to the analysis. This does not focus on LIA or MWP, but David is correct the LIA signal is robust in the Southern Hemisphere with glacier advances in the Andes, New Zealand, New Guineau, Kilimanjaro and in Asia throughout the Himilaya. This does not mean it was the same magnitude every where, but the lowering of glacier snowlines was pretty comparable in the aforementioned areas to Western NA or the Alps.

  11. Steve Bloom says:

    Joe, the link to the abstract isn’t very useful since it just gets to the AGU sign-on screen.

    GISS has both the abstract and the complete paper here.

  12. Joe says:

    Steve — Good catch. Fixed.

  13. John Mashey says:

    Yes but:

    I second David Benson’s suggestion to read Ruddiman, who offers several hypotheses that could explain some of the temperature jiggles of the last 2000 years, i.e., that plagues caused reforestration before the MWP and afterwards, and reforestration = less CO2 = cooler. He has several newer papers beyond the book as well.

    Meanwhile, people also might read How to learn about science, if the progression from idea to hypothesis to strong theory is unfamiliar.

    Also mentioned there, I recommend:

    [SEL2004] Richard C Selley, The Winelands of Britain: Past, Present & Prospective, 2004 (F).

    Geologist/oenophile traces historical growth and shrinkage of UK wineries over two millennia. Current wineries are North of Medieval Warm Period and heading North quickly. Slightly out of date, a few vineyards are already in Leeds, Selley’s projection for 2050. Visit the Loch Ness winery around 2100AD. There is now a newer 2nd Edition with more detailed projections of which grapes will grow where.

    Our future temperatures depend in *no way whatsoever* on whether or not it’s already warmer than MWP or not, but Selley’s research strongly supports the idea that it’s warmer (in UK at leasty) now than it was in MWP or Roman periods, given that wine is a high-value product, and people produce it where they can.

    Selley now worries that by 2080, Southern England wil lbe *too hot* for good grapes…

  14. Erl Happ says:

    For an entirely different viewpoint based on a careful analysis of the data see:

  15. Jim Eager says:

    Re Yes, but…. and the MWP and LIA,
    The Lean and Rind 2008 paper does not say that solar variation does not affect climate, they find that it has not been the major factor in the past 100 years, and has been negligible over the last 25, but then if you bothered to read even the excerpt in Joe’s post you would know that.

  16. paulm says:

    Has anyone set up a clock showing the declining ice volume?

    Here is more evidence of GW from Canada….
    Arctic Meltdown Signals Long-Term Trend

    “We were really surprised at how fast some of the ice shelves broke away,” he said.
    “How could an entire ice-locked fjord become ice-free in days? I couldn’t believe it was just gone,” Copland recalled.

    In total, five ice shelves of Ellesmere Island lost 23 percent of their ice — 214 sq km — during this year’s short Arctic summer.

    “The ice shelf decline is far worse than our worst estimations,” he said.

    “I’d be surprised if there are any ice shelves left in 10 years,” Copland said.

  17. shop says:

    Well, rjm, if you don’t have the ability to read the data then you’re left to depend on the interpretation of others.

    Now who do you think the person/group to trust – thousands of climate scientists, including NASA people, or a senator from Oklahoma and the guy who started the Weather Chanel?

    Who qualifies to fly the plane on which you’ve reserved a seat? Certified pilot or keyboard whacker?