Need proof of Global Warming

[jshore]

@flex727

It does seem like a case for guaranteed loss if we take action verses potential loss if we don’t. Risks on both sides need to be weighed properly. I have never seen the proper risk/benefit analysis for both sides that I consider an absolutely necessary step in the process. Anti-CAGW folk usually minimize the potential damage that might result from climate change, though there is plenty of that info available in the MSM. Pro-CAGW folk almost never consider the significant risk and damage resulting from reduced growth and prosperity. This is perhaps more difficult to predict, but it never appears in the MSM.

The IPCC actually deals with the send thing you mention, i.e., an estimate of the reduction in growth that would occur from mitigation. 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.

The Stern Report attempted to provide estimates of costs both ways (i.e., costs of mitigation vs. costs of damage from AGW) and concluded that the latter were much higher. There have been criticisms of this report…a lot that I think are the usual suspects arguing the usual things…although there are also some concerns about it that seem to be legitimate. Clearly, arriving at these costs on both sides involves a lot of uncertainty and is sensitive to various assumptions.

An approach that I like best is that presented in this paper. It recognizes the inherent uncertainties in knowing the costs due to damages of AGW and when those costs kick in as a function of our emissions. So, it basically assumes that in 30 years, we will have a much better idea of what the climate sensitivity is to greenhouse gases and the maximum global temperature rise that keeps us below the regime where damages become very large. And, it asks what is the least-cost policy to pursue in the meantime.

Of course there is, but the complexity of interactions in the climate system is mind-boggling. My degree is in Physics, but I don’t purport to understand climate science - the people who do don’t give me a warm feeling (I’m not talking about members of this board).

My degree is in physics too. And, I think physics gives one a good background to wade into the climate science field…although clearly one has to read a lot of stuff in order to get up to speed and I am still trying to do that. I would also note that it seems to me (from an admittedly limited perusal of CVs) that many of the people working in the field seem to have physics backgrounds also and then switched toward climate science at some point after undergrad.

Not having a sufficient understanding is a GREAT argument for inaction. Our history is riddled with examples of screwed up ecosystems resulting from science meddling with things we didn’t understand but thought we did. The Cane toad is popularly known for its introduction in Australia to control beetles. They failed to do that and made a worse problem. I’ve personally seen the damage caused by the introduction of Kudzu in the southeastern US where it was introduced in an attempt to control soil erosion. These are just two that come immediately to mind, but these are such simple little systems compared to global climate, and there are so many more examples that we should be very wary when we are told that science understands this stuff.

But, it seems to me that your examples are of tampering with things in order to try to correct for a problem that we are causing…what I have sometimes called “the swallow a spider to catch the fly” approach. An analogy in climate science would be embarking on a program to inject lots of aerosols into the stratosphere to counteract the warming effects that we are causing…and I agree that such approaches are dangerous. In fact, apparently many climate scientists are beginning to understand why such solutions may not be very good. (There was a RealClimate piece reporting from a session at the AGU meeting on such geoengineering solutions.)

However, I don’t think reducing our CO2 emissions falls into this category at all. It is just reducing the perturbation that we are putting on the climate system. I suppose, depending on the solutions, you could worry about causing very different environmental problems or economic problems but I don’t really see how there is risk to causing more damage to the climate system through mitigation.

Now, why don’t I get as alarmed by the inadvertent tampering with the ecosystem that occurs with man’s CO2 production? Because there is an undeniable tremendous benefit resulting from that CO2 output. Here is my analogy: there are a small handfull (<10) of deaths each year in the US from shark attacks and yet we have beach closures and panic resulting. However, there are 40,000 deaths each year from traffic accidents. Why don’t we have a level of panic 3 orders of magnitude greater? It’s because the benefit of automobiles is much greater overall than the death toll. I have not seen evidence that the potential damage from CAGW is greater than the overall benefit mankind gets from the CO2 production.

