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Author: AstroPhool Three stars, 500 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 53639  
Subject: Re: Imagine if we enter a New Ice Age Date: 9/24/2013 8:41 PM
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LordFoolman:
And what you throw at me in the rest of your post is 1) you don't know what effects the ice age may have yet you you seem very confident of the rise of CO2 to 800 ppm and it driving temps to 2 C increase?

That's the crux of the argument. I would venture to guess that the rise of 800 ppm of CO2 (100% increase from today) - honestly I really don't see that happening at all. That's worse case.

A and secondarily, the issue of feedback effects. You seem to see a 1 Celsius rise from a doubling of of CO2 may lead to 2 C. I say that's even exaggerating reality.

You warmists have overshot your load. The public support has very much backed away. Even the most recent IPCC is backtracking.... And I see it continuing.

Best case the small warming from CO2 increases will be completely offset by the solar diminution, which is already being seen in the temp records. We simply ride a flat temp profile for a few decades. Worst case, we cool for 100-200 years and plant life growth slows. But we compensate. Either way we humans are smart enough to adequately compensate. Don't worry. And don't tear others down out of fear.


There's a lot of material covered here, but most of it is incorrect.

First, the feedback. The direct effect of climate on doubling CO2 is, as you say, about 1 C. But (fast) positive feedbacks, such as the increase in water vapor in the warmer atmosphere, increase this to give a climate sensitivity of between 2 and 3 C. This is reasonably well established. For example, this quantity is just the slope of the dT (temperature change) vs atmospheric CO2 regression line:

http://www.ap.smu.ca/~pbennett/climate/recentx_dt_co2.gif

and from this fit we get a climate sensitivity of 2.6 C. If dt is regressed on log CO2 instead (which is the more correct procedure), then a slightly lower sensitivity of 2.2 C is obtained.

But a significant proportion (about 50%) of the CO2 put into the atmosphere stays there for a 1000 years, with ~30% surviving for 10 kyrs. So the real question is: what will doubling CO2 have on the climate over that period?

The paleoclimate record shows a much steeper dT-CO2 relation, and that is presumably because these data give the climate response over thousands of years, and not over the years-to-decades that we measure with the modern record. There are a lot of positive feedbacks that take a long time to assert themselves. Most of these involved the melting of ice sheets in a warmer world, and that reduces the albedo and increases the warming further. This effect appears to be large, and the the slope of the paleoclimate (ice-core record) of the dT-CO2 relation (the left dataset, plotted with blue points) in the figure linked here:

http://www.ap.smu.ca/~pbennett/climate/parrenin_t_co2x.gif

implies a very large long-term effective climate sensitivity of 9.5 C for doubled CO2 when ice albedo feedbacks are included.

Introducing loaded terms like "alarmist" or "warmist" into the picture is not helpful. I've tried to present the science as I see it, and to leave the politics aside.

I am less sanguine than you about the prospect of reducing fossil-fuel emissions long-term. Unfortunately, this requires a concerted communal effort for long-term global benefit. However, the costs of reducing carbon emission are immediate and upfront, while the benefits will only accrue in the distant (> 100 yrs) future, and at that, remain somewhat uncertain. In the short-term, immediate financial benefits flow to those who do not bother to cut emissions. For example, why should the U.S. put money into reducing carbon emissions when China is still building more coal-fired generating plants? Humanity has never been good at responding to this kind of slow, long-term crisis of the commons.

Personally, I think fossil-fuel emissions will continue at present rates of increase (of 3 ppm/yr) for another century before being brought under control, and so we will see peak CO2 levels of about 700 ppm around 2100. My estimate is that this will lead to levels of CO2 of about 500 ppm and a warming of 6.5 C after 1000 years (i.e., CO2 levels will decline gradually from 700 ppm to 500 ppm over the millenium, but temperatures will continue to slowly warm over this same period). This, by any measure, is a disastrous level of warming that will melt all polar ice on the Earth, raise sea level by about 220 ft, and make the low-altitude tropics almost uninhabitable.

Thinking the Sun will save us is a fool's game. The Sun will only remain inactive for a couple of decades at most, and will recover. Any respite from the Sun will be small (about 0.15-0.20 C of cooling at best), and short-lived.

Phil
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