November 12, 2006
1 reviews the basic science. If you have as short attention span
as some we won't name, you can squash it into three of Stern's
The earth is warming
Chart page 5, sorry for the poor quality:
hockey stick is an irrelevance. What does it matter if it was as hot
in 1206 as now? We know that 1206 and 2006 both offered liveable
climates, unless you live in New Orleans. But they weren't doing
anything much in 1206 that could change their global environment for
the worse, and we are.
Chart page 4:
rising levels of greenhouse gases provide the only plausible
explanation for the
observed trend for at least the past 50 years
.... The causal link between greenhouse gases concentrations and
global temperatures is well established, founded on principles
established by scientists in the nineteenth century." (Stern
There's a smoking chimney: fossil
Chart p. 175:
fuels accounted for over 60% of the greenhouse gas emissions in 2000
(p.171). The growth rates in emissions from deforestation and other
land use changes were roughly parallel to those in fossil fuels back
to 1950, when the data for the former give out.
much is common ground. Even George Bush accepted the reality of
anthropogenic climate change in his Rose
Garden speech in June 2001.
I found most interesting in this part of the Stern report was its
discussion on the origin of the science (Wikipedia links added):
understanding of the greenhouse effect has its roots in the simple
calculations laid out in the nineteenth century by scientists such
Fourier realised in the 1820s that the atmosphere was more permeable
to incoming solar radiation than outgoing infrared radiation and
therefore trapped heat. Thirty years later, Tyndall identified the
types of molecules (known as greenhouse gases), chiefly carbon
dioxide and water vapour, which create the heat-trapping effect.
Arrhenius took this a step further showing that doubling the
concentration of carbon dioxide in the atmosphere would lead to
significant changes in surface temperatures.
underlying physics is rock-solid, unexciting stuff. (You can check
out some of it yourself. I've built a toy model that does this, too
childish for posting here, so it's tucked
away here on my personal website). It doesn't fit the Romantic,
Promethean story revived by Thomas Kuhn, of lonely geniuses
struggling to overthrow an inferior paradigm embedded in a consensus
conventional wisdom. There's no equivalent here to phlogiston, the
ether, heliocentrism, or special creation of species, strong
explanatory accounts with wide support. It's much more like the
Baconian story of electricity: first there wasn't any science, then
Ampère, Faraday, Ohm etc. made some observations, and after a
bit of to-ing and fro-ing knocked it into a perfectly sound theory.
New bits are being added all the time, but there's no fundamental
debate as with cosmology or sociobiology.
models use the laws of nature to simulate the radiative balance and
flows of energy and materials. These models are vastly different
from those generally used in economic analyses, which rely
predominantly on curve fitting. (Stern p.8)
scientists are used to models where the underlying theory is almost
as with microeconomics, and at best gives you the direction of a
causal link. To build a quantitative
model, you have to tweak the model parameters till they fit the
data. There's no deep reason why the elasticities in an economic
model should be what they are. The basic laws in climate models,
physical or chemical, are quantitative.
Potentially, climate models can be far superior to economic ones,
and Stern claims they already are. They are certainly much bigger.
I'm one of 60,000 volunteering my PC to a distributed climate
simulation; my run will be 1850 hours of CPU time when it's
finished, and that's just one
run of one
component of one
can't challenge the basic science, as it's secure textbook stuff.
But since the interactions are numerous, a climate model gets
forbiddingly complex and pushes against the frontiers of
computability. The uncertainties arise in the way the models are put
the next post I'll have a look at the controversial science:
predictions, sensitivities, and should we give the surviving
sceptics air time?
you found this too elementary, join the discussion at
realclimate.org instead. I
don't propose to compete with climate scientists.