A few comments here: Well, sure there are benefits but that doesn’t mean we should not worry about the costs. And, we also need to ask if we can have much of the benefits still without incurring the costs. And, furthermore, we already know that we can’t simply burn fossil fuels forever because they are a finite resource. So, we need to develop alternatives. Isn’t it better to put the market incentives for that to happen in place now rather than wait until we have incurred a significant amount of the costs.

I agree with you about auto accidents although I guess I am a little more skeptical than you about whether we have made the optimal decision in that regard. People have strange ways of dealing with risk and it is strange to me how risk-tolerant people are with automobiles and how risk-intolerant they are, with say, airline fatalities…And, I guess I am not willing to believe that this has all come about through people making the optimal rational choices.

Well, I certainly see exemptions in Kyoto for developing nations. Of course they don’t mind seeing our prosperity damaged as long as they are unaffected. This is clearly short-sided though as we have an interconnected global economy.

I am amused by the way you have reasoned through this. You recognize that it would be short-sighted of them to damage our prosperity for no gain but then conclude that that is their approach anyway. Perhaps they are more intelligent than you give them credit for and they recognize that damaging our prosperity is not good but think that the benefits of the emissions reductions outweigh the costs.

And, by the way, it has always been stated that Kyoto is the start of a process and although the developing nations don’t have any commitments under Kyoto, they will in the future. So, I think they understand that in agreeing to Kyoto they are starting down a road that will lead to them having to make commitments too.

Ugh, please don’t get into this. This is the kind of argument that you bring up occasionally that hurts your credibility because it makes it sound like your position is a result of your political leaning rather than your scientific understanding.

Well, everyone clearly has political leanings. However, even if we might have differences of opinion on issues regarding distribution of wealth and so forth, I think you have to admit that the problem of poverty in the world is not in large part due to there being inadequate wealth to go around. I.e., there is no evidence that if the average wealth of the world increased by a factor of 2, or a factor of 5, that would automatically translated into huge gains in wealth of those at the bottom. In fact, I think that historically the increase in wealth has occurred in large part by having the distribution broaden rather than just shift upward.

Also, measures of wealth such as GDP are imperfect indicators and, in particular, do not well-measure the effects of degradation of the environment…Effects that can, among other things, have important effects on future wealth.

Okay, it looks like I failed to keep this short as I promised. Sorry. Your response to my post helped me to think through some stuff and I got on a bit of a roll. Thanks for what you do jshore.

Thanks for the thoughtful discussion, flex727.

[intention]

jshore, as always … good to hear from you. You say:

@jshore

@intention

Now I know for certain that you have not been following climate science. While this may be true for other scientists, climate scientists go around claiming outrageous things like that they can forecast the climate 100 years from now, and that the science is settled, that we understand the climate well enough to model it … hardly “measured and careful” claims.

First of all, I would say that you are somewhat simplifying what the scientists are claiming. Second, all because you personally don’t believe the evidence is there for scientists to make a claim doesn’t mean it actually isn’t there. You don’t get to be judge and jury on whether a claim is outrageous or reasonable.

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.

@jshore

@intention

Their vaunted climate models badly miss the most crucial forecast, that of the tropical tropospheric temperature, and they want to claim that the models are correct and the data is wrong … now that’s a claim that is neither measured nor careful.

We’ve discussed the Santer et al. paper before and this description of it is, ironically, “neither measured nor careful”.

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.

@jshore

@intention

In this vein, we just discussed Stephen Schneider, who thinks that scientists have to strike a balance between honesty and effectiveness … is a scientist who is balancing honesty and effectiveness being “measured and careful”? Or is he just carefully picking which well-measured lie to tell?

Well, since you bring up Schneider again, let us talk about those without sin casting the first stone. In a post here yesterday, you said,

@intention

So although “significantly cutting emissions” makes a great sound bite, the problem is that no one has figured out how to do it without impoverishing the world.

To me, that sounds a lot like a “scary scenario” and “a simplified, dramatic statement”, but I guess you must have very firm evidence that I wasn’t aware of to support this idea that significantly cutting emissions would impoverish the world…otherwise, your antipathy toward offering up scary scenarios would have prevented you from doing it.

