Need proof of Global Warming

[brazil84]

[QUOTE=jshore]
And, I think physics gives one a good background to wade into the climate science field
[/quote]

I suspect that everyone who feels strongly enough about CAGW to debate it has the feeling that their own background is a good one to wade into climate science.

That said, I would speculate that a good background is one that gives you some familiarity with modeling; forecasting; and dealing with uncertainty (statistics, industrial engineering, economics).

For the most stringent limit on CO2 that they consider (leveling it off somewhere in the range of 450-500ppm, I think), the estimates are a reduction in world GDP growth of at most 0.12% per year over the next 50 years.

With the right background, you would have been instantly suspicious of an estimate like this. You would have looked up the details in the IPCC report, and seen that it was highly suspect, to put it nicely.

Perhaps a good background for wading into climate science is experience in having people try to deceive you. e.g. lawyer, policeman, or collections agent.

[jshore]

[QUOTE=brazil84]

With the right background, you would have been instantly suspicious of an estimate like this. You would have looked up the details in the IPCC report, and seen that it was highly suspect, to put it nicely.

[/QUOTE]

By all means, elaborate for us.

[jshore]

[QUOTE=brazil84]
First things first:

How would those scientists explain the fact that global temperatures and conditions on Earth have bounced around in a range that’s not outrageously wide? Doesn’t this suggest that there exist strong negative feedbacks in the system?
[/QUOTE]

No. First of all, what does “not outrageously wide” mean? And, what were the changes in forcings?

[Der_Trihs]

[QUOTE=brazil84]
First things first:

How would those scientists explain the fact that global temperatures and conditions on Earth have bounced around in a range that’s not outrageously wide? Doesn’t this suggest that there exist strong negative feedbacks in the system?
[/QUOTE]
It HAS bounced around a wide range; it just tends to reach a metastable state, and stay there until something pushes it into a new state. Such as, for example, pumping enough CO2 into the air to overwhelm that negative feedback. Warm up the planet enough, and it’ll likely enter a new, warmer metastable state; a warmer climate that could last indefinitely, and be at least as hard to change as our present climate has been.

[jshore]

[QUOTE=brazil84]
Here’s a video you might find interesting:

Climate Change - Is CO2 the cause? - Pt 1 of 4

[/QUOTE]

Oh please. For a discussion of Bob Carter’s talk, see my post #55 in this thread.

[brazil84]

[QUOTE=jshore]
Oh please. For a discussion of Bob Carter’s talk, see my post #55 in this thread.
[/QUOTE]

Do you seriously dispute the bounds that Carter put on past global temperatures? Because if not, your point is irrelevant.

[brazil84]

[QUOTE=Der Trihs]
It HAS bounced around a wide range; it just tends to reach a metastable state, and stay there until something pushes it into a new state.
[/quote]

I’m skeptical. What evidence do you have to support this claim?

And by the way, it doesn’t necessarily contradict my argument that there likely exist strong negative feedbacks.

[brazil84]

[QUOTE=jshore]
By all means, elaborate for us.
[/QUOTE]

The red flag is that one could know such a number down to 100th of a percent.

Then when you actually look at the WGIII report, what do you see? Well, this for starters:

It is important to note that for the following reported cost
estimates, the vast majority of the models assume transparent
markets, no transaction costs, and thus perfect implementation
of policy measures throughout the 21st century, leading to
the universal adoption of cost-effective mitigation measures,
such as carbon taxes or universal cap and trade programmes.
These assumptions generally result in equal carbon prices
across all regions and countries equivalent to global, least-cost
estimates. Relaxation of these modelling assumptions, alone
or in combination (e.g. mitigation-only in Annex I countries,
no emissions trading, or CO2-only mitigation), will lead to an
appreciable increase in all cost categories.

And another caveat:

however the number of studies are relatively limited and in
these scenarios stabilization is achieved predominantly from low
baselines.

Not only that, but you will note that the IPCC calculation apparently doesn’t make use of error or uncertainty ranges from it’s (cherry-picked) set of papers. Instead, it looks as though the IPCC just took the study with the highest estimate and used that as a maximum. I’m not an expert on meta-analysis, but that seems very sketchy to me. If you want to combine 5 or 6 studies which estimate a quantity; and each study has its own error range, I don’t see how its kosher to simply ignore the error ranges and construct a new range from the highest estimate study to the lowest estimate study.

Anyway, these are the serious problems that can be seen just from a quick perusal of the IPCC report. Any one of them calls this 0.12 figure into serious question. And I bet if you looked further under the rock, you’d find a lot more worms.

