Re: [asa] Global Cooling

From: Rich Blinne <>
Date: Tue May 12 2009 - 21:05:53 EDT

On Tue, May 12, 2009 at 8:43 AM, Jon Tandy <> wrote:

> This may have been discussed sometime in the past, but I would like
> someone to give a concise description of what happened with the "global
> cooling" scare back in the 1970's. Not something from the anti-global
> warming advocates, who trumpet this rhetorically to show that "scientists
> don't really understand the environment, and the global warming scare will
> probably a memory in another decade," but a summary from someone (on list or
> in an Internet link) who understands the current global warming consensus.
> Why was there a global cooling prediction (or is this even an overblown
> view of history), and what led to those predictions that eventually proved
> to be incorrect?
> If there were unknowns that led to that failed prediction, how do we know
> that the current warming predictions are on target and unlikely to be
> overturned? In other words, what assurance do we have that this won't be a
> non-issue 10 years from now, as the AGW lobby claims?
> Jon Tandy

It's overblown history given the disdain of the sceptics about peer-reviewed
literature. The cooling hysteria was pumped mostly by the news weeklies. The
peer-reviewed literature was much more sober. The consensus at the time was
it was unknown whether the temperature would heat or cool. There were two
things going on in the 70s that need to be kept separate, cooling due to
natural causes and cooling due to sulfate aerosols. Also what also needs to
be kept separate is the peer-reviewed technical literature and Time and
Newsweek. I will focus on the former.

1. An attempt was made in the 70s to predict when the next ice age that was
*independent of anthropogenic factors*. There was speculation whether this
was imminent where imminent meant on a centennial or millennial time scale.
Interpretations of future changes in the Earth's orbit have changed
somewhat. It now seems likely (Loutre and Berger, Climatic Change, 46: (1-2)
61-90 2000) that the current interglacial, based purely on natural forcing,
would last for an exceptionally long time: perhaps 50,000 years.

2. At the time the temperature record was showing cooling. Climatologists at
the time knew that CO2 would cause warming and sulfate aerosols would cause
cooling. What they didn't know was which was going to be dominate. In 1975
the NAS didn't declare either a warming or cooling world but rather that
they needed more data. We now know that this was just a slight interruption
of the warming trend. It turns out that the northern hemisphere cooling was
larger than the southern because the sulphate aerosols were predominately in
the NS. (Sulfates differ from CO2 and other greenhouse gases in that they
are not well mixed.) Only Northern Hemisphere records were available in the
70s. One paper that looked at the competing forcings was Rasool and
Schneider, Science, July 1971, p 138, "Atmospheric Carbon Dioxide and
Aerosols: Effects of Large Increases on Global
This paper had a number of flaws. First of all, even now you can only look
at small changes of CO2 or SO2 and expect good results. R&S was looking at
8x differences. They also underestimated the CO2 climate sensitivity by a
factor of 3. And they predicted far more aerosols than there ending up
being. This latter point is really unpredictable because the reason why they
underestimated aerosols was because the cap and trade of SO2 in the early
90s was spectacularly successful. Who talks about acid rain these days? Cap
and trade was responsible for that. IPCC projections of future temperature
inceases went up from the 1995 SAR to the 2001 TAR because estimates of
future sulphate aerosol levels were lowered
The bottom line is it's much easier to predict physical systems than it is
human behavior. That being said, predicting CO2 is easy because it's been
linearly increasing since the 50s when it was started being measured.

Helpful web sites on the topic:

Rich Blinne
Member ASA

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Received on Tue May 12 21:06:24 2009

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