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.

I have no antipathy to scary scenarios. I have an antipathy to untrue scenarios. I have an antipathy to anyone who thinks scientists should balance honest and effectiveness. If an asteroid is about to hit the earth, that’s a scary scenario, and scientists would be justified in saying “An asteroid is about to hit the earth”, despite the fact that it is scary.

And I have an antipathy to people attacking me instead of answering the question, if you’d like to answer it now that would be fine. In case you forgot, it was, is a scientist who is balancing honesty and effectiveness being “measured and careful”? … but I digress.

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. 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.

See, I live in the developing world. The poorest of the poor are not just numbers to me, they are among my friends and acquaintances. For the wealthy in the developed world, wasting sums larger than my country’s GDP in unsuccessfully trying to screw around with CO2 levels is a great way to assuage their consciences. They don’t even notice what’s happening at the far end of the food chain, where their pollyanna ideas, like converting food to fuel, hit the hardest. The holier-than-thou folks in their biodiesel fueled cars are burning up some poor kid’s breakfast so they can drive to McDonalds to get their breakfast… me, I call taking food from the poor to fuel the rich “impoverishing the world” … but like I said, I’m open to suggestions. It’s not a scary scenario, it’s a scary reality. 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?

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.

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.

And call me crazy, but I’m not interested in symbolic gestures that cost billions of dollars.

So break out your plan, we’re all waiting …

w.

[tim314]

It seems to me that it’s pretty obvious that if we add enough CO2 to the atmosphere it would result in increasing the global temperature by a catastrophic amount. I mean, it’s really only a question of how much CO2 it would take, right?

And whose opinion should we trust on that question, if not that of the overwhelming majority of climate scientists?

@Quartz

you might recall that there have been ice ages with higher CO2 concentrations. Therefore higher CO2 levels do not necessarily mean an increased greenhouse effect.

All that shows is that other factors can counterbalance the effect of CO2 levels on temperature. Which is largely irrelevant unless we have some reason to think we can count on other factors to counterbalance the effect of our CO2 emissions for the indefinite future. Couldn’t non-CO2 factors just as easily serve to further increase the temperature over the course of the next century?

If there’s even a 50% chance that the effects of unchecked human CO2 emissions will be as bad as most climate scientists predict or worse, then isn’t that already a pretty damn compelling reason to try to limit those emissions?

[Leaffan]

@tim314

It seems to me that it’s pretty obvious that if we add enough CO2 to the atmosphere it would result in increasing the global temperature by a catastrophic amount. I mean, it’s really only a question of how much CO2 it would take, right?

It seems to you, therefore it must be fact?

It’s not proven. See my earlier post in this thread. There are a lot of scientists and climatologists who do not believe in this theory.

Also, the average global temperature has not increased in 10 years, and in fact went down by 0.7 C this year (2007). Sun spots are the culprit: not CO2.

[intention]

tim314, welcome to the melee …

You say:

@tim314

It seems to me that it’s pretty obvious that if we add enough CO2 to the atmosphere it would result in increasing the global temperature by a catastrophic amount. I mean, it’s really only a question of how much CO2 it would take, right?

This is the problem with dealing with a very complex system. Things that are “pretty obvious” may not work that way at all.

For example, it’s pretty obvious that if you stick one end of a 160 pound hunk of solid stuff into water at 110°F, it will warm up. So let’s test that … I stick one end of a block of copper into the hot water, yes, the copper warms up. I stick one end of a block of iron into the water, it warms up … tell you what, I weigh about 160 pounds, how about if I stick my feet into hot water …

Nope, I didn’t warm up in the slightest.

Why? Because like the climate, and unlike a hunk of inert “stuff”, there are a variety of systems (known and unknown) in both humans and the climate which react and respond to changes in temperature.

So in fact, although some things might be “pretty obvious”, that doesn’t mean that they work that way in reality.

Welcome to the wonderful world of stunningly complex systems, where even the most obvious ideas need to be tested …

w.

