Re: [asa] UN Downgrades Man's Impact On The Climate

From: Rich Blinne <rich.blinne@gmail.com>
Date: Tue Dec 12 2006 - 16:55:46 EST

On 12/11/06, PvM <pvm.pandas@gmail.com> wrote:
more frequent heat waves and storms.
>
> The Telegraph report is obviously wrong. The IPCC report just
> summarizes the scientific literature. There has not been any paper
> published that would justify reducing the estimate. The reporter has
> confused climate sensitivity (how much warming you eventually get from
> doubling CO2), with predicted warming in 2100. In the third assessment
> report the top end of the range for sensitivity was 4.5, while the top
> end for warming by 2100 was 5.8. These numbers haven't changed in the
> new report, all that has happened is that the reporter has mistaken
> the 4.5 number for sensitivity as a new estimate for warming and
> reported it as a reduction from 5.8.

In fact, what has happened is the climate sensitivity numbers remained
the same but the error bars have come in since the last IPCC report.
We have the same numbers with higher confidence.

Even though we may believe we have a better handle on climate
sensitivity from five years ago we may be missing something that calls
into question whether 4.5 is truly the upper end of climate
sensitivity. In other words, unlike what Janice noted we may be under
rather than overestimating climate sensitivity.The Paleocene-Eocene
Thermal Maximum (PETM) is providing a quandary. Given our current
climate sensitivity numbers we have to explain a lot (5400 to 112,000
PgC) of Carbon released during the PETM. The extraordinary magnitude
of these estimates is evident when compared against the 5000 PgC
estimated for conventional fossil fuel resources available today. If
you assumed a carbon input of 1800 to 3500 PgC in order to explain
the >5 degrees C temperature rise would give a climate sensitivity of
6.8 to 7.8C per CO2 doubling. If this is indeed correct then the
64,000 dollar question is this applicable to today, implying we are
lowballing the climate sensitivity.

See http://www.sciencemag.org/cgi/content/full/314/5805/1556 (Science
8 December 2006: Vol. 314. no. 5805, pp. 1556 - 1557)
for more details. Here's their conclusion:

These details may appear esoteric, but to determine the mass and
source of carbon responsible for the >5C warming during the PETM, we
must match the magnitude of the carbon isotope excursion with the mean
global temperature sensitivity to CO2 and associated climate feedbacks
(see the figures). One conclusion from this approach is that CO2
derived from methane hydrates could only have caused the PETM if the
climate sensitivity to CO2 was much higher than currently assumed. Yet
carbon sources other than methane, such as the oxidation of primary
terrestrial and/or marine organic carbon, together with commonly
accepted estimates of climate sensitivity, would require extremely
large carbon inputs to explain the warming. Thus, the PETM either
resulted from an enormous input of CO2 that currently defies a
mechanistic explanation [RDB Note: or we could blame George W. Bush
:-) ], or **climate sensitivity to CO2 was extremely high**. [emphasis
mine]

The next challenges are to constrain the magnitude and rate of carbon
input (and that of other greenhouse gases) and to develop realistic
models for the cause of this anomalous, but clearly CO2-induced global
warming event. Solving this mystery will allow us to determine whether
the PETM is a true analog for future climate change.

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Received on Fri Dec 15 02:01:41 2006

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