Recap Of Negative Feedbacks
June 4, 2011 Leave a comment
According to Prof. Richard Lindzen, the actual variations in the Earth’s climate, in contrast to variations in current climate General Circulation Models (GCMs), are dominated by strong net negative feedbacks. Climate sensitivity is on the order of 0.5 deg. C warming for each doubling of CO2, compared with the IPCC’s value in the range of 2 – 4.5˚C. Consequently, and to paraphrase Lindzen, any such warming that may arise from increasing greenhouse gases (GHGs) would result in a surface temperature change on the order of 1 deg. C or less, which would be indistinguishable from the fluctuations that occur naturally from the myriad processes internal to the climate system itself.
To go a step further in such paraphrasing, while others such as Dr. Roy Spencer tend to agree that the real climate system is far less sensitive to CO2 than IPCC climate models predict, he also argues that there is no way to distinguish anthropogenic warming of a very sensitive climate system from natural warming within an insensitive one. Not with our current temperature data and satellite-based observations. Meaning climate scientists could be misinterpreting natural climate change as manmade.
Do Negative Feedbacks Dominate The Earth’s Climate System?
If negative feedbacks dominate, then AGW theory (which attributes the current warming to well-mixed anthropogenic greenhouse gases) is ill founded. AGW depends upon the strength of these (+ or -) feedbacks, and negative feedbacks would essentially dampen out the AGW components of any natural global warming cycles. So far, there has been no sign of a “runaway greenhouse effect”, as theorised, where positive feedbacks lead to the evaporation of all greenhouse gases in the atmosphere.
As far as the Earth’s radiation budget is concerned, there is no evidence that positive feedbacks dominate the earth’s climate system—not anything we can measure realistically and accurately. (Note: when climatologists refer to “positive feedback” they really mean “weak negative feedback”, to use electrical engineering terms.) However, there is some evidence that negative feedbacks dominate. For example, oceans could act as negatives feedbacks, as determined by cloud and water vapour, and plants in response to increases in CO2.
31 July, 2010
“Keep in mind that “feedback” in the climate system is more of a conceptual construct. It isn’t something we can measure directly with an instrument, like temperature. But the feedback concept is useful because we are pretty sure that elements of the climate system (e.g. clouds) WILL change in response to any radiative imbalance imposed upon the system, and those changes will either AMPLIFY or REDUCE the temperature changes resulting from the initial imbalance. (While it might not be exactly the same kind of feedback electrical engineers deal with, there is currently no better term to describe the process…a process which we know must be occurring, and must be understood in order to better predict human-caused global warming.)
More than any other factor, feedbacks will determine whether anthropogenic global warming is something we need to worry about.”
‘UPDATE: Further Evidence of Low Climate Sensitivity from NASA’s Aqua Satellite’ http://www.drroyspencer.com/2011/01/update-further-evidence-of-low-climate-sensitivity-from-nasas-aqua-satellite/
‘Earth itself is telling us there’s nothing to worry about in doubled, or even quadrupled atmospheric CO2’
‘Do Negative Feedbacks Dominate The Earth’s Climate System?’
‘Lindzen on negative climate feedback’
(Last modified June 6, 2011)