[jshore]

@Leaffan

It’s not proven.

Nothing in science is ever “proven”. That is a red herring. If you want to prove something, you have to stick to a closed logical system such as mathematics, not science where knowledge is arrived at inductively.

See my earlier post in this thread. There are a lot of scientists and climatologists who do not believe in this theory.

And, there are “lots” of scientists who don’t believe in evolution. (I know having just gone to see the movie “Expelled”…which I don’t recommend seeing if you have a weak stomach.) Within the peer-reviewed literature, however, the story in both cases is much more lopsided.

Also, the average global temperature has not increased in 10 years, and in fact went down by 0.7 C this year (2007). Sun spots are the culprit: not CO2.

Actually, linear regression shows that the trend over the last 8, 9, or 10 years in both the Hadcrut3 and NASA GISS records is positive, how strongly so depends on which temperature record and which number of years. In all cases there are large error bars so (at least for the Hadcrut3 record, I’m not sure about the NASA one) a trend of zero cannot be excluded. But, that is simply a statement about the large degree of variability in the climate system that makes it difficult to see any underlying trend over too short a time period. Such variability, by the way, is also seen in individual runs of climate models…See for example, Figure 1 in this paper. Clearly, in what intention likes to call “GCM-world”, we’d have skeptics in around 2020 noting the lack of a distinctive upward trend over the last several years…and yet, we observers from outside of GCM world can clearly see what the overall trend is over a longer period of time.

At some level, I think we all intuitively understand this. After all, after nearly 2 weeks of high temperatures upper 60s, 70s…and even into the mid 80s, this week temperatures here in Rochester are back in the 40s and 50s. Yet, I have yet to hear anyone conclude that this crazy idea that scientists have of there being something called a “seasonal cycle” whereby we are headed toward a season called “summer” and should be getting warmer is all hogwash. (Well, okay, if truth be told, I have heard a few people cynically ask “How did you enjoy our Rochester summer?” but I don’t think I’ll count that.)

As for the 0.7 C drop, you are referring to a comparison between January 2007 and January 2008. (And, I also think you are quoting the high end of what the different temperature data sets show…but whatever.) As one looks over shorter and shorter intervals, there is more variability…and similar year-upon-year drops and rises in monthly average global temperature have been seen before. And, by the way, the temperatures have already significantly recovered in February and March.

As for your attribution to sunspots, it is amazing that you have been able to come up with such an attribution given the attention that has been given to even finding any evidence of the 11-year sunspot cycle in the global temperature record with rather mixed results…If it is there at all, it is hard to see through the noise. It is much more likely that this drop is due to the fairly strong La Nina conditions in the tropical Pacific.

[tim314]

@tim314

It seems to me that it’s pretty obvious that if we add enough CO2 to the atmosphere it would result in increasing the global temperature by a catastrophic amount. I mean, it’s really only a question of how much CO2 it would take, right?

@Leaffan

It seems to you, therefore it must be fact?

It’s not proven. See my earlier post in this thread. There are a lot of scientists and climatologists who do not believe in this theory.

Also, the average global temperature has not increased in 10 years, and in fact went down by 0.7 C this year (2007). Sun spots are the culprit: not CO2.

You’re telling me if we made the atmosphere 20% CO2 it wouldn’t result in substantial warming? Because that’s all I said – that at some point the amount of CO2 would produce a dangerous level of warming. The remaining question is: at what point?

If you’re telling me no amount of CO2 could produce warming, you’re basically denying the whole idea of the “green house effect”. The vast majority of climatologists (as well as other scientists) would disagree with you.

Talking about whether temperature has gone up or down in the past X years is missing the point. Obviously, other effects sometimes make a bigger difference in the global temperature than the green house effect. But you can’t reasonably conclude from that that no amount of green house gasses would dominate over those other effects.

There’s a big difference between arguing “The green house effect hasn’t resulted in a significant global temperature increase in the last decade” or arguing “We can pump as much green house gas as we want into the air without producing a substantial global temperature increase.” If you’re disagreeing with my statement quoted above, you’re essentially claiming the later.

