Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
The Hockey Stick was invented by Michael Mann, not Hansen. Hansen made a few temperatures predication back in the day when he started working for Al Gore. Needless to say they were all a failure.

by Luis de Sousa (luis[dot]de[dot]sousa[at]protonmail[dot]ch) on Sat Feb 5th, 2011 at 12:16:23 PM EST
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Thanks for the correction. I assume the failure to which you refer is the failure to convince TPTB.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sat Feb 5th, 2011 at 12:21:57 PM EST
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Hansen's global temperature projections, particularly the ones he made in 1988, are not particularly great. The below picture is from a 2009 Real Climate post on that claim.

Key mistake in his 1988 estimates was using a higher climate sensitivity. With the current uptick in global temperatures last year, we're back into Hansen's scenario C, but just barely.

What always frustrates me in this particular topic that's beaten to death, particularly on sceptic websites, is that I can't seem to find a graph like this with standard deviations added. And of course Hansen has made other projections since.

Yet, at first glance, the temperature records are indicating so far that Hansen's 1988 projections weren't too good.

by Nomad on Sat Feb 5th, 2011 at 04:41:14 PM EST
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If these are 1988 predictions given the limitations, how are they a failure? I mean compared to who else who was making projections at the time? As you point out scenario C is on track. In 1988 I assume that climate modeling was much less nuanced. That one of his 1988 scenarios is absolutely compatible with the data is spectacular it seems to me.
By the way Real Climate has updated their model-data comparisons including the Hansen 1988 model, here.

The road of excess leads to the palace of wisdom - William Blake
by talos (mihalis at gmail dot com) on Sun Feb 6th, 2011 at 07:07:39 AM EST
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Scenario 3 is unrealistic - see the reply to comment #3 at that post.
by det on Sun Feb 6th, 2011 at 07:13:42 AM EST
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Oops ... "C"
by det on Sun Feb 6th, 2011 at 07:14:08 AM EST
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Regarding the value of the models, see the reply to comment #1.
by det on Sun Feb 6th, 2011 at 07:19:27 AM EST
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Yep, I shouldn't have skipped the discussion. Thanks!

The road of excess leads to the palace of wisdom - William Blake
by talos (mihalis at gmail dot com) on Sun Feb 6th, 2011 at 07:23:21 AM EST
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I didn't write they are a "failure", I wrote that they aren't good. And Hansen's 1988 models are beginning to show that they weren't good enough in modeling reality. That's no big deal to me, but climate scientists (and hence also sceptics) still seem to think it is - otherwise it wouldn't be a topic every year at Real Climate. And not much surprise there: Schmidt works for Hansen.

And no, the argument that scenario C matches global temperatures, doesn't hold water. Because scenario C was based on drastic reductions of atmospheric greenhouse gasses between 1990 and 2000. That didn't happen. In terms of greenhouse gasses exhaust, we follow scenario B. (Hansen first calculates how much extra forcings the earth will get, and bases temperature projections on these calculations.)

So in forcings we track Hansen's scenario B, but even without reductions in GHG, the global temperature barely reaches the line of scenario C at this point. Still, as previously said, we actually can't be really sure about this as the picture doesn't include standard deviations.

Even the recent Real Climate post you link to admits that Hansen's preferred scenario, B, is running out of sync with measurements. (Actually, Hansen stated in 1987 that he was thinking it would turn out to be in between A and B.)

Therefore, the issue is climate sensitivity. Again. It's the single most important figure in climate science, and it is not settled. Despite Gavin's proclamation that the earth's sensitivity lies around 3.3 degrees C, discussion about that figure is far from over. That's the figure the Hansen camp prefers at the moment. (And Hansen's estimates have been climbing down since 1988.)

by Nomad on Sun Feb 6th, 2011 at 10:15:35 AM EST
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It's an interesting thing to look back on predictions from climatological history... but it's barely relevant to predicting the future. To grossly over-simplify : they were trying to fit observed patterns while using too few variables; so they ended up with a CO2 sensitivity that now appears excessive.

