That is indeed the ultimate question. The answer lies within totally unknown and even unquestioned change. We know, for example, the Pliocene was … much warmer than today (how much warmer? I don’t know.) but the tropics were virtually the same as now. Was it a problematic clime? No indications thereof.

Then, even to get there we have to ask if indeed convection is the big buffer in all this anyway, which would make the tropics the same as now. Hmmm… sound familiar? Why does there appear to be a max ocean temp, and what does that mean for albedo and clouds?

I really don’t know, but the answer in terms of the biosphere itself is undoubtedly higher than the answer in terms of Homo sapiens. So we have a few choices. Some are the Luddite climate, the existing climate, the max in terms of technological food distribution, or the max in terms of biospheric robustness.

Whoever knows the answer to that is … intellectually incoherent.

OK. So which is worse…cooling 3 deg C over the next 100 years, or dropping 1 deg C, then gaining 3 degree C from that point, within the next 100 years? What about dropping 2 deg C, then gaining back 4 deg C? Do you think that’s worse than simply dropping 3 deg C? Or even dropping 2 deg C, and staying there?

“On average the temperatures rose at about 1/10th of the rapidity they are now rising at (~10oC over ~5Kyrs)”

Well, who in the world thinks the earth is going to warm 10 deg C over the next couple hundred or thousand years? Who even thinks the world is going to warm 5 deg C?

Do you honestly think a rise of 2 deg C in the next 100 years (which works out to a RATE of 20 deg C over 1000 years) is any big deal?

3oC in either direction in 100 years is a very rapid and significant change. Your other hypotheticals are rather strange. They also approach the timeframes one would more associate with weather.

For an example of a catastrophically large and fast change google for PETM, or search wikipedia for the paleocene-eocene thermal maximum.

If you look at the antarctic ice core records of glacial interglacial cycles you see what are more “normal” changes, extreme as they are. On average the temperatures rose at about 1/10th of the rapidity they are now rising at (~10oC over ~5Kyrs) and fell another order of magnitude slower.

So if the world gradually got 3 degrees Celsius colder over the next 100 years, that would be less of a problem than if the world decreased 1 degree Celsius in next 20 years, and then jumped up 3 degrees Celsius within one decade in 2030 (for a next change from present of plus 2 degrees Celsius)?

Steve Hemphill responded, “Well, definitely on the 2 deg C colder part, but maybe not on the 4 deg C warmer.”

Well, what number on the upper end *would* you give for what we could “pretty safely say…would be worse than now?”

Well, definitely on the 2 deg C colder part, but maybe not on the 4 deg C warmer.

Lately I have begun to think of people who want to return to the climate of hundreds of years ago as Climate Luddites…

Chip Knappenberger responded, “What exactly is ‘better weather’? And who is the judge? And if we could set the global thermostat anywhere we wanted (by changing light bulbs or other means), at what temperature would it be set and who would get to decide?”

This is a very significant question, or set of questions.

1) Is there an “optimum” global *average* temperature?

We can pretty safely say that, for example, 2 degrees Celsius colder than today (i.e., colder than during the Little Ice Age), and maybe 4 degrees Celsius warmer, would be “worse” than now.

But within that range, especially the closer one gets to the middle, the more difficult it is to make a judgement.

2) Is there an optimum global temperature *distribution*?

For example, it seems reasonable that the hotter areas right at the equator get (except those in the high mountains, like Ecuador) the worse off they are.

But if the Yukon or Siberia warmed by 5-10 degrees Celsius, would that be “bad?”

If the climate of Chicago was like Nashville, or Nashville like Tallahassee…would one or both of those changes be good, or bad?

To my knowledge, such questions aren’t even considered in any of the IPCC’s Assessments…at least so far. In my mind, that’s just one more piece of evidence that the Assessments are not truly comprehensive or balanced.

You suggest that:
“Carbon dioxide emissions cannot simply be “frozen.” This seems like exactly the sort of “high-minded debate about theoretical future reductions” that he just warned us about.”

I think there are many who believe that if the broad scientific consensus on global warming is credible, immediate efforts to level and reduce CO2 emissions are inevitable components of any plan to deal with the potential consequences, and that these efforts deserve to be treated as security issues (both national and global – which they certainly may be) . I would suspect that with programs supporting conservation and alternative energy research, development and distribution at a scale of, say, the interstate highway building program of the ‘50s and the Space program, emissions levels could be frozen within a few years. On alternative energy we’re not that far off except for the scale economy differentials that hamper any new entrants to a market. How much of a difference this would make in alleviating the climate situation must be evaluated keeping in mind that efforts such as Kyoto Protocol are intended as first steps to provide a foundation for further and more effective actions at emissions reductions. Kyoto focuses on the developed states partially because that is essentially where the current problems have emanated from, but also because it is expected that that developing states (from where much of the future increase in global emissions will emanate) will be more likely to follow suit with emissions commitments of their own in future negotiations if they see that developed states have taken the issue seriously and adopted proactive measures.

“Gore’s technological optimism on just about every other area of climate change policy does not square with his technological pessimism about nuclear power.”

I don’t think it’s a matter of tech optimism on nuclear power – he clearly states that he isn’t focusing on key tech issues such as “waste disposal or the danger of reactor operator error, or the vulnerability to terrorist attack.” He is focusing on economic and political factors that may be interrelated and that are not ultimately susceptible to technological control when he refers to, on the one hand the scale economics and, on the other had the increased likelihood of proliferation. Presumably, even if the size factor were to be solved and smaller, more plentiful and economic reactors were to become widespread, this would very likely lead to increased proliferation opportunities and problems.

Just my opinion,
Best,
MB