Hi Ken,
Unfortunately I had to simplify the analogy somewhat - into just brakes
and throttle. But the oscillations I refer to are the coming and going
of the glacial periods over the past 2.5 million years or so. I
believe the temperature records, inasmuch as we have them, show that
the maximum temperatures at the end of each period of deglaciation are
remarkably similar to one another, the minima less so. The global
temperature today is only slightly below the maximum at the end of the
Eemian warming, when sea-level was 4-6 metres higher (maximum 2 metres
from Greenland, rest from Antarctic) [1].
Here's a quote from an article on the Pleistocene temperature [2]:
"Analysis of the d18O record
indicates two basis [sic] climate states, one glacial and one
interglacial.
Evidence for these bistable climate state is further provided by oxygen
isotope analysis of numerous ice cores. Figure 5.10 shows a d18O profile along the Camp Century
(Greenland) ice core (Dansgaard et al.,
1984) for the last 130,000 years. The record clearly reveals the last
major interglacial period at about 120 thousand years (Ka) and the
ensuing glaciation."
Cheers,
John
[1] http://en.wikipedia.org/wiki/Eemian
[2] http://www.global-climate-change.org.uk/5-3-1.php
---
Ken Caldeira wrote:
This idea of two stable states has been pushed recently by
Jim Lovelock, however I think there is very little evidence to support
such a view.
Just about every model result indicates monotonically and more-or-less
continuously increasing effect with increasing doses of CO2 (or changes
in sunlight).
[Of course, the models are a gross simplification of reality.]
There are a few sources of metastability (eg, large ice sheets) but I
do not think that these sources of metastability govern the overall
behavior of the system on sub-millennial time scales.
___________________________________________________
Ken Caldeira
Carnegie Institution Dept of Global Ecology
260 Panama Street, Stanford, CA 94305 USA
[email protected]
http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab
+1 650 704 7212; fax: +1 650 462 5968
On Mon, Dec 7, 2009 at 6:22 AM, John Nissen <[email protected]>
wrote:
Hi all,
I've a simple picture of the situation. Think of the Earth system as a
bus, with automatic speed control mechanism to keep the bus between two
speeds - a top speed and a bottom speed. When the bus gets to the top
speed the brakes automatically come on and the throttle starts
closing. Then when it has slowed to the bottom speed the brakes
automatically come off and the throttle starts opening again. This
mechanism has worked for over a million years, keeping the bus running
between higher and lower speeds, without the driver doing anything.
[Global temperature has oscillated between a top and bottom
temperature over the course of the Ice Ages. The Arctic sea ice is
probably involved in preventing the temperature going above the top
limit. CO2 may be involved in preventing the temperature going below
the bottom limit.]
Then, about 8000 years ago, when the bus was near its top speed, the
driver took over control. Although the brakes were starting to come
on, the throttle was kept open by the driver by just the right amount
to keep the bus going at the higher speed. This kept the passengers
extremely happy! They thought this situation would carry on for ever,
but this proved to be wishful thinking.
[By amazing chance, mankind's inadvertent emissions of CO2 and
methane have kept global temperature, and hence sea level, pretty
constant for about 8000 years, thus allowing the emergence of
civilisation.]
Then suddenly, a hundred years ago, the driver started opening the
throttle more than it had ever been before, whilst at the same time
taking off the break. Surprise, surprise, the bus started to
accelerate. Some passengers refused to see the danger - they were
enjoying the speed, and were happy for the driver to open the throttle
even more. Other passengers saw the danger. The passengers broke into
argument, and eventually agreed on a compromise to gradually stop
opening the throttle, although it was realised the bus could reach a
dangerous speed.
[Mankind has injected a colossal pulse of CO2 in the atmosphere,
which continues to grow, and will continue to grow under any Copenhagen
agreement. Global warming is an inevitable consequence of the excess
CO2 (although other gases contribute, both positively and negatively).]
Nobody wanted to point out that, at this speed, the bus would become
unstable and almost certainly crash off the road putting everybody's
life at risk. Thus it was actually in everybody's interest to close
the throttle and apply the brakes straight away. The compromise they
had reached just gave a false sense of security.
[Nobody seems willing to point out that our present path, akin to
business as usual, could lead to the collapse of our civilisation, e.g.
through famine. Any deal at Copenhagen is liable to engender a false
sense of security.]
Soon after the compromise had been reached, the bus, already travelling
dangerously fast, skidded on some ice, which the driver saw too late,
hit a tree and burst into flames, killing all on board.
[Tipping points have been ignored. The Arctic sea ice could
disappear quite rapidly, with potentially lethal consequences from
methane release and/or Greenland ice sheet disintegration. The Amazon
rainforest is also at risk of drought, leading to die off and burn.]
Sadly this fate was not inevitable. Unknown to the driver, there were
emergency brakes that could have slowed the bus, even while the
throttle was open. But the driver had been told that these emergency
brakes were too dangerous to use, so was not prepared to use them.
When he saw the ice, he tried to apply the emergency brakes but it was
too late.
[The only reasonable chance of saving the Arctic sea ice is through
the application of geoengineering to cool the region. The chance of
geoengineering successfully diminishes as positive feedbacks build up
in the Arctic. The more we delay geoengineering, the more we risk
passing a point of no return, so that a gruesome fate becomes
inevitable, possibly even for most people alive today.]
Cheers,
John
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