I’ve been pointing out that the “AGW likely” statements in the IPCC Summary for Policymakers aren’t bourne out by a review of the scientific literature.

This isn’t the first time that the IPCC has changed the conclusions of its contributing scientists to better suit the AGW case.

An editorial in Nature addressed this issue (“Climate debate must not overheat”, Nature 381, June 1996): “phrases that might have been (mis)interpreted as undermining these conclusions have disappeared”.

The changes made are actually stronger than indicated by the Nature editorial. You can verify the nature of these changes yourself – the original text and the changes are shown at : http://www.tech-know.eu/uploads/Spinning_the_Climate.pdf (page 10 onwards).

The consequences of a low value for CO2 climate sensitivity are more than you’re making out : if CO2 sensitivity is low, something else has driven the increases in temperature over the last two centuries.

Changes in cloud cover and solar variability (which are possibly linked) can both plunge the Earth into cooling. Needless to say, the effects of a cold Earth would be devastating, crop failures and starvation being the main worry.

Concerning Chomsky, may I point you to http://www.paulbogdanor.com/chomskyhoax.html and in particular http://www.paulbogdanor.com/chomsky/200chomskylies.pdf .
He’s incredibly dishonest – his denial of communist atrocities is on par with Holocaust denial.

I’ve seen hatred on both sides of the warming debate. On the warmist side, the warmists believe that humanity is in danger from CO2, so they feel the anti-warmists are endangering all human life with their skepticism.

The hockey stick graph was the result of a paper making a new reconstruction of the global temperature for last 1000 years.
It was given a prominent place in the 2001 IPCC report (2nd page of the Summary for Policymakers , http://www.grida.no/climate/ipcc_tar/wg1/pdf/WG1_TAR-FRONT.PDF ).
The graph was significant because it purported to show that the Earth was slowly and steadily cooling for 900 years, and then heated abruptly in the 20th century, and so could be used as powerful evidence that perhaps the increased human activity in the 20th century caused this heating. The graph was widely shown in the media as strong proof of AGW.

The graph was also controversial because it was completely different to other paleoclimate reconstructions of temperature – the hockey stick graph showed no Little Ice Age, and a greatly diminished Medieval Warm Period.

It turns out that the paper was massively flawed. Mann refused to fully divulge his methods and data for two years until Congress stepped in and forced him to do so. The investigation into his statistical methods were absolutely damning.

The IPCC of course offered no explanation or admission of this problem in their next report – as far as they were concerned, the job of the graph was done – it had convinced millions, and masses of scientists, that AGW was serious.

The accepted paleoclimate reconstructions, rather, show a much less alarming picture of similar high temperatures 1000 years ago (and even warmer periods 2000 years ago). Most significantly to my mind, they also show that the Earth has been warming for several centuries, not just the 20th century. This also coincides with increasing solar activity. The cold period of the Little Ice Age coincides with the solar quiet period of the Maunder Minimum. The smaller, more recent Dalton Minimum also created a dip in temperatures.

By removing these features of the temperature record, and their correlations with solar activity, the IPCC could then argue that it must have been human activity that caused the warming.

Therefore, the point that there are disagreements about the climate sensitivity estimate is just a statement of fact and not a convincing argument to do less to combat CC. On the contrary, the fact that we can’t hang our hats on 3c and things are as likely to be worse than this as they are better – and the costs of worse far outweigh the benefits of better – is a very good reason to start taking steps now.

I was in favour of the first ’surge’ on Iraq, after all they had invaded another country. I hardly dared say so to my liberal friends. (Today I would have the courage) But what struck me during pro and contra debates is that I saw grains of truth on both sides, which were flatly refused by the warring parties for ideological reasons.

Oliver Kamm and Chomsky. I am entirely on Kamm’s side, but Chomsky sometimes has the insight of hatred about Western capitalism.

Global warming. My impression of the anti-warmers is that they WANT to believe they are right, even before examining evidence and find the evidence that suits them. They already have the poison of hatred in their minds for reasons that have nothing to do with the subject.

In all my Google research I have found – maybe by chance – that man made climate change is generally assumed. Apparently the USA banned the use of aerosol at some point. This morning on TV news I saw Angela Merkel at a meeting at which she said the was no time to lose in stopping man made climate change. So Cameron is not alone.

Whatever the truth may be, there is no harm in limiting the emission toxic gases into the atmosphere – I have a nephew who travels around the world showing factories how they can stop or limit pollution.

Oneuniverse – thanks for sending me those links to very interesting studies. These are very weighty and serious and have no trace of political pressures in them. According to them damage to the ozone is at least partially man made.

And Oneuniverse – your letters above are examples of dispassionate observation and a valuable contribution to HP. Alas, I don’t understand them and don’t know what this hockey stick is. I’m not entirely sure whether you think climate change is to some extent man made. In one of the studies you referred to I found this sentence:

“The claim that the human input of CO2 is not an important climate forcing is found to be false in our survey.”

For the moment I believe in man made warming. No one would be happier than me if I were disproved convincingly.

This thread is on its way out alas.

I was switching between the IPCC2007 report and the CCSP 2006 report, which have different scales (C/decade and C/century), and go up to different values 0.6 and 1.2. I didn’t spot this, ended up with 0.5 C/decad.

The correct figure for the predicted warming is about 0.1 C/decade – my mistake, sorry.

AA: “Solar activity rose in the early part of the last century but has been flat or slightly lower since about 1980 – it can’t explain the continued warming since then.”

The IPCC says that there has been no significant long-term trend in insolation since 1980, but the Sun had been increasing in strength since the beginning of the century until about 1980. ie. if the IPCC had considered the period from 1970 instead of 1980, they would have seen the trend (although to be fair they were restricting their observations to satellite data – but why).

