Posted by mhaze
It is clear warmair doesn't understand the significance of feedbacks and I'd suspect most of those who've bought the theory without too much checking don't get it either. So a quick lesson.

The warming efficiency of CO2 is logarithmic. That is, each new tonne of CO2 put in the atmosphere is a little less efficient at warming the planet than the previous tonne. The reasons are complex but are to do with the fact that CO2 only absorbs certain wavelengths. A doubling of CO2 levels from pre-industrial levels would yield a warming of around 1c.
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Ok so you have reached the point I got to 40 years ago
Now let me take you to the next step for every 1 deg C increase in temperature we get a 7% increase in evaporation. Water vapour absorbs part of the the infra-red spectrum that the lower atmosphere emits in an attempt to cool down.
This is a clear and obvious positive feedback.

The next step is that as temperatures increase we lose Arctic sea ice. Open water leads to higher rates of evaporation. Unfortunately sea water absorbs 90% of the incoming radiation as opposed to ice which reflects 90% of that radiation. So that gives us a couple more obvious feedbacks.

As regards Cohenite supposedly devastating response to one of my previous posts. I would note that being bashed around the head by a feather, rather than causing bruising usually, tends to make me laugh.

This essay and its responses have taken on a life of their own. Perhaps it was the absence of anything much to chew on other than Xmas food. Setting aside the ad homs, there are a few queries or comments that I feel the need to respond to.

Poirot and others think that too much is made of the belief/denial stuff, and Poirot calls for evidence. So do I, but plainly we point to different evidence. Given the conflicting evidence I have two responses: (1) we don't really know; and (2) some of the evidence seems more soundly based than other bits. Again, we are likely to disagree.

Warming and attribution. I agree that the planet seems to have been warming, but we can't measure the extent very well (despite all the numbers thrown around). But warming is not the issue, really. It is attribution of the warming. There is abundant conjecture about that, but no real hard evidence of the extent to which it is due to human activity.

To Sir Vivor and others: models are not evidence.

To Jeremy and others, the analogy between hearing about AGW from climate scientists and hearing medical advice from physicians is a weak one, and quite unpersuasive, as is the analogy with insurance.

And a Happy New Year to all.

warmair, another self-appointed expert says:

"Now let me take you to the next step for every 1 deg C increase in temperature we get a 7% increase in evaporation. Water vapour absorbs part of the the infra-red spectrum that the lower atmosphere emits in an attempt to cool down.
This is a clear and obvious positive feedback."

This is wrong; Clausius-Clapeyron is a description of the potential humidity capacity of warming air. One of the great myths and wrong assumptions of AGW is that with increasing temperatures evaporation will increase because relative humidity will not decrease and since water vapor is a much more effective GHG than CO2, a powerful +ve feedback is created.

In fact evaporation is not increasing as Roderick et al's latest paper shows:

http://www.sciencedirect.com/science/article/pii/S0022169411007487

Some time ago Stewart Franks explained why extra heat will not neceassarily lead to increased evaporation:

http://www.agu.org/pubs/crossref/2009/2009GL040598.shtml

Franks explains the effect:

"During drought, when soil moisture is low, less of the sun's radiant energy goes into evaporation and more goes into the heating of the atmosphere which causes higher temperatures.

"Most importantly, the elevated air temperatures do not increase evaporation but are actually due to the lack of evaporation and this is a natural consequence of drought."

Franks is supported by Taylor et al:

http://www.nature.com/nature/journal/v489/n7416/full/nature11377.html

The great Miskolzi has also noted that due to Maximum Entropy Production, when one greenhouse gas increases, CO2, another gas will decrease so outgoing radiation increases:

http://xa.yimg.com/kq/groups/16193427/157753127/name/miskolczi.PDF

Miskolzi notes water vapor levels have decreased over the last 60 years and this has been confirmed:

http://curryja.files.wordpress.com/2012/07/presentation2.jpg

In short, warmair, you don't know what you are talking about.

cohenite

The worlds surface is 70% water so what happens on the land while interesting and important does not impact on the simple fact that higher temperatures mean that you will get more evaporation.
Trying to confuse the issue with pan evaporation rates for inland Australia is not helpful.

warmair

The figures for atmospheric relative and specific hunmidity are global not just land based:

http://curryja.files.wordpress.com/2012/07/presentation2.jpg

http://www.climate4you.com/ClimateAndClouds.htm#Clouds%20and%20atmospheric%20water%20vapour

If humidity is falling where is the water being evaporated over the ocean going?

Don Aitkin,

Regarding "evidence"...

My question to you and others is, when you check the weather report, do you immediately dismiss it as a whole lot of scientists scamming you? I presume you take it for granted that meteorologists are employing their training, expertise, doing the science and delivering their predictions and projections as to the shorter-term trending weather events that will be in effect.

To the best of their ability, they are providing the service for which they have been trained.

Why is it when we are discussing long-term trends (climate) as opposed to short-term trends (weather) that the whole scenario apparently changes and "skeptics" accuse scientists of concocting a scam?