[jshore]

[QUOTE=brazil84]
The red flag is that one could know such a number down to 100th of a percent.
[/quote]

This statement reflects some mathematical confusion on your part. Let me give you an example to help explain. Say that the government proposed raising the fee to enter National Parks and estimated that this would bring in $120 million in revenues. Someone could then challenge this number by saying, “But that is 0.005% of the total government revenues (~$2.5 trillion). How could you possibly know that number down to an accuracy of 1000th of a percent?”

The correct way to look at this is that they have given a number to two significant figures and, since the first digit is a “1”, it is barely to more than one significant figure. It is reasonable not to give it to any more accuracy than that because there are indeed some uncertainties involved.

Then when you actually look at the WGIII report, what do you see? Well, this for starters:

Yes, there are uncertainties in the calculations…but where do you get this quotation from so that we can see what other parts you might have left out? Looking at the Summary for Policymakers for the WG-III report, I find the following quote:

Studies on mitigation portfolios and macro-economic costs assessed in this report are based on top-down modelling. Most models use a global least cost approach to mitigation portfolios and with universal emissions trading, assuming transparent markets, no transaction cost, and thus perfect implementation of mitigation measures throughout the 21st century. Costs are given for a
specific point in time.

Global modelled costs will increase if some regions, sectors (e.g. land-use), options or gases are excluded. Global modelled costs will decrease with lower baselines, use of revenues from carbon taxes and auctioned permits, and if induced technological learning is included. These models do not consider climate benefits and generally also co-benefits of mitigation measures, or equity issues.

Note that this says some of the same things as yours does but also includes uncertainties / assumptions that go the other way (which makes me wonder if you “cherry-picked” which uncertainties/assumptions you quoted in the quotations that you gave).

In addition to the ones that obviously go the other way, it is worth noting, as is stated very clearly in the Third Assessment Report, that the “top down modeling” that they employ here generally gets a higher cost number than is obtained by “bottom-up modeling”. Part of the reason for this is that the top down approach generally assumes that you start off at an optimal point where there are no zero- or negative-cost solutions, in contrast to what is found in the real world, e.g., by BP when they made a Kyoto-size cut their emissions and ended up saving money:

When Browne [CEO of BP] stood up at Stanford this past spring, he was there to report hard numbers: BP had not just met its target – to reduce its emissions of greenhouse gases by 10 percent below 1990 levels – it had exceeded it, done so eight years ahead of schedule and with no net economic cost. In fact, because of energy efficiency measures, the emissions reductions amounted to a net gain of $600 million. ‘‘And we are not,’’ he told me later, ‘‘an inefficient company.’’

BP’s achievement complicates matters for Bush, who has pronounced the Kyoto Protocol ‘‘fatally flawed’’ because regulating carbon-dioxide emissions ‘‘does not make economic sense for America.’’

That line of argument does not persuade Browne. ‘‘If you say to people, ‘Do you want to develop the world and have a good living standard, or do you want a safer environment?’ people are terrified by the choice,’’ Browne said to me last spring. ‘‘That is a failure of leadership.’’ Speaking of leadership, I asked, what did he think about Bush’s position on the issue – that caps on emissions would be too costly for American businesses? Browne paused, then answered, careful not to mention any names in particular: ‘‘Well, it’s unfair to the world to say that none of this is possible when it is.’’

(The IPCC report does say “Bottom-up and top-down models have become more similar since the TAR as top-down models have incorporated more technological mitigation options and bottom-up models have incorporated more macroeconomic and market feedbacks as well as adopting barrier analysis into their model structures” so the difference is apparently not as great as it used to be.)

@brazil84

Not only that, but you will note that the IPCC calculation apparently doesn’t make use of error or uncertainty ranges from it’s (cherry-picked) set of papers.

Since you claim that the papers are “cherry-picked”, could you let us know some that you left out?

Anyway, these are the serious problems that can be seen just from a quick perusal of the IPCC report. Any one of them calls this 0.12 figure into serious question. And I bet if you looked further under the rock, you’d find a lot more worms.

Again, I know that there are considerable uncertainties and assumptions in economic estimates of this sort. However, as I noted in a previous post, the historical record shows that in the past even the cost estimates of the regulating agency (such as the EPA) has tended to be an overestimate of the actual costs for environmental regulations. Needless to say, the counterestimates of the industries being regulated have tended to be even more out-to-lunch.

