I Was On the Global Warming Gravy Train
By David Evans
Posted on 5/28/2007
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[A version of tihs article was previously blogged on Mises.org here,
and inspired a spirited debate. The author reworked the piece for the
Mises.org front page. The blog item remains the same.]
I devoted six years to carbon accounting, building models for the
Australian government to estimate carbon emissions from land use
change and forestry. When I started that job in 1999 the evidence
that carbon emissions caused global warming seemed pretty conclusive,
but since then new evidence has weakened that case. I am now
skeptical.
In the late 1990s, this was the evidence suggesting that carbon
emissions caused global warming:
Carbon dioxide is a greenhouse gas, proved in a laboratory a century
ago.
Global warming has been occurring for a century and concentrations of
atmospheric carbon have been rising for a century. Correlation is not
causation, but in a rough sense it looked like a fit.
Ice core data, starting with the first cores from Vostok in 1985,
allowed us to measure temperature and atmospheric carbon going back
hundreds of thousands of years, through several dramatic global
warming and cooling events. To the temporal resolution then available
(data points more than a thousand years apart), atmospheric carbon
and temperature moved in lockstep: they rose and fell together. Talk
about a smoking gun!
There were no other credible causes of global warming.
This evidence was not conclusive, but why wait until we are
absolutely certain when we apparently need to act now? So the idea
that carbon emissions were causing global warming passed from the
scientific community into the political realm. Research increased,
bureaucracies were formed, international committees met, and
eventually the Kyoto protocol was signed in 1997 to curb carbon
emissions.
"Correlation is not causation, but in a rough sense it looked like a
fit."
The political realm in turn fed money back into the scientific
community. By the late 1990s, lots of jobs depended on the idea that
carbon emissions caused global warming. Many of them were
bureaucratic, but there were a lot of science jobs created too.
I was on that gravy train, making a high wage in a science job that
would not have existed if we didn't believe carbon emissions caused
global warming. And so were lots of people around me; there were
international conferences full of such people. We had political
support, the ear of government, big budgets. We felt fairly important
and useful (I did anyway). It was great. We were working to save the
planet!
But starting in about 2000, the last three of the four pieces of
evidence above fell away. Using the same point numbers as above:
Better data shows that from 1940 to 1975 the earth cooled while
atmospheric carbon increased. That 35 year non-correlation might
eventually be explained by global dimming, only discovered in about
2003.
The temporal resolution of the ice core data improved. By 2004 we
knew that in past warming events, the temperature increases generally
started about 800 years before the rises in atmospheric carbon.
Causality does not run in the direction I had assumed in 1999 it
runs the opposite way!
It took several hundred years of warming for the oceans to give off
more of their carbon. This proves that there is a cause of global
warming other than atmospheric carbon. And while it is possible that
rising atmospheric carbon in these past warmings then went on to
cause more warming ("amplification" of the initial warming), the ice
core data neither proves nor disproves this hypothesis.
There is now a credible alternative suspect. In October 2006 Henrik
Svensmark showed experimentally that cosmic rays cause cloud
formation. Clouds have a net cooling effect, but for the last three
decades there have been fewer clouds than normal because the sun's
magnetic field, which shields us from cosmic rays, has been stronger
than usual. So the earth heated up. It's too early to judge what
fraction of global warming is caused by cosmic rays.
There is now no observational evidence that global warming is caused
by carbon emissions. You would think that in over 20 years of intense
investigation we would have found something. For example, greenhouse
warming due to carbon emissions should warm the upper atmosphere
faster than the lower atmosphere but until 2006 the data showed the
opposite, and thus that the greenhouse effect was not occurring! In
2006 better data allowed that the effect might be occurring, except
in the tropics.
The only current "evidence" for blaming carbon emissions are
scientific models (and the fact that there are few contradictory
observations). Historically, science has not progressed by
calculations and models, but by repeatable observations. Some
theories held by science authorities have turned out to be
spectacularly wrong: heavier-than-air flight is impossible, the sun
orbits the earth, etc. For excellent reasons, we have much more
confidence in observations by several independent parties than in
models produced by a small set of related parties!
Let's return to the interaction between science and politics. By 2000
the political system had responded to the strong scientific case that
carbon emissions caused global warming by creating thousands of
bureaucratic and science jobs aimed at more research and at curbing
carbon emissions.
"Science has not progressed by calculations and models, but by
repeatable observations."
But after 2000 the case against carbon emissions gradually got
weaker. Future evidence might strengthen or further weaken it. At
what stage of the weakening should the science community alert the
political system that carbon emissions might not be the main cause of
global warming?
None of the new evidence actually says that carbon emissions are
definitely not the cause of global warming, there are lots of good
science jobs potentially at stake, and if the scientific message
wavers then it might be difficult to later recapture the attention of
the political system. What has happened is that most research efforts
since 1990 have assumed that carbon emissions were the cause, and the
alternatives get much less research or political attention.
Unfortunately politics and science have become even more entangled.
Climate change has become a partisan political issue, so positions
become more entrenched. Politicians and the public prefer simple and
less-nuanced messages. At the moment the political climate strongly
blames carbon emissions, to the point of silencing critics.
The integrity of the scientific community will win out in the end,
following the evidence wherever it leads. But in the meantime, the
effect of the political climate is that most people are
overestimating the evidence that carbon emissions are the main cause
of global warming.
I recently bet $6,000 that the rate of global warming would slow in
the next two decades. Carbon emissions might be the dominant cause of
global warming, but I reckon that probability to be 20% rather than
the 90% the IPCC estimates.
I worry that politics could seriously distort the science. Suppose
that carbon taxes are widely enacted, but that the rate of global
warming increase starts to decline by 2015. The political system
might pressure scientists to provide justifications for the taxes.
$15
Imagine the following scenario. Carbon emissions cause some warming,
maybe 0.05C/decade. But the current warming rate of 0.20C/decade is
mainly due to some natural cause, which in 15 years has run its
course and reverses. So by 2025 global temperatures start dropping.
In the meantime, on the basis of models from a small group of climate
scientists but with no observational evidence (because the small
warming due to carbon emissions is masked by the larger natural
warming), the world has dutifully paid an enormous cost to curb
carbon emissions.
Politicians, expressing the anger and apparent futility of all the
unnecessary poverty and effort, lead the lynching of the high priests
with their opaque models. Ironically, because carbon emissions are
raising the temperature baseline around which natural variability
occurs, carbon emissions might need curbing after all. Maybe. The
current situation is characterized by a lack of observational
evidence, so no one knows yet.
Some people take strong rhetorical positions on global warming. But
the cause of global warming is not just another political issue,
subject to endless debate and distortions. The cause of global
warming is an issue that falls into the realm of science, because it
is falsifiable. No amount of human posturing will affect what the
cause is. It just physically is there, and after sufficient research
and time we will know what it is.
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David Evans, a mathematician, and a computer and electrical engineer,
is head of Science Speak. Send him mail. Comment on the blog.
