It’s the Sun, Stupid

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


Objection:

The sun is the source of all the warmth on earth. Any increase in temperature is most likely due to changes in solar radiation.

Answer:

It’s very true that the earth is warmed, for all practical purposes, entirely by solar radiation. So if the temperature is going up or down a reasonable place to find the cause would be the sun. Well, it turns out that it is more complicated than one might think to detect and measure changes in the amount or type of sunshine reaching the earth. Detectors on the ground are too susceptible to all kinds of interference from the atmosphere. After all, one good cloud passing overhead can cause an instant shiver on an otherwise beautiful, warm day, but not because the sun itself changed. The best way to detect changes in the actual output of the sun versus changes in the radiation reaching the earth’s surface because of clouds, smoke, dust or pollution is by taking readings from space.

This is a job for satellites. According to PMOD at the World Radiation Center there has been no increase in solar irradiance since at least 1978 when satellite observations began. This means that for the last thirty years, while the temperature has been rising fastest, the sun has shown no trend.

There has been work done on reconstructing the solar irradiance record over the last century before satellites were available. According to the Max Plank Institute where this work is being done, there has been no increase in solar irradiance since around 1940. This reconstruction does show an increase in the first part of the 20th century that coincides with the warming from around 1900 til the 1940’s. This trend in irradiance is not enough to explain it all, but it is responsible for a large portion of that trend in temperature. See this chart of the observed temperature, the modelled temperature and the variations in the major forcings that contributed to 20th century climate.

Real Climate has also done a couple of detailed discussions both about what the conclusions about solar forcing are, as well as exactly how they were arrived at. Read them here and here.


This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


“It’s the Sun, Stupid” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

203 thoughts on “It’s the Sun, Stupid

  1. Here’s the new study in *Nature* with the surpising finding that even in recent down solar cycle years, when UV radiation decreases, visible light into the atmosphere actually increases. It could be responsible for moderate warming and introduce a new modeling complexity in understanding climate.

    http://www.cnn.com/2010/WORLD/europe/10/07/solar.study.climate.change/index.html?hpt=Mid

    For simple country quote miners like myself this, I guess, is the zinger:

    “They [the solar cycles] are contributing nothing to long-term global warming,” she [lead authorJoanna Haigh] said, “and it has no bearing on what we understand about greenhouse gases and their influence on climate.”

    I have institutional access to *Nature*, which is “paywalled”, as Chris might say, but (a) I couldn’t follow the methods anyway, and (b) it would be unethical (obviously) for me to cut and paste it, but here’s the abstract:

    Nature 467, 696-699 (7 October 2010)

    An influence of solar spectral variations on radiative forcing of climate

    Joanna D. Haigh1, Ann R. Winning1, Ralf Toumi1 & Jerald W. Harder2

    Abstract

    The thermal structure and composition of the atmosphere is determined fundamentally by the incoming solar irradiance. Radiation at ultraviolet wavelengths dissociates atmospheric molecules, initiating chains of chemical reactions—specifically those producing stratospheric ozone—and providing the major source of heating for the middle atmosphere, while radiation at visible and near-infrared wavelengths mainly reaches and warms the lower atmosphere and the Earth’s surface1. Thus the spectral composition of solar radiation is crucial in determining atmospheric structure, as well as surface temperature, and it follows that the response of the atmosphere to variations in solar irradiance depends on the spectrum2. Daily measurements of the solar spectrum between 0.2 µm and 2.4 µm, made by the Spectral Irradiance Monitor (SIM) instrument on the Solar Radiation and Climate Experiment (SORCE) satellite3 since April 2004, have revealed4 that over this declining phase of the solar cycle there was a four to six times larger decline in ultraviolet than would have been predicted on the basis of our previous understanding. This reduction was partially compensated in the total solar output by an increase in radiation at visible wavelengths. Here we show that these spectral changes appear to have led to a significant decline from 2004 to 2007 in stratospheric ozone below an altitude of 45 km, with an increase above this altitude. Our results, simulated with a radiative-photochemical model, are consistent with contemporaneous measurements of ozone from the Aura-MLS satellite, although the short time period makes precise attribution to solar effects difficult. We also show, using the SIM data, that solar radiative forcing of surface climate is out of phase with solar activity. Currently there is insufficient observational evidence to validate the spectral variations observed by SIM, or to fully characterize other solar cycles, but our findings raise the possibility that the effects of solar variability on temperature throughout the atmosphere may be contrary to current expectations.

    It might be too early to expect any widespread reaction, but I’ve already done a preliminary scan of the denialsphere to see how the article would be received and only found this so far–a rant from a nobody at the lead author. The guy is likely insane, and certainly has no clue what the article is or is not saying.

    If one goes back in history no matter what time period without exception when the sun displays low solar activity the temperatures of earth always goes down, but time lags are on the order of several years .

    . . . Your study, the CO2 man made global warming hoax, don’t mean anything because in the next few years we will know ,who is right and who is wrong.

    http://climaterealists.com/index.php?id=6428

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  2. Some interesting studies for those who wish to do some reading (with thanks to skepticalscience):

    •Erlykin 2009: “We deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to solar activity is 14% of the observed global warming.”

    •Benestad 2009: “Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.”

    •Lockwood 2008: “It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is -1.3% and the 2? confidence level sets the uncertainty range of -0.7 to -1.9%.”

    •Lean 2008: “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…”

    •Lockwood 2008: “The conclusions of our previous paper, that solar forcing has declined over the past 20 years while surface air temperatures have continued to rise, are shown to apply for the full range of potential time constants for the climate response to the variations in the solar forcings.”

    •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.”

    •Lockwood 2007: “The observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanism is invoked and no matter how much the solar variation is amplified.”

    •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.”

    •Scafetta 2006 says “since 1975 global warming has occurred much faster than could be reasonably expected from the sun alone.”

    •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.”

    •Solanki 2004 reconstructs 11,400 years of sunspot numbers using radiocarbon concentrations, finding “solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades”.

    •Haigh 2003 says “Observational data suggest that the Sun has influenced temperatures on decadal, centennial and millennial time-scales, but radiative forcing considerations and the results of energy-balance models and general circulation models suggest that the warming during the latter part of the 20th century cannot be ascribed entirely to solar effects.”

    •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.”

    •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.”

    As Ray Pierrehumbert – Louis Block Professor in Geophysical Sciences at the University of Chicago – said in response to a quote in Nature which said that this was the ‘last nail in the coffin’ for solar enthusiasts about solar warming:

    “That’s a coffin with so many nails in it already that the hard part is finding a place to hammer in a new one.”

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