[jshore]

intention: Thanks for your responses.

[QUOTE=intention]

If you think that claiming you can predict the climate 100 years from now is not an extraordinary claim, I’d hate to see what you think is an extraordinary claim.
[/quote]

Well, the point is that over a long-term, the climate under a significant forcing is expected to be dominated by the magnitude of the forcing and the sensitivity of the response to the forcing. While we don’t know either of these to extreme accuracy, we do know both of them with enough accuracy to make projections, albeit ones with still fairly large error bars. And, of course, there is always the danger in a complex nonlinear system that we could pass a tipping point and have something much more dramatic happen…so that is a sense in which the IPCC projections could actually turn out to be too conservative.

I suppose if I were talking about the Santer paper, your statement would make some sense … I thought you had been following the literature, my bad.

Well, your statement sounded almost word-for-word like how you had summarized the Santer paper in the past. What paper(s) are you referring to now?

Oh, I see, you don’t answer the question, you attack me instead … well, this fighting ignorance is a risky job, I guess I just have to toughen up.

Yes, I think you should toughen up. If you are going to viciously attack highly respected scientists on the basis of your interpretation of what they say…and to demand a very high standard with respect to being honest and not exaggerating, then you should expect to be held to that standard yourself, should you not? People rightfully tend to hold such people to high standards…Just look what happened to Elliott Spitzer; a lot of people have noted that someone who had not been so exacting on other people would have been able to weather such a scandal but for Spitzer his whole ethos was built on demanding such high standards from other people.

And, in your case, there is an additional reason to demand a high standard from you and that is because your whole case here rests very strongly on your own credibility because you are saying things that are completely at odds with what is being said by scientific organizations that have a very strong reputation for being very credible.

I have no antipathy to scary scenarios. I have an antipathy to untrue scenarios.

Well, that’s great but then how do you decide what is a true scenario and what is an untrue scenario? You seem to have decided that your scenario is a true one and yet you have yet to cite any reputable studies to back it up as even a possible scenario, let alone any sort of likely one.

In case you forgot, it was, is a scientist who is balancing honesty and effectiveness being “measured and careful”? … but I digress.

The answer that I would give is NO if they are really trading off honesty in trying to be more effective. However, if you have only 50 words to explain something that actually would take several thousand words at least to explain something, you clearly do have to make some choices in regards to what you say and what you leave out. One should do that in a way that is not dishonest but I hope you can at least understand the pressure that puts one under. Look, how about this: Why don’t you try to summarize your position on climate change in 50 words and then we can debate how effectively you have balanced honesty and effectiveness in making your case?

To date, we haven’t come up with a plan to significantly cut emissions which does not require huge, unimaginable expenditures of money. Kyoto has already cost hundreds of billions. Not only has Kyoto not made a significant cut in the emissions, it has made no cut at all. The goal was for emissions to be cut to 1990 levels, but instead of being cut, emissions increased. Not a success in any sense, emissions went up instead of down … so we have to assume that a successful plan to cut emissions will cost even more.

Where do you get your estimates for what Kyoto has cost? Was Kyoto ever meant to already result in a cut in worldwide emissions or was it meant to start on the path toward stabilizing emissions and toward pushing the market to develop the technologies to reduce emissions? Was this all supposed to happen overnight?

As always, the poor will be hit by this the hardest. If you have a preferred term for the world’s poor people taking it up the as* once again, other than “impoverishing the world”, I’m happy to use it.

Well, it is an unfortunate fact that the poor bear the brunt of most things…including the likely effects of climate change, which is why most poor nations have supported the Kyoto and larger UNFCCC (United Nations Framework Convention on Climate Change) process. At any rate, one of the reasons why Kyoto did not put any emissions restrictions on the developing countries was in order to try to avoid putting costs on countries that are not in a good position to afford it (and, frankly, generally don’t have the technological advancement to come up with the needed technologies anyway). Yet, many people who oppose action on climate change complain bitterly about this. It seems to me that people who oppose action on climate change will never be happy and are more than happy to embrace both arguments based on how much it will hurt poor people and how it is all a socialist plot to redistribute money from the wealthy nations to the poor ones.

But if you wish, we could call it something like the “anti-Robin Hood syndrome”, rob from the poor to give to the rich, is that less scary?

Well, like I pointed out above, could those of you opposing action to mitigate climate change decide whether it is an anti-Robin Hood idea or whether it is a socialist idea foisted on the United States by the poor countries to try to steal our wealth because, frankly, I am getting tired having to argue against both complaints.