If you can’t disagree with my statement above, then like I said, it’s just a question of “How much is too much?” (And for those of use who aren’t professional climate experts, it’s a question of “Whose opinion on how much is too much is it most reasonable to rely on?”)

[intention]

jshore, you note quite correctly that:

@jshore

Actually, linear regression shows that the trend over the last 8, 9, or 10 years in both the Hadcrut3 and NASA GISS records is positive, how strongly so depends on which temperature record and which number of years. In all cases there are large error bars so (at least for the Hadcrut3 record, I’m not sure about the NASA one) a trend of zero cannot be excluded.

That, of course, is using standard statistics (adjusted for autocorrelation).

I have previously brought up the matter of the IPCC’s curious use of terms to describe probabilities, which you seem to approve of. These are:

Virtually Certain >99% chance
Very Likely >90% chance
Likely >66% chance
More Likely Than Not >50% chance

So we could, on the other hand, use the IPCC’s strange definitions, in which case we’d say it is “likely” that the temperature trends have been negative over the past 7, 6, 5, 4, 3, and 2 years …

Now, as a huge fan of the IPCC, you’d have to agree with their assessment that it is likely that the world has been cooling since around the turn of the century, and ever since … care to comment on the implications of this likely cooling?

w.

PS - I bring this up again, not because I think there is any statistically significant recent cooling (I don’t), but to highlight the fact that the IPCC is a political rather than a scientific organization, and their terminology reflects that.

[brazil84]

@tim314

You’re telling me if we made the atmosphere 20% CO2 it wouldn’t result in substantial warming? Because that’s all I said – that at some point the amount of CO2 would produce a dangerous level of warming. The remaining question is: at what point?

I think it’s a bit of an academic question, but basically I agree with intention. It’s not obvious what would happen to the Earth’s climate if CO2 levels rose to 20%. For example, it’s possible that such a rise would have a profound impact on life, which in turn would have a profound impact on the climate.

In any event, above you ask whether we should trust the opinions of an “overwhelming majority of climate scientists”

Well, first things first: What exactly is the opinion of the overwhelming majority of climate scientists? According to this group of scientists, what level of CO2 will produce catastrophic warming?

[tim314]

@brazil84

I think it’s a bit of an academic question, but basically I agree with intention. It’s not obvious what would happen to the Earth’s climate if CO2 levels rose to 20%. For example, it’s possible that such a rise would have a profound impact on life, which in turn would have a profound impact on the climate.

Well, sure, maybe it could cause some other disastrous consequences that would somehow end up changing the climate in an unpredictable way. It’s not as if that’s a good thing.

But the immediate effect of adding a whole lot of CO2 to the air would be warming via the greenhouse effect. This is very well understood science. What drives me nuts is people trying to argue that CO2 doesn’t cause warming, based on looking at changes in temperature in the past. As I said, obviously there have been times when CO2 levels went up and temperature went down, but that just shows that other factors besides CO2 levels also effect global temperature, sometimes to a greater degree than CO2. (But again, there’s no reason to expect those other factors will always work to counter any warming due to CO2, as opposed to adding to it.)

But that has nothing to do with the fundamental reason for believing CO2 causes warming, which is a basic understanding of the physics of CO2. CO2 absorbs infrared radiation. The Earth radiates heat in the form of infrared radiation. It follows from this that, all other things being equal, adding CO2 to the atmosphere will result in a higher temperature at the surface of the Earth.

You don’t need a Ph.D. in climatology to understand that CO2 causes warming, just a basic understanding of physics. Then, as I said, the question becomes: How much warming? (Or: How much CO2 would it take to produce a disastrous amount of warming?)

[tim314]

Expanding on my post directly above this one…

I’d think that before there can be any serious discussion of global warming we’d at least need to agree on the following:

Adding CO2 to the atmosphere will cause:
(1) warming, due to the well understood mechanism of the greenhouse effect
(2) possibly other unpredictable effects

(I don’t know enough about climate science to know how fully other effects of CO2 have been explored, but I grant you point (2) for the sake of argument.)