But is it excessive, or is it being masked by other forcings? Cooling factors (particularly photochemical smog, and particles suspended in the atmosphere) are much better understood nowadays; and they are short-term phenomena. When China and India clean up their industry (and they will, and sooner than we expect), the cooling effect will greatly diminish; the particles will precipitate out of the atmosphere, but the CO2 will still be there. And the net CO2 forcing will make the temperature trend much steeper.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Mon Feb 7th, 2011 at 02:38:16 AM EST
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If it isn't relevant, it begs the question why so many people, professionals in the field, still busy themselves with the topic.

It is relevant, exactly because professionals keep bringing it up, and more importantly,  because the issue on climate sensitivity has not decisively been settled (and also because scientists have staked part of their scientific career on it). Hansen's work in the late eighties is therefore essential for "proofing" ideas on climate sensitivity - it's an important test case for our ability in predicting the future.

As noted previously, Hansen considers his 1988 estimates of climate sensitivity now too large, and now puts the number for sensitivity lower. Whether he's wrong on that number now being too low, or whether it is still too high, the earth will find out as long as we don't switch to a society that is carbon neutral. In, say, 2028 it is likely we will be able to say something useful whether his 3.3 degrees estimate comes closer to describing reality.

The political problem of course is our political strategies for adaptation should be based on that sensitivity number.

by Nomad on Mon Feb 7th, 2011 at 10:32:18 AM EST
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The political problem of course is our political strategies for adaptation should be based on that sensitivity number.

But in the case of severe negative consequences and some uncertainty about the number, should we not proceed on the basis of a somewhat worse case number? Else we are taking the position: "We can't know for sure until it is too late, so we shouldn't do anything because we might be doing the wrong thing."

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Mon Feb 7th, 2011 at 12:17:32 PM EST
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I try to be philosophically about it. Doing nothing is an ultimate position - though it is not a position I personally take. However, also doing something is politically and economically motivated, and doing something comes in gradations of how much we should do.

I was talking about adaptation in my previous post. Doing something also includes mitigation - adaptation is not the same. Even when we skip adaptation altogether, we can always do mitigation - although we're mostly choosing not to. Yet: even for mitigation the question ultimately spirals into a debate on how much mitigation over what period of time is wise. And also that is tied to climate sensitivity.

by Nomad on Mon Feb 7th, 2011 at 02:56:52 PM EST
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to one magical number : CO2 sensitivity.

We know it's not that simple. Allowing the discussion to be framed around it : "Hansen's CO2 sensitivity from 1988 is wrong, so the world is not warming all that fast" is a huge mistake.

CO2 is the biggest forcing, but a number of others, both positive and negative, are of the same order of magnitude. As a first approximation, the other forcings more or less cancel each other out, leaving a net forcing roughly equivalent to that of CO2. This does NOT mean that we can disregard other forcings!

In particular, the photochemical and particulate coolings are tied to levels of dirty industrial activity, and have varied a great deal in the past few decades. In my modest opinion, their decline in the 80s and 90s (cleanup of OECD heavy industry, decline of ex-Soviet bloc industry) steepened the global warming curve over that period; this decline has since been swamped by the dirty industry of China, India, et al, which is currently flattening the curve.

If one can't abstract that sort of influence (and especially if one declines to try), I find the idea of deriving a CO2 sensitivity from observed temperatures to be downright silly.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Mon Feb 7th, 2011 at 12:41:54 PM EST
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We know that our way of living introduces increased green house forcings to our planetary system. Uncertain is: "How much will that warming be?" And this is an essential question for policy-makers (who don't like uncertainties), and it is directly tied to this one number, whether we like it or not.