But the onus is not on me to provide the numbers. You want us as a society to spend billions of dollars on something, it’s your responsibility to put a price tag on it. If you have an inexpensive way to “significantly” cut emissions, I’m all ears … but somehow, you’ve never revealed that plan to us.

No, the onus is on you to explain why you have the right to put stuff into the atmosphere, which you don’t own, that is affecting everyone else and not pay the costs associated with this.

It can’t be a plan involving just one country, however. No matter what a single country does (within the range of real possibilities), it cannot “significantly” cut world CO2 emissions. Unless India and China and the entire developing world sign on to the plan, the cuts will not be significant, and the effects will hit hardest on the poor.

I agree that eventually China and India have to be a part of it…and they accept that too. However, for the reasons you note regarding the poor tending to bear the brunt of any costs of any sort (and, also, out of basic considerations of fairness regarding who has been responsible for most of the increase in CO2 levels in the atmosphere and practicality regarding who has the technological capabilities to best develop the new technologies), I think it is reasonable for the developed countries to go first. (Although I believe Kyoto also has some flexibility whereby the developed countries can earn some credits by supporting emission-reducing projects in developing countries, which is also a good idea.)

I agree with you that the process is not an easy one. This is certainly one of the largest collective challenges that human society has faced and it is a large problem that cannot be solved all at once. It will be an on-going process. However, getting off fossil fuels is something that will have to be done eventually anyway, as their supplies are limited. So, the real question is do we start the process now so that it can be done gradually and soon enough that we do not dump the entire store of carbon built up over hundreds of millions of years into the atmosphere within a few centuries or do we just sit back and wait, only going through the process after we have done what may be considerable irreversible damage to our environment, both through altering the climate and acidifying the oceans (and, frankly, perhaps causing other problems that we haven’t even anticipated)?

[brazil84]

[QUOTE=jshore]
This statement reflects some mathematical confusion on your part.
[/quote]

Oh really? Well let’s extend your example a bit. Suppose somebody told you that raising the fee to enter national parks would increase government revenue by 0.0048% over the next 50 years. Would you be impressed by that estimate? Of course not. Because factoring in future government revenue adds in a whole new area of uncertainty.

The fact is that we don’t know what government revenue will be 5 years from now, let alone 10 years from now. Not down to the nearest hundred million dollars, anyway.

Yes, there are uncertainties in the calculations…but where do you get this quotation from so that we can see what other parts you might have left out?

Lol. It’s right there in WG III, Chapter 3.

Looking at the Summary for Policymakers

Ahhhh . . . I just thought of another education background that would be useful in the global warming controversy: Accounting. When you read the IPCC report, it’s like studying the financial statements of a company that might be the next Enron. In other words, you can’t just look at the summaries and read what the company wants you to read. You have to study the footnotes too.

And if there are assumptions that “go the other way” as you say, it only adds to the uncertainty, making the 0.12 percent figure even less credible. Because errors don’t necessarily cancel out.

Since you claim that the papers are “cherry-picked”, could you let us know some that you left out?

It says right in the report that they selected papers on a case by case basis.

[jshore]

[QUOTE=brazil84]
Oh really? Well let’s extend your example a bit. Suppose somebody told you that raising the fee to enter national parks would increase government revenue by 0.0048% over the next 50 years. Would you be impressed by that estimate? Of course not. Because factoring in future government revenue adds in a whole new area of uncertainty.

The fact is that we don’t know what government revenue will be 5 years from now, let alone 10 years from now. Not down to the nearest hundred million dollars, anyway.
[/quote]

But, that is irrelevant to knowing approximately how much difference this particular cost will make. In your example, I don’t see anything wrong with saying that it will increase government revenue by that amount. Now, if you were to use that to conclude that government revenue would be exactly $5.025743 trillion dollars in 50 years, then yes, I would say that this is too many significant figures to carry. However, it doesn’t stop us from having a reasonable estimate of the difference in revenues between what would be obtained with the current fees and with the new fees.

And if there are assumptions that “go the other way” as you say, it only adds to the uncertainty, making the 0.12 percent figure even less credible. Because errors don’t necessarily cancel out.

The point is that the effects would go in the opposite direction. I’m not saying they exactly cancel…but they should at least partially do so. And, yes, the 0.12 percent figure is an estimate…It is not an exact number.

It says right in the report that they selected papers on a case by case basis.