There’s no reason to expect any other effects will make things better, so if a disastrous level of warming is predicted due to the green house effect alone, we should be deeply, deeply concerned.

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.

[brazil84]

@tim314

Well, sure, maybe it could cause some other disastrous consequences that would somehow end up changing the climate in an unpredictable way. It’s not as if that’s a good thing.

Yes, and you shouldn’t dismiss this as a trivial point.

Because fundamentally, the CAGW hypothesis rests on the idea that CO2 will cause a small temperature increase, which will interact with the rest of the climate in some way so as to multiply any warming from CO2.

These sorts of interactions are very difficult to predict. As was pointed out earlier in the thread, if you understand 95% of a complex, chaotic system, it doesn’t mean that your predictions will be 95% accurate. The last 5% can easily throw everything off.

But the immediate effect of adding a whole lot of CO2 to the air would be warming via the greenhouse effect. This is very well understood science.

Yes, but what’s not well understood is the longer term effects and interactions. And the CAGW hypothesis rests on predictions about the longer term effects and interactions.

That’s a big part of the reason why the hypothesis is so shaky.

[brazil84]

@tim314

There’s no reason to expect any other effects will make things better,

Actually, there’s very good reason to expect that other effects will counter any increased greenhouse warming from CO2. As far as anyone knows, the past few billion years have seen both higher and lower CO2 levels than today; as well as higher and lower global temperatures than today. And yet global temperatures and conditions on Earth have bounced around within a range that is not outrageously wide. This suggests that there are strong negative feedback mechanisms in the climate which keep global temperatures from wandering really high or really low.

[jshore]

@brazil84

Actually, there’s very good reason to expect that other effects will counter any increased greenhouse warming from CO2. As far as anyone knows, the past few billion years have seen both higher and lower CO2 levels than today; as well as higher and lower global temperatures than today. And yet global temperatures and conditions on Earth have bounced around within a range that is not outrageously wide. This suggests that there are strong negative feedback mechanisms in the climate which keep global temperatures from wandering really high or really low.

Hmmm…That’s not what these scientists who actually study paleoclimatic evidence seem to think:

Climate models and efforts to explain global temperature changes over the past century suggest that the average global temperature will rise by between 1.5º and 4.5ºC if the atmospheric CO2 concentration doubles. In their Perspective, Schrag and Alley look at records of past climate change, from the last ice age to millions of years ago, to determine whether this climate sensitivity is realistic. They conclude that the climate system is very sensitive to small perturbations and that the climate sensitivity may be even higher than suggested by models.

[brazil84]

@jshore

Hmmm…That’s not what these scientists who actually study paleoclimatic evidence seem to think:

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?

[tim314]

@brazil84

Actually, there’s very good reason to expect that other effects will counter any increased greenhouse warming from CO2. As far as anyone knows, the past few billion years have seen both higher and lower CO2 levels than today; as well as higher and lower global temperatures than today. And yet global temperatures and conditions on Earth have bounced around within a range that is not outrageously wide. This suggests that there are strong negative feedback mechanisms in the climate which keep global temperatures from wandering really high or really low.

How high is “really high” or “really low”? I’d think that some of the extremes of temperature we’ve seen over the past few billion years would be pretty darn bad for human civilization as it exists today. If these negative feedback mechanisms do exist but only become a dominant effect at the greatest temperature extremes of the last few billion years, it won’t necessarily do us much good.

@brazil84

These sorts of interactions are very difficult to predict. As was pointed out earlier in the thread, if you understand 95% of a complex, chaotic system, it doesn’t mean that your predictions will be 95% accurate. The last 5% can easily throw everything off.

My point, though is we don’t need 95% accuracy to be concerned by the predictions. I’d argue that even a 50% chance of a disastrous temperature increase would be reason enough for action. If a doctor told me I had a 50% chance of dying unless I took some expensive medicine, you can bet I’d buy the medicine, since a 50% chance of death is an unacceptable risk. Likewise, a 50% chance of a disastrous temperature increase is an unacceptable risk.

