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temperature records can be contaminated |
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Written by editor
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Wednesday, 20 February 2008 |
Patrick J. Michaels
December 27, 2007
http://www.cato.org/pub_display.php?pub_id=8863
QUOTE: [S]ocioeconomic biases "likely add up to a net warming bias at
the global level that may explain as much as half the observed
land-based warming trend."
If a scientific paper appeared in a major journal saying that the planet
has warmed twice as much as previously thought, that would be front-page
news in every major paper around the planet. But what would happen if a
paper was published demonstrating that the planet may have warmed up
only half as much as previously thought?
Nothing. Earlier this month, Ross McKitrick from Canada's University of
Guelph and I published a manuscript in the Journal of Geophysical
Research-Atmospheres saying precisely that.
Patrick J. Michaels is senior fellow in environmental studies at the
Cato Institute and a member of the United Nations' Intergovernmental
Panel on Climate Change.
More by Patrick J. Michaels
Scientists have known for years that temperature records can be
contaminated by so-called "urban warming," which results from the fact
that long-term temperature histories tend to have originated at points
of commerce. The bricks, buildings, and pavement of cities retain the
heat of the day and impede the flow of ventilating winds.
For example, downtown Washington is warmer than nearby (and more rural)
Dulles Airport. As government and services expand down the Dulles Access
road, it, too, is beginning to warm compared to more rural sites to the
west.
Adjusting data for this effect, or using only rural stations, the United
Nations' Intergovernmental Panel on Climate Change states with
confidence that less than 10% of the observed warming in long-term
climate histories is due to urbanization.
That's a wonderful hypothesis, and Ross and I decided to test it.
 Convincing people is tough
We noted that other types of bias must still be affecting historical
climate records. What about the quality of a national network and the
competence of the observers? Other factors include movement or closing
of weather stations and modification of local land surfaces, such as
replacing a forest with a cornfield.
Many of these are socioeconomic, so we built a computer model that
included both regional climatic factors, such as latitude, as well as
socioeconomic indicators like GDP and applied it to the IPCC's
temperature history.
Weather equipment is very high-maintenance. The standard temperature
shelter is painted white. If the paint wears or discolors, the shelter
absorbs more of the sun's heat and the thermometer inside will read
artificially high. But keeping temperature stations well painted
probably isn't the highest priority in a poor country.
IPCC divides the world into latitude-longitude boxes, and for each of
these we supplied information on GDP, literacy, amount of missing data
(a measure of quality), population change, economic growth and change in
coal consumption (the more there is, the cooler the area).
Guess what. Almost all the socioeconomic variables were important. We
found the data were of highest quality in North America and that they
were very contaminated in Africa and South America. Overall, we found
that the socioeconomic biases "likely add up to a net warming bias at
the global level that may explain as much as half the observed
land-based warming trend."
We then modified IPCC's temperature data for these biases and compared
the statistical distribution of the warming to the original IPCC data
and to satellite measures of lower atmospheric temperature that have
been available since 1979. Since these are from a single source (the
U.S. government), and they don't have any urban contamination, they are
likely to be affected very little by economic factors.
Indeed. The adjusted IPCC data now looks a lot like the satellite data.
The biggest change was that the high (very warm) end of the distribution
in the IPCC data was knocked off by the unbiasing process.
Where was the press? A Google search reveals that with the exception of
a few blog citations, the only major story ran in Canada's Financial
Post.
There are several reasons why the press provides so little coverage to
science indicating that global warming isn't the end of the world. One
has to do with bias in the scientific literature itself. Theoretically,
assuming unbiased climate research, every new finding should have an
equal probability of indicating that things are going to be more or less
warm, or worse-than-we-thought vs. not-so-bad.
But, when someone finds that there's only half as much warming as we
thought, and the story is completely ignored, what does this say about
the nature of the coverage itself? Somehow, you'd think that would have
been newsworthy.
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Last Updated ( Wednesday, 20 February 2008 )
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