You claimed that they “cherry-picked” the papers, implying that they left some out and, in particular, I assume your implication is that they left out ones with higher estimates. However, here is the full quotation from Chapter 3 of the WG-III report where they use the phrase “case-by-case basis”:

The grey shaded area in Figure 3.25 illustrates the 10th–90th percentile of the mitigation cost ranges of recent studies, including the TAR. The area includes only those recent scenarios in the literature that report cost estimates based on a comprehensive mitigation analysis, defined as those that have a sufficiently wide portfolio of mitigation measures. The selection was made on a case-by-case basis for each scenario considered in this assessment. The Figure also shows results from selected illustrative studies (coloured lines). These studies report costs for a range of stabilization targets and are representative of the overall cost dynamics of the full set of scenarios. They show cases with high-, intermediate- and low-cost estimates (sometimes exceeding the 80th (i.e. 10th–90th) percentile range on the upper and lower boundaries of the greyshaded area). The colour coding is used to distinguish between individual mitigation studies that are based on similar baseline assumptions.

So, as I understand it, what they are saying is that for each of the different scenarios (i.e., levels of stabilization), they looked to see which one satisfied the criteria of presenting a comprehensive mitigation analysis. So, it is not saying that they “cherry-picked” them; the “case-by_case” part just refers to the fact that for each scenario, they looked to see which of the studies did a comprehensive mitigation analysis for that particular scenario and included the result of the study for that scenario if it did so. Then, to produce the figure, they plotted both the gray band representing the 10-90% results and then also plotted a few representative results that spanned the range from high- to low-estimates.

[brazil84]

[QUOTE=jshore]
But, that is irrelevant to knowing approximately how much difference this particular cost will make.
[/quote]

Of course it’s relevant. If you are describing cost as a percentage of GDP, then any uncertainty – whether in the numerator or denominator – will be transmitted to your final figure.

I don’t know how to make this any clearer.

The point is that the effects would go in the opposite direction. I’m not saying they exactly cancel…but they should at least partially do so.

So what? It won’t cancel out the uncertainty. Even partially.

And, yes, the 0.12 percent figure is an estimate…It is not an exact number.

Sure, and the IPCC has put lipstick on the pig by offering a number that seems like a precise estimate – but essentially amounts to a wild-ass guess.

You claimed that they “cherry-picked” the papers, implying that they left some out

That’s right, and I admit that my assumption is based on the IPCC’s lack of credibility combined with the fact that they gave themselves discretion to pick and choose.

And I’m pretty confident that if I had the time, I could find papers that give bigger estimates which the IPCC left out. Just like they left out Lindzen’s paper on sensitivity estimates.

However, for the sake of argument let’s assume that the IPCC didn’t cherry pick. It still doesn’t change my conclusion that the 0.12 estimate is highly suspect – to put things nicely.

[jshore]

[QUOTE=brazil84]
Of course it’s relevant. If you are describing cost as a percentage of GDP, then any uncertainty – whether in the numerator or denominator – will be transmitted to your final figure.

I don’t know how to make this any clearer.
[/quote]

You can’t make it clearer because you don’t know what you are talking about. Say that the GDP is only known to 10%, then this would introduce a 10% uncertainty in the denominator so that the 0.12% would really be between 0.108% and 0.132%.

Look, the point is that you are simply wrong to be saying, “The red flag is that one could know such a number down to 100th of a percent.” The fact is that the IPCC gave a figure to two significant figures…and barely that since the first digit is a 1. You may not understand this, but I trust that the other people reading this thread understand.

Sure, and the IPCC has put lipstick on the pig by offering a number that seems like a precise estimate – but essentially amounts to a wild-ass guess.

They never claimed it was a precise value…but neither is it a “wild-ass guess”.

That’s right, and I admit that my assumption is based on the IPCC’s lack of credibility combined with the fact that they gave themselves discretion to pick and choose.

The IPCC enjoys great credibility with most of the nations of the world, including the U.S. government, and the scientific community in the world. The fact that it doesn’t have much credibility with you perhaps says more about you than them.

And I’m pretty confident that if I had the time, I could find papers that give bigger estimates which the IPCC left out. Just like they left out Lindzen’s paper on sensitivity estimates.

They didn’t leave out Lindzen’s paper; they discussed it. And, what they focussed on were papers that actually with some attempt at rigor derived a probability distribution for the sensitivity (e.g., using Bayesian methods). Lindzen’s paper, in addition to its many other faults, didn’t do that…but just made some vague conclusions that results seemed to fit best with a sensitivity under 1 C.

