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Mike

First question: how much of that increase is due to natural recovery from the Little Ice Age?

Good question. How long does the recovery go on? How do we quantify it?

More to the point, how does the recovery cause energy to accumulate in the climate system?

Since the paleoclimatologists seem quite happy with data which say that CO2 levels are at their highest for 300,000 years, estimating the degree of warming that took place going into the Mediaeval Warm Period should be relatively easy.

No one argues that the MWP was caused by CO2.

This has no bearing on the argument that current warming is caused by CO2.

This is a very important distinction.

Jul 30, 2011 at 11:14 PM | Unregistered CommenterBBD

The scientifically sceptical argument centres on the extent to which the direct forcing by CO2 will be amplified by positive feedbacks (eg more water vapour; reduced ice albedo) or offset by negative feedbacks (eg increased low cloud over major ocean basins). This is the 'climate sensitivity' argument.
So it's now 200 years since "pre-industrial times"; the concentration of CO2 in the atmosphere has increased from 1:3571 to 1:2564; the temperature (assuming the data are accurate which appears to be open to debate) has risen by about 0.8C. And that also assumes it is possible accurately to measure the earth's temperature to that precision and that the variation is not in fact lost in the noise.
First question: how much of that increase is due to natural recovery from the Little Ice Age? Since the paleoclimatologists seem quite happy with data which say that CO2 levels are at their highest for 300,000 years, estimating the degree of warming that took place going into the Mediaeval Warm Period should be relatively easy.
Once that figure has been determined it also ought to be possible to establish (given all the research, the data, and the funds that have been flung at the problem in the last 20 years) whether the feedback is positive or negative instead of two sides essentially firing opinions and insults at each other across a scientific no-man's-land.
And I'm sorry to say, BBD, that paleoclimatology is going to be judged by the hockey stick fiasco because that was not a one-off. Paleo data -- some of it the same data that have already been effectively proved unreliable by those with less of an axe to grind than the Usual Suspects -- continue to be used and continue to be defended by those same people.
Meanwhile we have Spencer & Braswell to consider, not to mention Svensmark's work on cosmic rays and clouds (and a CERN report which I'm sure we all await with interest).
The link you provided for me to RealClimate was useful (thank you) as far as it went but within the first couple of paragraphs, I found two instances of the word "could", an admission that CO2 had not caused the first 800 years of warming as seen in the Vostok cores but "could" have accounted for the rest, and a "probable" scenario.
As I've said, on that basis we are going to wreck civilisation on earth?
I don't think so.

Jul 30, 2011 at 10:03 PM | Unregistered CommenterMike Jackson

Eccesiastical Uncle

My apologies - this should read:

(1) As regards the physical properties of CO2 - there is no informed controversy. The no-forcings no-feedbacks estimate for the effect of a doubling of CO2 over pre-industrial levels on global average T is +1C.

Jul 30, 2011 at 9:53 PM | Unregistered CommenterBBD

Eccesiastical Uncle

I'm glad someone reads the references ;-)

Your questions:

(1) As regards the physical properties of CO2 - there is no informed controversy. The no-forcings estimate for the effect of a doubling of CO2 over pre-industrial levels on global average T is +1C.

The scientifically sceptical argument centres on the extent to which the direct forcing by CO2 will be amplified by positive feedbacks (eg more water vapour; reduced ice albedo) or offset by negative feedbacks (eg increased low cloud over major ocean basins). This is the 'climate sensitivity' argument.

(2) The extent to which global political agreement can restrain CO2 emissions is not clear. But to date, the indications are not encouraging.

(3) A truly gigantic effort to displace coal from electricity generation globally could head off the worst likely effects. This would require huge build rates for baseload nuclear plant (Gen III). Gas will also be required for load following and peak plant.

Renewables are not likely to be resource, cost, footprint, efficiency or reliability effective in the short- and mid-term. As such, I suspect they represent a dangerous false promise.

Paleoclimatology should not be judged by the standards of the Hockey Stick debacle. A handful of bad or misguided papers does not bring an entire field into disrepute.

Jul 30, 2011 at 7:44 PM | Unregistered CommenterBBD

Richard Betts

'So the points I have discussed vary in confidence level - the first 2 points are more certain, the last 2 less so.'

Arctic sea ice is melting. Since 1900, global sea levels have risen by more than eight inches. Do we not expect rising sea levels to happen when coming out of a little ice age?

Research suggests human action doubled the risk of the 2003 European heatwave.
And climate change made the autumn 2000 floods in the UK about twice as likely.

Your uncertainties become fact to the politicians. I would be highly surprised if you presented details to the government linking regional weather to climate change due to AGW/nonAGW model outputs for your data.

Minesterial Statement:
'The amount of carbon dioxide in our atmosphere is rising. Concentrations of CO2 have grown by 40% since pre-industrial times. Two thirds of that increase has happened in the last 50 years.

With all this extra greenhouse gas floating about, we would expect the Earth's surface to get warmer. And so it has: by about 0.8 degrees in the last century.'

Cause:Effect. No confidence levels, no possibility of complex cause purely extra greenhouse gas has caused Earth's surface to warm by 0.8 degrees.

Would you validate the ministers statement Richard please, upon your return?

