----- Original Message -----
From: "James Annan" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, August 02, 2006 1:01 PM
Subject: [Global Change: 439] Re: Hansen: The Threat to the Planet
>
> [EMAIL PROTECTED] wrote:
>> I thought all SRES scenarios explicitly excluded any attempts at
>> reducing emissions of greenhouse gases.
>
> Yes and no. They exclude any deliberate attempts to cut GHG emissions
> which might be made for the specific purposes of mitigating climate
> change, but they include any deliberate attempts which we might make to
> cut the emissions of GHGs for any other reasons (such as due to other
> other environmentally disagreeable effects they might have), and they
> also include the effect of any cuts that might occur as a more-or-less
> incidental consequence of other policies or non-policies (energy
> efficiency, energy independence, technological advances, population
> changes, ...).
Surely that is not true? A scenario is just a scenario, a line on a graph
which shows the concentration of CO2 against future time. Whether
CO2 rises because the global economy is expanding or because the
permafrost is melting is irrelevant, if the shape of the subsequent graph is
the same. If the level of CO2 falls, then whether it is caused by
measures brought in by governments to protect the environment, or
because the oil has run out, will make no difference to the climatic
consequences. We don't know which scenario is correct, but we
can say that if we continue with business as usual, as Hansen is pointing
out, then the consequences will be catastrophic.
What Hansen is missing is that even if we do start cutting back on
CO2 emissions now, it will still be catastrophic. We have already
passed the tipping point. Hansen seems to think that since his
"alternative scenario yields an increase of less than two degrees
Fahrenheit during the same period [this century]..." then although
it "..., still produces a significant rise in the sea level, but its slower
rate, probably less than a few feet per century, would allow time to
develop strategies that would adapt to, and mitigate, the rise in the
sea level.
However, we already know that the Greenland ice is melting, and
that the rate of melt is accelerating. Unless we actually reduce the
amount of CO2 in the atmosphere, then that melting will continue to
accelerate. His alternative scenario does not propose that, only a
stabilization of CO2 by 2050.
Hansen also wrote: "Warming can be predicted accurately based
on knowledge of how Earth responded to similar levels of greenhouse
gases in the past. (By drilling into glaciers to analyze air bubbles
trapped under layers of snow, scientists can measure the levels of
each gas in the atmosphere hundreds of thousands of years ago.
By comparing the concentrations of different isotopes of oxygen
in these air bubbles, they can measure the average temperature
of past centuries.)" But the highest concentrations of CO2 recorded
in the ice cores are 300ppm when global temperatures were 2C
higher during the Eemian. Nowhere in the ice cores is a level of
400 ppm recorded, which will be the average level during the
next 50 years according to his alternative scenario.
Hansen now admits that Gore was correct when he asked for help
from Hansen 10 years ago. But although he has caught up with
Gore's views of ten years ago, Hansen is still ten years behind the
times. We do not have ten years in which to act. We must start now,
otherwise the accelerating melt of the Greenland ice will be
unstoppable!
Cheers, Alastair.
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