However, for the sake of argument let’s assume that the IPCC didn’t cherry pick. It still doesn’t change my conclusion that the 0.12 estimate is highly suspect – to put things nicely.

Well, the “less than 0.12% of GDP growth per year” is the best estimate that we have. And, as I have noted before, the history of these estimates for the costs of environmental regulation is that they have in the past been too high because they have failed to take into account the market’s ability to find the least-cost solution (and have failed to account for the non-optimality of the initial state and so forth). These economic models are apparently improving, so maybe their overestimation of the costs is not so much of an issue anymore, I don’t know.

[brazil84]

[QUOTE=jshore]
Say that the GDP is only known to 10%, then this would introduce a 10% uncertainty in the denominator so that the 0.12% would really be between 0.108% and 0.132%.
[/quote]

Right. As I’ve said repeatedly, uncertainty about GDP is transmitted to uncertainty about the estimate. This is very basic mathematics here.

That’s why the figure is suspect on its face. We can’t know next year’s GDP growth to one hundredth of a percent. So how can we know the effect of mitigation on GDP to one hundredth of a percent?

Now, I realize that there is an explanation for this – that the 50-year estimate is something like 5.5 percent of total GDP, and that equates to .12 percent per year different. But that only implies another question: How can we know that the cost of that level of CO2 mitigation, in 50 years, will be 5.5% of GDP in 50 years? The 5.5% figure is ridiculous on its face. There’s no way we could know the figure that precisely.

One would hope that the study in question gave a range for its estimate, but the IPCC simply ignored that range, if it ever existed. A point that you haven’t even bothered to deny. And this is an organization that has great credibility? Give me a break.

They never claimed it was a precise value

Of course not. They simply implied it, without actually claiming it. A classic alarmist ploy.

The fact that it doesn’t have much credibility with you perhaps says more about you than them.

It says something about everyone, actually.

They didn’t leave out Lindzen’s paper; they discussed it.

Whatever. They omitted it from their chart. As I recall, they never explained what the inclusion criteria were. Your explanation is just speculation.

Well, the “less than 0.12% of GDP growth per year” is the best estimate that we have.

So what? If it’s a lousy estimate, it’s a lousy estimate. I bet if you took the study its based on, and did a simple range sensitivity analsys, you’d end up with a huge honking range.

[intention]

jshore, you say:

The fact is that the IPCC gave a figure to two significant figures…and barely that since the first digit is a 1. You may not understand this, but I trust that the other people reading this thread understand.

I don’t have a dog in this fight, I’m not taking sides on the underlying question.

But two significant figures is two significant figures, whether the first digit is a 1 or a 9 … so I fear I don’t understand this. What difference does it make what the amount of the significant digit is, whether it is 1, 9, or 5. Is a 9 somehow more significant than a 1?

w.

[intention]

tim314 (tim pi?), you finished an interesting post up above with:

[QUOTE=tim 314]
Then, like I said, it becomes a question of how much warming is expected due to the greenhouse effect. But if we can’t agree that the greenhouse effect exists and thus that CO2 causes warming, then this whole discussion is a waste of time.
[/QUOTE]
You are correct to focus on the basics. The greenhouse effect exists. No question. CO2 changes cause a change in radiative “greenhouse” forcing. No question.

How much warming will result from that forcing? Unknown at this time. This number is known as the “climate sensitivity”. It is measured either as the amount of warming from the change in forcing from a doubling of CO2 (°C/doubling), or alternatively in °C per 1 W/m2. I prefer the latter measurement, because the change in forcing from a doubling of CO2 has a range of definitions from about 3.6 to 4.1 W/m2, making it uncertain.

Scientific estimates of climate sensitivity range from near zero to around 2°C per W/m2. The IPCC considers the range to be 0.4 to 1.2, with a most probable value around 0.8. If it is 2, then there will be climate catastrophe, a 7.4°C swing.

My own estimate of the climate sensitivity is about zero. Let me try to explain why.

Most people have an image of the climate as being in some kind of delicate and precise balance. In this view, a slight adjustment of one of the variables (say CO2 or solar input) causes a corresponding change in equilibrium temperature.

In fact, the climate is a huge natural heat engine. The heat comes in at the tropics. Some of that heat is transported by the ocean and the atmosphere to the cold end of the heat engine, doing work along the way. How much heat is transported?