Jul 30, 2011 at 3:33 PM | Unregistered CommenterLord Beaverbrook

Lord Beaverbrook

Chris Huhne's statements on Arctic sea ice melt and sea level rise are backed up by evidence - observations from satellite, tide gauges etc. For sea ice, we are more confident about sea ice extent than thickness. Summer Arctic sea ice extent is declining, on average, but with year-to-year variability. Lucia is taking bets on this year's minimum, if you read her blog!

Drought is more tenuous and comes down to some extent to how it is defined - drought really can only be defined locally as it the driest fraction of time that a certain location experiences, and this of course varies from location. A drought in the UK is not a drought in Australia, for example. I think (but I have not checked) that Mr Huhne's speech must be referring to droughts as defined locally.

The statements on the summer 2003 heatwave and autumn 2000 floods are based on work by my colleagues. It depends on being able to estimate what the climate of the present day would have been without the influence of humans, so of course this depends on our computer models. Personally I think these are good pieces of work but they do of course rely on a lot of assumptions.

So the points I have discussed vary in confidence level - the first 2 points are more certain, the last 2 less so.

I'm away for the next week but look forward to joining the conversation again when I get back!

Jul 30, 2011 at 2:20 PM | Unregistered CommenterRichard Betts

Mike,

Personally I don't think that "catastrophe is about to ensue" although I do think anthropogenic climate change is a serious issue for the longer term. For the nearer term I think we can adapt to the changes that are in the pipeline, and indeed we're going to have to because some further change is probably already inevitable.

Much of the issue is about impacts on people and how fast we can react to changes - as you say, when you look at long-term states of the climate, the Earth has seen much higher CO2 than today and been considerably warmer, and life as a whole didn't come to an end. But equally, rapid climate changes in the past have led major shocks to the system which were bad for individual life forms and even whole species or groups of species. So evidence from the past suggests that the climate can change enough to have big effects, and while this can of course happen naturally, it also (in my opinion) it makes sense to not increase the chances of this through our own influence. Of course this also has to be offset against the direct consequences of minimising our influence! I personally don't really think there is strong evidence for major "catastrophic" upsets in the near future though.

Jul 30, 2011 at 2:08 PM | Unregistered CommenterRichard Betts

Chris Huhne's latest propoganda. I wonder where he gets these Idea's from eh!

It is a compelling picture, and one supported by a growing body of evidence.
Arctic sea ice is melting. Since 1900, global sea levels have risen by more than eight inches.

Severe droughts are now twice as common as they were in 1970.
Research suggests human action doubled the risk of the 2003 European heatwave.
And climate change made the autumn 2000 floods in the UK about twice as likely.

Every major scientific institution in the world concurs: the Royal Society, the US National Academy of Sciences, the Academie des sciences. Change on this scale cannot be explained by anything else.

There is no computer model of world temperature and climate that can explain what has happened without greenhouse-gas induced global warming. None.

http://www.businessgreen.com/bg/opinion/2095836/chris-huhnes-art-science-climate-change-speech

Jul 30, 2011 at 12:15 PM | Unregistered CommenterLord Beaverbrook

The BBC sticking up for sceptics, against an ex UEA scientist who calls non concensus scientists sceptics, non scientists deniers and the whole 1% who are not on board lunatics. 12 mins in.
Trenberths missing heat taken out of context in the 'leaked' emails.

http://www.bbc.co.uk/iplayer/episode/p00j2bgs/One_Planet_China_green_champion_at_home_but_looter_abroad/

Utter pratt!

Jul 30, 2011 at 12:00 PM | Unregistered CommenterLord Beaverbrook

Richard
Once again, thankyou for taking the time to explain.
I am still trying to puzzle over why, when the CO2 content of the atmosphere is pretty close to the lowest it has been for 300 million years we are expected to believe that catastrophe is about to ensue. You talk about positive feedbacks but there are those who say the feedback is equally likely to be negative and neither the "Plussers" nor the "Minussers" in this argument appear to be able (or willing) to do other than assert. This is not the empirical evidence that I would be looking for before I told government "the sky is falling" and I was obliged to spend trillions of dollars/pounds/euros on what seems very likely to be a non-problem and to alter totally the lives of everyone on the planet on the basis of sophisticated guesswork which only the last 30 years of technological development have enabled us to even start thinking about.
I refer, of course, to your supercomputer which like my Commodore 64 (of blessed memory) is only as good as the program. The only difference is yours can churn out the garbage several million times faster!
On the other hand I do see a number of people -- some with scientific qualifications and some without -- who have the ear of government and are using their access to push a very definite socio-political agenda. If we could move them out of the way and leave the field clear for some genuine scientific activity that is more open to hypotheses other than those that pre-suppose a certain outcome then we might not be having this battle.
Even RealClimate, to which BBD directed me, admits that the the initial warming discovered by the Vostok cores was not caused by CO2 and that the rest "could" have been and that the "probable" sequence of events was as they describe it.
But they then go on to talk about the "heat-trapping" properties of CO2 and I ask what heat-trapping properties are so special to a gas that represents barely 0.004% of the atmosphere that the whole of civilisation has to be up-ended to combat it.
Only I can't ask that question of the majority of climate scientists because if I do they, unlike you Richard and a few others, scream "heretic", "denier", "oil company shill" at me. And that makes me quite upset and even more determined that one day I will find out why they are so insecure in their beliefs that they behave like that.
Meanwhile, have a nice weekend ((;¬)

Jul 30, 2011 at 10:06 AM | Unregistered CommenterMike Jackson

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