Johnj

You comment about the Greenland ice sheet taking 1000 years to melt. Estimates like that are based on computer simulations. Sceptics are usually quite critical of computer modelling, but all the sceptics commenting on ice sheets accept without question the accuracy computer models in this application. This is surprising, because computer models predicting increased polar snowfall and 1000 year melt times for ice sheets dont seem to match the observations.

http://www.commondreams.org/views06/0217-22.htm

http://www.livescience.com/environment/060810_antarctic_precip.html

There is an extraordinary amount of cherry-picking and outright misrepresentation and misdirection coming from all sides on this debate. The question isn't whether CO2 has an effect on global temperatures, but to what extent, and what should be done about it. People are labelled "skeptics" or "denialists" merely for questioning figures and projections. These terms have no useful meaning, unless you believe in the completely non-scientific idea that we ought to just embrace the IPCC projections, or at least those IPCC projections that a particular lobby wants us to accept.

To deal with a couple of points raised above. Fester claims that the paper he cites shows that the Arctic warming of the 30s was limited to a "small area". Wrong. It says that it occurred above latitutde 60 degrees. The study he cites, while acknowledging difficulties with early century temperature measurements, draws on Eurasian based thermometers to say that the heat extended further down in the 90s, than in the 30s. This hardly negates Carbonari's point.

Fester also cites a BOM report to prove that Tuvalua and Kiribati are sinking below the oceans. The Gore claim was that the islanders had been forced to evacuate to New Zealand, and is completely false. Sea level is rising in the area, but how much due to global warming is conjecture. Kiribati is experiencing sea level increases of 6 mm per year, but Fiji only 2.7 mm. Obviously there's fair bit of movement in the earth's crust around this area.

As for support for Mann et al. The links provided by Fester hardly amount to a ringing endorsement. They say that the NRC finds the Mann et al results "plausible". They don't appear to rebut the fact that the algorithms Mann used result in it graphing even random numbers as a hockey stick. And they contradict the scientific consensus of the Medieval warm period, as well as the Little Ice Age.

I find the criticism of Wegman for not being a climate scientist whimsical, particularly when someone can quote John Quiggin as an expert, when he's not even a scientist at all!

A worthwhile perspective on the scientific debate on climate change can be found here. http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000641reflections_on_the_c.html

"Interestingly enough, the response from Steve McIntyre is completely in agreement with RealClimate contributors Stefan Rahmsdorf and William Connelley that the "hockey stick" debate is pretty much irrelevant to the scientific question of whether or not greenhouse gases will affect the future climate."

So can we all please forget about the "hockey stick" and get on with the policy changes that are needed.

GrahamY, I was being tongue in cheek when I said I always accept what Quiggin says, although I find he's more often right than wrong. I don't characterise him either as a scientist or a non-scientist. It depends on how you regard economics as a field. I would say, however, that he has an impressive grasp of mathematics.

Also a distinction could be made between 'denialists' and 'sceptics' about AGW. One can be either or both as long as one supports one’s position.

Fashion is not the right word, but I'm also aware that certain paradigms can be firmly established only to be overturned later. Hansen has been to the fore in warning about ice-sheet melting and sea-level rise, departing from IPCC 1. He keeps saying that he hopes he is wrong. We should too, but he's also passionate about following the science. For example, in 1989 he refused to give Gore images of increased drought generated by their computer models because he didn't at that time sufficiently trust the model's estimate of precipitation.

There were one or two things that I thought Gore may have gotten wrong in the film, Pacific Islanders having to flee to New Zealand being one of them, but to dwell on them in the review would have been picky and given the wrong impression.

I can't see why indigo considered it appropriate to brand Gore a 'liar', even if he had been wrong about 2005 being the hottest year. It would have been more scientific to consider other explanations, like being incorrectly informed. To be honest an unjustified accusation like that reflects on the reliability of the author and the ability to respond to evidence in an unemotional way. Nevertheless indigo did raise some issues which I hope to comment about in due course.

Forget about the "Hockey Stick"? What you should realise Johnj is that the "Medieval Warm Period", the "Little Ice Age" and attacking the "Hockey Stick" form a Holy Trinity for denialists. Do a search and you will realise that almost every denialist website is on a quest to "prove" the first two to be global events and the third to be a fraud. It is sad to see what probably started as scepticism degenerate into a quasi-religious fanaticism.

Ultimately, observations are all that matter. What you want things to be is irrelevant.

Indigo mentioned that Hansen had spoken of 2C temperature increase by 2050. I’m not sure whether that is so. I understood his expectation was for 3C by 2100 on a ‘business as usual’ basis. This is based on the forcing implied in doubling CO2 which is estimated to be 4 watts/m2. He sees the equilibrium sea level response to 3C as 25 metres (80 feet), plus or minus 10 metres. This will not happen by 2100, but he sees it as happening in centuries rather than millennia, reminding us that the about 14,000 years ago sea levels rose 20m in 400 years, or 5m per century.

He outlines his reasoning in the editorial essay in <i>Climate Change</i> last year (http://www.columbia.edu/~jeh1/hansen_slippery.pdf).

How much warming should be considered ‘dangerous’ in part subjective. Many scientists seem to think 2C will be OK. Hansen and his associates would like to see it limited to 1C. As I understand it this would mean slamming on the brakes rapidly because 1C is almost certain in the next 50 years from forcings already in the system.

Their reasoning may be found in a 2005 paper. Go to the abstract at http://pubs.giss.nasa.gov/abstracts/submitted/Hansen_etal_1.html and download the large pdf file from there.

I suspect that 2C would not be impossible when you consider, as Flannery tells us, that China and India are building 1400 coal-powered power stations in the 2000-3030 period. That’s one every 8 days. Hansen says that we should be building no conventional coal power stations after 2012 in the developed countries and after 2022 in the developing countries. He’s assuming that geosequestration of CO2 will work. From 2025 we should be bull-dozing conventional coal-fired power stations.

If you have good downloading facilities (ie broadband) I’d recommend the slides for his National Academy of Sciences lecture:

http://www.columbia.edu/~jeh1/nas_24april2006.pdf

It has some wonderful maps showing the implications of sea-level rises in some of the main population centres. I’d also recommend the following slide of climate forcings (a variant of one of the 50 slides in the NAS lecture):

http://www.realclimate.org/images/forcing_1750-2000-toppanel.jpg