Since the oceans act as a heat buffer with a delay of perhaps 15-25 years, and a lot of the solar heating is absorbed by the oceans, the fact that the increase in insolation stopped in 1980 is no reason to dismiss the Sun’s effect in the heating that took place in the 80’s and 90’s. Also, although the increase in solar insolation stopped, the insolation level was left at a higher level than it had been before, effectively ‘turning the heat up’. I realise the magnitude of the insolation increase is uncertain, but the increasing trend since at least 1900 isn’t.

re: hockey stick

The same report that you cite also says:
“Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming.”

“Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods and because not all of the available proxies record temperature information on such short timescales.”

Please also notice the the report confirms “the high level of confidence we place in the Little Ice Age”. I also quoted from this report upthread, where it again mentions the large quantity of evidence documenting the Little Ice Age. Yet Mann’s graph is missing the Little Ice Age entirely.

The other report on the Mann paper, the Wegman report, concludes :
“Our committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”

The Wahl and Amman validation of Mann’s graph had a very low R-squared figure, making the validation meaningless. This validation figure wasn’t revealed after their paper had been accepted and published by the IPCC, which allowed them to keep the Mann hockey stick graph, although this time buried beneath a set of others in their ’spaghetti graph’ replacement for the hockey-stick (which, it needn’t be pointed out, didn’t have a hockey-stick shape, and showed evidence of the Little Ice Age again).

As for the other subsequent proxy reconstructions by Mann, Briffa etc., they all use one or more of the same recurring set of problematical proxies, such as strip-bark bristlecone and strip-pbark foxtail. The report you cited, as I mentioned earlier, specifically says that strip-bark trees should be avoided for temperature reconstructions. Mann and Briffa have ignored this advice. Also, the Yamal tree set is also used, with its well-documented problems (please see the posts in the last few months on ClimateAudit covering this.).

The majority of paleoclimate reconstructions do not have the hockey-stick shape, but instead show a warm medival period and a cool little ice age period.

These hockey stick reconstructions are just a handful in number, and they all have serious flaws. The original hockey stick was the worst, because its statistical method would create hockey stick shapes out of random red noise. This was confirmed by Dr. Wegman (see his quote upthread), and the result has been reproduced by others.

re: tropospheric heating
The radiosonde temperature records and some (but not all) of the satellite data sets don’t show the predicted warming. Also, part of the prediction is that the heating occurs from water vapour feedback, and as the papers I mentioned earlier show, upper tropospheric relative humidity has been decreasing.

This page is interesting, on significant findings from the AIRS satellite:
http://airs.jpl.nasa.gov/science/major_findings/climate/

It lists two papers that say the models are confirmed (including the Dessler 2008 paper that you indirectly mentioned), three papers that say the models are wrong with respect to water-vapour (including the Pierce paper that I mentioned), and one paper that says “The existence of radiance biases of opposite signs in different spectral regions suggests that the apparent good agreement of a climate model’s broadband longwave flux with observations may be due to a fortuitous cancellation of spectral errors.”.

I’m not really seeing the consensus that apparently exists on this topic.

It’s a fair point, if not a telling one. Following the consensus amongst scientitsts will see you right most of the time. Science, however, is decided by the evidence, not a show of hands.

Most of the scientists on-board the AGW wagon are there out of trust in the scientific establishment and its processes. It takes quite an investment of time and effort to learn the climate science and review the climate science papers, and I doubt that the members of all these scientific establishments have all studied the subject and come to a decision.

The consensus amongst the actual climate scientists also doesn’t appear to be as broad as you think eg. this survey, carried out amongst scientist who’ve contributed climate science papers to the major journals, found that 15-20% of the scientists believed that the IPCC estimate of climate sensitivity was too low, and 15-20% believed that it was too high. That’s not a consensus, but a s normal pread of opinions along the spectrum.
( http://www.jamstec.go.jp/frsgc/research/d5/jdannan/survey.pdf )

Here’s another survey, this time of scientists contributing to the IPCC 2007 report, also showing the lack of consensus : http://demanddebate.com/ipcc_survey.pdf .

I agree it’s silly to resort to a poll to determine the scientific truth, but that’s how you’re evaluating it.

The IPCC made a prediction in 2001, an absolutely key one to the AGW hypothesis, that increased CO2 will lead to increased water vapour in the mid to upper troposphere, leading to a heating of about 0.5C per decade in those regions.

These predictions were disproved by actual observations – radiosonde and satellite observations (including the corrected set). The troposphere didn’t heat as predicted, and the water vapour didn’t increase as predicted. I pointed out some of the papers documenting this earlier.

So when it comes to the published peer-review climate science, the science is not settled. Specifically, the AGW water-vapour feedback hypothesis has been disproved by real-world observations.

Thanks for your reply earlier, pressure of work prevented me from responding earlier but here are a few quick points.

Solar activity rose in the early part of the last century but has been flat or slightly lower since about 1980 – it can’t explain the continued warming since then.

The National Research Council Report largely vindicated the hockey stick, certainly WRT the data for the last 1000 years. Moreover they stated that “The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world”. It’s not just about Mann et al – there are numerous reconstruction using a variety of proxies which have very similar outcomes.

Regarding the warming of the troposphere, RSS shows a warming trend of 0.19 per decade, perfectly in line with expectations.

Finally, the IPCC estimates of climate sensitivity are based on a large number of studies based both on models and empirical observations. Even if, which I don’t neccessarily accept, water vapour feedback is overestimated, there are other feedbacks, including clouds which you correctly mention, which may not be fully represented. The Hadley Centre model does include cloud formations and shows much higher sensitivity.