If we take the majority view of climate scientists as a median estimate, then even if there’s a huge amount of uncertainty in that number (which I don’t think these scientists actually admit to being the case), that still leaves a 50% chance that it will be as bad as they predict or worse.

[tim314]

Let me put it another way:

In order to justify reducing CO2 emissions, climate scientists don’t need to be able to predict the temperature some number of years from now to within some maximum error.

All they need to be able to predict is that it will be at some disastrous level or greater, with a confidence level that constitutes an unacceptable level of risk.

That is:
If D is the temperature we call “disastrous”, they don’t need to say the temperature will be:
T = D + or - s
for some small s

They just need to say the temperature will be:
T > D
with confidence level C, where C is greater than the maxmimum risk we’re willing to tolerate that the temperature will be greater than D.

That’s a much easier claim to make, particularly if C isn’t much more than 50%.

[tim314]

To reiterate: Of course many climate scientists do claim to be able to make much more precise predictions, but my point is you don’t need to believe in the precision of their predictions to be seriously concerned about climate change due to CO2 emissions. You just need to accept that number as a reasonable median value for how we can expect the temperature to change.

If some well understood processes (like the greenhouse effect) predict a temperature increase of X, then even if there remains the possibility of other unknown or unpredictable processes affecting temperature, it makes sense that X should be your median value in your estimate of future temperatures. (I say “median” to emphasize the 50% chance that things are worse – really our estimated probability distribution of possible temperatures would be symmetric around this point barring some reason to think the scientists are more likely to be overestimating than underestimating – so the median and the mean are the same.)

[brazil84]

@tim314

How high is “really high” or “really low”?

Here’s a video you might find interesting:

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

My point, though is we don’t need 95% accuracy to be concerned by the predictions. I’d argue that even a 50% chance of a disastrous temperature increase would be reason enough for action.

In a chaotic and complex system, you might not be able to predict things with any accuracy at all.

If we take the majority view of climate scientists as a median estimate, then even if there’s a huge amount of uncertainty in that number (which I don’t think these scientists actually admit to being the case), that still leaves a 50% chance that it will be as bad as they predict or worse.

Please show me a cite that > 50% of climate scientists are predicting catastrophe. If you link to an IPCC report, please quote the precise language that backs up your claim. TIA.

[intention]

tim314, a couple of points.

First, you say:

@tim314

I’d think that before there can be any serious discussion of global warming we’d at least need to agree on the following:

Adding CO2 to the atmosphere will cause:
(1) warming, due to the well understood mechanism of the greenhouse effect
(2) possibly other unpredictable effects

(I don’t know enough about climate science to know how fully other effects of CO2 have been explored, but I grant you point (2) for the sake of argument.)

Most scientists expect some warming from CO2. However, will it be a hundredth of a degree, or ten degrees? That’s where the dispute lies. So agreement on your points does not help much.

The problem is that, while the mechanism of the greenhouse effect (the way it works) is understood, it does not exist in isolation. It is a small part of a huge and complex system. There is no theoretical or practical reason to assume that it will work in that system in the way that it does in theory. Reconsider my example above, about putting one end of a block of copper into a bucket of warm water, and putting my feet into that same bucket.

Yes, the “well understood mechanism” of conductive heat transfer is at work in both cases. Yes, the theory is clear about how heat is transferred and the like … but when it is part of a complex system, all bets are off. In particular, you say:

@tim314

you don’t need to believe in the precision of their predictions to be seriously concerned about climate change due to CO2 emissions. You just need to accept that number as a reasonable median value for how we can expect the temperature to change.

OK, we look at how much the water theoretically warms a block of copper, and a block of steel, and a block of wood. We take the median value of a number of scientist’s estimates … but that still doesn’t tell us how much the human body will warm if we stick our feet in the bucket.

Best regards,

w.