Models and measurements are the only two methodologies climate scientists have got for understanding the earth's sensitivity. And it is so focused on CO2 since other forcings are converted to CO2 equivalents. There is nothing dangerous to this choice, it is one of practicality - for as far I understand the matter. Understanding the sensitivity for CO2, should enable correlation to other forcings and reach a total sensitivity for the earth. It is true that the role of particulates, soot, clouds may play a significant influence, and they too remain relatively large unknowns. Perhaps a correlation to atmospheric temperatures may turn out to be a foolish exercise altogether, and are we better off with oceanic warming. I can't say. This is why this topic is such a battleground.

Even when sensitivity calculations are fraught with uncertainties, this does not reduce the importance of understanding CO2 sensitivity - because it largely determines the severity and rate of anthropogenic climate change, and hence its understanding underpins political solutions in response to a warming planet.

On the focus on CO2, we are in agreement. I've long argued at ET that CO2 as the main greenhouse bogeyman is a too narrowed and too limited approach of the issue at stake. As there are plenty articles in the science literature mapping out other important forcings and influences, this implies that our approach to anthropogenic climate change should also be multifaceted, and not strictly limited to the mitigation of greenhouse gases.

A positive corollary of this is that our world's fate is not decided purely by rising atmospheric CO2 concentration. Neither should it trivialize the role it does play.

by Nomad on Mon Feb 7th, 2011 at 05:33:45 PM EST
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I find the Lyman et al (2010) paper eurogreen cited and the included graph shown below to be particularly concerning. If this is a reasonable sample of the top 700 meters of the ocean it would seem something is likely happening. After all, the oceans are the biggest source of thermal inertia in the entire weather system and more ocean heat leads to greater energy in the atmospheric system. Is there any basis for making an argument that this sort of change is cyclical over a few decades or less?

And what about the rate of loss of Arctic sea ice:

From the discussion at the first link:

In this case, the match is not very good, and possibly getting worse, but unfortunately it appears that the models are not sensitive enough.

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Mon Feb 7th, 2011 at 05:51:48 PM EST
[ Parent ]
Gavin's proclamation that the earth's sensitivity lies around 3.3 degrees C, discussion about that figure is far from over.

Err, no ... what he actually wrote was (reply to comment #1 at link to RealClimate):

We can even go one step further - what climate sensitivity would have given a perfect forecast given the actual (as opposed to projected) forcings? The answer is 3.3 deg C for a doubling of CO2.

So the 3.3 deg C is a retrospective determination of the value that would have (does) give the best agreement between the 1988 model and the current observations. As such, discussion about that precise figure is over. It is a cold, hard mathematical fact (unless he made an error in running the calculation). Even future measurements do not change this value, because it is specifically an evaluation of an old model against the data available as of early 2011.

A more appropriate comment regarding current opinion on the value for climate sensitivity is in the body of the post:

... and the old GISS model had a climate sensitivity that was a little higher (4.2ºC for a doubling of CO2) than the best estimate (~3ºC).

"best estimate" and "~" acknowledge uncertainty and do not indicate a belief that discussion is over.

by det on Tue Feb 8th, 2011 at 03:42:16 AM EST
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What is visible in the graphs are trendlines, which are converted into CO2 sensitivity by a calculation that is not motivated.

The big hangup about climate sensitivity has never been much about the  sensitivity of purely CO2 - which is something that can be calculated and measured in lab conditions (it's about 1 degree for doubled CO2). The issue always has been about the effects of feedbacks, positive and negative, to increasing atmospheric CO2, in addition to the higher forcing of increased CO2.

Hansen, and Schmidt, assign certain weights to certain forcings based on certain estimates and certain model runs to explain the observed trendline, thereby finding a certain sensitivity.

There's mathematics involved, but it is far from being all hard.

by Nomad on Tue Feb 8th, 2011 at 01:53:28 PM EST
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RealClimate posted an update on that original model-data comparison: 2010 updates to model-data comparisons
by det on Sun Feb 6th, 2011 at 07:10:05 AM EST
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