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.
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.
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.