Suppose we take a one million watt (one megawatt) power plant for comparison. It will run a small town. So let’s scale up, a one thousand megawatt plant. Eight of these giants will run New York City. Suppose we start placing them on the equator, to represent the heat carried away from the equator by natural circulation. How many of these huge thousand megawatt power plants will it take to equal the heat circulated in the climate heat engine?

The answer is, we’d have to place one of these giant power plants every twenty feet (six metres) all the way around the world to equal the natural heat circulation. It would take over seven million of these to generate the same amount of energy that is constantly being circulated polewards by the ocean and the atmosphere.

Flow systems such as the climate are governed by the Constructal Law (see Bejan . This states that the climate system self-organizes in such a manner as to maximize power created and dissipated in the heat engine. Bejan has shown that we can derive the size and flow of the Hadley cell circulation from the Constructal Law.

This means that the earth has an equilibrium state, which is that state where the most power is dissipated in the circulation of the ocean and the atmosphere from the tropics poleward and back again. It is not at some hypothetical delicate balance, easily moved by a small forcing. It is at a constantly maintained equilibrium state of maximum power dissipation, in a huge, colossal heat engine moving unimaginable amounts of energy.

The parameters of this equilibrium climate state are set by the locations of the continents and the unchanging physics of wind and water — the rate of cloud formation, the amount of energy transported at a certain speed compared to the turbulent power dissipation at that speed, the relative weights of air (28.8) and water vapor (18), the Clausius-Clapeyron evaporation equation, and the like.

As observational evidence for this equilibrium state, consider that over the last half billion years, the strength of the sun has increased by about 17 W/m2. If the IPCC central forcing estimate is correct and the sensitivity is about 1°/W-m2, the earth should have warmed by 17°C … but that didn’t happen.

In fact, the Earth has seen an ever-warming sun, a number of asteroid strikes, massive volcanism, shifting continents, and a host of other huge changes … but the climate has merrily gone along at about 290°K ±2% for half a billion years, and ±1% for much of that time.

That’s why I say that the climate sensitivity is effectively zero. Not because there is no change in forcing. But because the equilibrium state of the planet is determined by maximum power production/dissipation, not by the forcings. If the climate didn’t change from a huge change in the solar “constant” over the millennia, why should a much smaller change in CO2 forcing cause a large perturbation?

Further information on this concept is available here, peer reviewed so you don’t think this is just my idea.

w.

[jshore]

intention, your most recent post contains some very interesting food for thought. Indeed, there are some interesting questions about how the earth’s climate has been regulated within a certain general range throughout its entire history. Unfortunately, I worry that your hypothesis may in some sense explain too much…and, in particular, that it may explain periods far back in time for which the actual conditions (in terms of climate, atmospheric composition, continental and ocean geology) are poorly constrained by the more limited experimental evidence at the expense of our understanding of more recent periods for which we have considerably more detailed information.

In particular, I was wondering how this theory is compatible with the fairly dramatic swings in climate that we have seen, e.g., during the current period of glacial – interglacial oscillations over the last couple million years (with the most recent swing being only about 10,000 years ago or so) in response to what seem to be fairly small changes in forcing. Secondly, I will point out that if you look at this Wikipedia page, they discuss the current thinking on the faint-young-sun paradox. Indeed, they do propose that there are some negative feedbacks to account for this; unfortunately, however, the evidence suggests that the negative feedbacks involve greenhouse gases such as CO2 and methane and operate on considerably longer geologic timescales than the one that is of interest to us with the current accumulation of CO2 in the atmosphere. Here is an extensive quote from that page about this:

The tension between the two hypotheses stems from the incorrect assumption that atmospheric gas concentrations in the past were the same as today. First, before the advent of abundant life the atmospheric oxygen concentrations were orders of magnitude lower than today. In the presence of oxygen methane breaks down to carbon dioxide, so in the absence of oxygen the methane concentration could be much larger than currently observed. Methane is a more potent greenhouse gas than carbon dioxide, so the relative abundance of atmospheric methane throughout Earth’s history must be considered when modeling the temperature.

Further, the inorganic version of the carbon cycle can be expected to provide negative feedback towards an Earth with liquid water. Carbon dissolved in liquid water can form carbonic acids, which can then interact with calcium to produce calcium carbonate. If rainfall were to cease and the oceans froze over, then this part of the inorganic carbon cycle would shut down. Periodic explosions from volcanoes would then cause a net increase in the atmospheric carbon dioxide and methane levels with no liquid water to absorb these emitted gases. Eventually the concentrations would become large enough that the surface temperature would rise due to the greenhouse effect. When the surface temperature became large enough for the oceans to melt and rainfall to resume the other half of the inorganic carbon cycle would turn on and moderate the greenhouse gas concentrations.

