[Vision2020] The Conversion of a Climate-Change Skeptic

[Art Deco]

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July 28, 2012
The Conversion of a Climate-Change Skeptic By RICHARD A. MULLER

Berkeley, Calif.

CALL me a converted skeptic. Three years ago I identified problems in
previous climate studies that, in my mind, threw doubt on the very
existence of global warming. Last year, following an intensive research
effort involving a dozen scientists, I concluded that global warming was
real and that the prior estimates of the rate of warming were correct. I’m
now going a step further: Humans are almost entirely the cause.

My total turnaround, in such a short time, is the result of careful and
objective analysis by the Berkeley Earth Surface
Temperature<http://berkeleyearth.org/>project, which I founded with my
daughter Elizabeth. Our results show that
the average temperature of the earth’s land has risen by two and a half
degrees Fahrenheit over the past 250 years, including an increase of one
and a half degrees over the most recent 50 years. Moreover, it appears
likely that essentially all of this increase results from the human
emission of greenhouse gases.

These findings are stronger than those of the Intergovernmental Panel on
Climate Change, the United Nations group that defines the scientific and
diplomatic consensus on global warming. In its 2007 report, the I.P.C.C.
concluded only that most of the warming of the prior 50 years could be
attributed to humans. It was possible, according to the I.P.C.C. consensus
statement, that the warming before 1956 could be because of changes in
solar activity, and that even a substantial part of the more recent warming
could be natural.

Our Berkeley Earth approach used sophisticated statistical methods
developed largely by our lead scientist, Robert Rohde, which allowed us to
determine earth land temperature much further back in time. We carefully
studied issues raised by skeptics: biases from urban heating (we duplicated
our results using rural data alone), from data selection (prior groups
selected fewer than 20 percent of the available temperature stations; we
used virtually 100 percent), from poor station quality (we separately
analyzed good stations and poor ones) and from human intervention and data
adjustment (our work is completely automated and hands-off). In our papers
we demonstrate that none of these potentially troublesome effects unduly
biased our conclusions.

The historic temperature pattern we observed has abrupt dips that match the
emissions of known explosive volcanic eruptions; the particulates from such
events reflect sunlight, make for beautiful sunsets and cool the earth’s
surface for a few years. There are small, rapid variations attributable to
El Niño and other ocean currents such as the Gulf Stream; because of such
oscillations, the “flattening” of the recent temperature rise that some
people claim is not, in our view, statistically significant. What has
caused the gradual but systematic rise of two and a half degrees? We tried
fitting the shape to simple math functions (exponentials, polynomials), to
solar activity and even to rising functions like world population. By far
the best match was to the record of atmospheric carbon dioxide, measured
from atmospheric samples and air trapped in polar ice.

Just as important, our record is long enough that we could search for the
fingerprint of solar variability, based on the historical record of
sunspots. That fingerprint is absent. Although the I.P.C.C. allowed for the
possibility that variations in sunlight could have ended the “Little Ice
Age,” a period of cooling from the 14th century to about 1850, our data
argues strongly that the temperature rise of the past 250 years cannot be
attributed to solar changes. This conclusion is, in retrospect, not too
surprising; we’ve learned from satellite measurements that solar activity
changes the brightness of the sun very little.

How definite is the attribution to humans? The carbon dioxide curve gives a
better match than anything else we’ve tried. Its magnitude is consistent
with the calculated greenhouse effect — extra warming from trapped heat
radiation. These facts don’t prove causality and they shouldn’t end
skepticism, but they raise the bar: to be considered seriously, an
alternative explanation must match the data at least as well as carbon
dioxide does. Adding methane, a second greenhouse gas, to our analysis
doesn’t change the results. Moreover, our analysis does not depend on
large, complex global climate models, the huge computer programs that are
notorious for their hidden assumptions and adjustable parameters. Our
result is based simply on the close agreement between the shape of the
observed temperature rise and the known greenhouse gas increase.

It’s a scientist’s duty to be properly skeptical. I still find that much,
if not most, of what is attributed to climate change is speculative,
exaggerated or just plain wrong. I’ve analyzed some of the most alarmist
claims, and my skepticism about them hasn’t changed.

Hurricane Katrina cannot be attributed to global warming. The number of
hurricanes hitting the United States has been going down, not up; likewise
for intense tornadoes. Polar bears aren’t dying from receding ice, and the
Himalayan glaciers aren’t going to melt by 2035. And it’s possible that we
are currently no warmer than we were a thousand years ago, during the
“Medieval Warm Period” or “Medieval Optimum,” an interval of warm
conditions known from historical records and indirect evidence like tree
rings. And the recent warm spell in the United States happens to be more
than offset by cooling elsewhere in the world, so its link to “global”
warming is weaker than tenuous.

The careful analysis by our team is laid out in five scientific papers now
online at BerkeleyEarth.org. That site also shows our chart of temperature
from 1753 to the present, with its clear fingerprint of volcanoes and
carbon dioxide, but containing no component that matches solar activity.
Four of our papers have undergone extensive scrutiny by the scientific
community, and the newest, a paper with the analysis of the human
component, is now posted, along with the data and computer programs used.
Such transparency is the heart of the scientific method; if you find our
conclusions implausible, tell us of any errors of data or analysis.

What about the future? As carbon dioxide emissions increase, the
temperature should continue to rise. I expect the rate of warming to
proceed at a steady pace, about one and a half degrees over land in the
next 50 years, less if the oceans are included. But if China continues its
rapid economic growth (it has averaged 10 percent per year over the last 20
years) and its vast use of coal (it typically adds one new gigawatt per
month), then that same warming could take place in less than 20 years.

Science is that narrow realm of knowledge that, in principle, is
universally accepted. I embarked on this analysis to answer questions that,
to my mind, had not been answered. I hope that the Berkeley Earth analysis
will help settle the scientific debate regarding global warming and its
human causes. Then comes the difficult part: agreeing across the political
and diplomatic spectrum about what can and should be done.

Richard A. Muller <http://muller.lbl.gov/>, a professor of physics at the
University of California, Berkeley, and a former MacArthur Foundation
fellow, is the author, most recently, of “Energy for Future Presidents: The
Science Behind the Headlines.”


-- 
Art Deco (Wayne A. Fox)
art.deco.studios at gmail.com
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