Monday, March 26, 2012

New paper shows clouds have a significant negative feedback on temperature

A paper published last week in the Journal of Climate utilized satellite measurements to demonstrate that European hot summers since the 1980s are associated with a reduction in cloudiness. These observations corroborate other recent papers showing that clouds exert a negative feedback on global warming. Alarmists [such as the 'Skeptical Science' site here] hypothesize that clouds exert a net positive-feedback leading to a 'runaway greenhouse effect', but observational data from multiple papers* have shown that clouds instead exert a strong net negative-feedback cooling effect on the climate.

*Lindzen & Choi, Spencer & Braswell, Allen, Tang et al [below], others

European hot summers associated with a reduction of cloudiness

Qiuhong Tang1
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
Guoyong Leng
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China, Graduate University of Chinese Academy of Sciences, Beijing, China
Pavel Ya. Groisman
National Climatic Data Center, Asheville, NC, United States
Abstract
A pronounced summer warming is observed in Europe since the 1980s that has been accompanied with an increase in the occurrence of heat waves. Water deficit that strongly reduces surface latent cooling is a widely accepted explanation for the causes of hot summers. We show that the variance of European summer temperature is partly explained by changes in summer cloudiness. Using observation-based products of climate variables, satellite-derived cloud cover and radiation products, we show that during the 1984-2007 period Europe has become less cloudy (except of northeastern Europe) and the regions east of Europe have become cloudier in summer daytime. In response, the summer temperatures increased in the areas of total cloud cover decrease, and stalled or declined in the areas of cloud cover increase. Trends in the surface shortwave radiation are generally positive (negative) in the regions with summer warming (cooling or stalled warming), while the signs of trends in top-of-atmosphere (TOA) reflected shortwave radiation are reversed. Our results suggest that total cloud cover is either the important local factor influencing the summer temperature changes in Europe or a major indicator of these changes.

3 comments:

  1. There are different types of clouds with different radiative properties. What may be so on regional scale may not follow globally. The abstract delineates:

    "Our results suggest that total cloud cover is either the important local factor influencing the summer temperature changes in Europe or a major indicator of these changes."

    Extrapolating a regional effect to global is problematic. For the period covered in the paper (1984 - 2007), European temperatures rose by ~0.5C on average in the areas where cloud cover decreased - that is, the majority of the surface of Europe warmed significantly. We could extrapolate to conclude that global warming will overall bring less cloud cover and more heat to the surface.

    But that would be wrong, no?

    On a different note, why have you only cited papers that suggest a negative feedback from increased cloud cover? A large proportion of the literature on this topic (the majority, IIRC) favours the opposite conclusion, so your post here seems pretty one-sided.

    But perhaps there is a post here with a more comprehensive review of the literature?

    ReplyDelete
  2. 1. The authors only looked at regional data and therefore can only draw conclusions about regional effects. However, if the effect is seen regionally, it is far more likely that the same effect would be found globally than the opposite effect.

    2. "We could extrapolate to conclude that global warming will overall bring less cloud cover and more heat to the surface.
    But that would be wrong, no?" That is the opposite of the global warming theory that increased CO2 -> warming -> increased water vapor -> increased clouds & warming -> increased water vapor -> ad infinitum until the planet boils away. If such as positive feedback existed, the planet would have boiled away billions of years ago when it was much hotter.

    3. "A large proportion of the literature on this topic (the majority, IIRC) favours the opposite conclusion, so your post here seems pretty one-sided."

    Name one paper based on satellite observations, NOT computer models, that supports the notion that cloud feedback is net positive. Computer models do NOT provide data nor evidence. Observation is the hallmark of science, and that is why I cite papers based upon observations, each of which shows net negative feedback.

    ReplyDelete
  3. Monckton of Brenchley:

    I have long been impressed by Professor Lindzen's willingness to confine his presentations to the science and to avoid making policy statements. The various scientific campaigners in the UK on the climate issue who have challenged his presentation in a rather bad-tempered and unscientific manner have not really understood his central objection to the high-climate-sensitivity case, which is that the temperature feedbacks which the IPCC and its adherents assume must be strongly net-positive cannot in fact be strongly net-positive, for otherwise violent oscillations either side of the singularity in the feedback-amplification equation would have occurred at some time in the past 50 million years, but the paleoclimate evidence is that such violent oscillations have not occurred.

    The singularity in the equation occurse when the closed-loop gain in the climate system reaches unity. The IPCC's 2-4.5 K central estimates of the warming in response to a doubling of CO2 concentration imply a loop gain of 0.42-0.74. These values - dangerously close to unity - are far too high for a global temperature which, over the past 500 million years, has fluctuated by less than 3% in absolute terms either side of the long-run mean. On these and other fundamental scientific grounds Professor Lindzen questions the notion of strongly net-positive feedbacks without which the warming in response to a doubling of CO2 concentration would be little more than a harmless 1 K.The scientific campaigners try to argue with the Professor about the cloud feedback. However, as Spencer and Braswell have indicated, the cloud feedback may in fact be as strongly net-negative as the IPCC finds it net-positive. What is certain, however - and this is not fairly reflected in what the scientific campaigners have written - is that the IPCC itself says clearly that the behavior of clouds is one of the greatest uncertainties in the determination of climate sensitivity.

    Furthermore, Professor Lindzen has demonstrated not once but twice that the outgoing longwave radiation which the official theory says should be trapped in the troposphere by manmade greenhouse gases is escaping to space much as normal, suggesting a climate sensitivity of 0.7 K per CO2 doubling, in line with Spencer and Braswell, and implying net-negative temperature feedbacks.

    ReplyDelete

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