Another question that I had is whether the hypothesis that you present is compatible with the known effects of greenhouse gases in warming the planet. I.e., it is a simple radiation calculation to determine that the earth’s surface is some 33 C warmer than it would be with its current albedo in the absence of greenhouse gases. So, it is clear that greenhouse gases have a significant effect on climate, although it is admittedly unclear to me what numerical constraints this would actually put on climate sensitivity.

So, in summary, as we currently understand more recent paleoclimate events, it seems that the earth’s climate is actually quite sensitive to changes in forcing. When we look on the much larger timescales that you noted, there is evidence that negative feedbacks seem to come into play; however, the experimental evidence during these time periods is considerably more limited and, from what we do know, it seems that the negative feedbacks are likely to involve greenhouse gases in a way that only operates on timescales that are much longer than the current timescale of interest.

[intention]

jshore, your comments as always are interesting and provocative.

I am aware of the alternative GHG hypotheses for the solution of the “Faint Early Sun” paradox, although they are given somewhat short shrift in Wikipedia. However, if we are to ascribe the additional heating to CO2/methane, several conditions have to be met:

1. The sun is thought to have warmed some 30% in the last three billion years or so. This is a change of about 80 w/m2. To counterbalance this, CO2 would have to double, not increase but double, about 80/3.7 = 21 times. Minor problem - 21 doublings of the current 380 ppmv yields an atmosphere with more than 100% CO2. This means that methane must have been involved as well … but then we have to assume two greenhouse gases in delicate balance with temperature, not just one.

2. Since the sun has warmed gradually over this period, in order for this plan to work, the CO2/methane have to very gradually decrease, from a proposed high some three billion years ago, to the present much lower state. There is no evidence that this has happened.

3. In order for this plan to work, as the temperature slowly increases, the CO2/methane levels would have to decrease. I know of no evidence, either observational or theoretical, which shows a long-term negative correlation between temperature changes and GHG changes.

4. In order for this plan to work, the CO2/methane could not decrease linearly. Since the forcing is logarithmic, this would require a very exact exponential decay of the GHGs to stay in line with the increasing forcing.

In the words of the immortal IPCC, I find it “highly unlikely” (<5% chance) that all of those conditions have obtained over the entire period of the last three billion years.

This question, of whether the world has an equilibrium temperature, is to my mind the great unanswered question in the field. Unfortunately, it cannot be answered with GCMs, at least in their present form. To do that, we need models like Wu’s model in my citation above.

w.

PS - I just noticed that the IPCC’s list of terms, viz:

In this Summary for Policymakers, the following terms have been used to indicate the assessed likelihood, using expert judgement, of an outcome or a result: Virtually certain > 99% probability of occurrence, Extremely likely > 95%, Very likely > 90%, Likely > 66%, More likely than not > 50%, Unlikely < 33%, Very unlikely < 10%, Extremely unlikely < 5%.

doesn’t contain any term for a couple of the slots. There’s no term “Less likely than not <50%” … hmmm. And there’s no term for “Really, really unlikely < 1%”.

Curious.

[jshore]

[QUOTE=intention]

I don’t have a dog in this fight, I’m not taking sides on the underlying question.

But two significant figures is two significant figures, whether the first digit is a 1 or a 9 … so I fear I don’t understand this. What difference does it make what the amount of the significant digit is, whether it is 1, 9, or 5. Is a 9 somehow more significant than a 1?
[/QUOTE]

Well, the rule on using significant figures is sort of fuzzy, but as I understand it, it argues roughly that the number of significant figures you used should be determined by the fact that the last one you quote might be wrong…but the next digit is very likely correct…or at least wrong by at most one digit (e.g., so if you say “0.19”, the correct result could be “0.21”, say). Let’s just arbitrarily simplify this by saying that we imagine the last digit quoted can be off by at most 3. Then, “0.12” corresponds to 0.12 ± 0.03 and so it is implying knowledge to ±25% variation in the value. However, “0.92” corresponds to 0.92 ± 0.03 and thus implies knowledge to ±3% variation in the value.

That’s all I meant…namely the observation that if you have a number quoted to 2 digits and the leftmost digit is a 1, then being off by one in the right digit is an error on the order of ten percent ,whereas if you have a 2-digit number and the leftmost digit is a 9 then being off by 1 in the right digit is only an error of order one percent.