Geoscience Reference
In-Depth Information
It's the Anomalies, Stupid
Science advances, then, not simply through the confirmation of previous findings, but by scientists
trying to understand the data and observations that don't fit, that don't seem to make sense—the
anomalies. That too is scientific skepticism in action.
It was an interest in understanding such anomalies that drove my own research into past
climates. The Northern Hemisphere average temperature curve—the hockey stick—was in some
sense the least interesting aspect to me of our temperature reconstruction work. What was most
fascinating—and potentially instructive—wasn't the global trend, it was the features that bucked the
trend. What was so special about Europe that caused it to cool more than other regions during the
height of the Little Ice Age? Why did some proxy records appear to be pointing toward cold La Niña-
like conditions in the tropical Pacific during the height of what was supposed to be the medieval
warm period (or medieval climate anomaly), for example? These were the sorts of questions my
colleagues and I were keen to pursue. The hockey stick itself was a by-product, indeed almost an
afterthought.
I had always enjoyed an intriguing puzzle, especially one that called for novel and clever
approaches. Here was one. How could we figure out what dynamic aspects of the climate system
were leading to these perplexing regional features of the Little Ice Age and medieval climate
anomaly? In pursuing such questions, I collaborated with scientists who had been using theoretical
climate models to investigate the role of purely internal variability related, for example, to the
volcanoes.
Colleagues at the NASA Goddard Institute for Space Studies (GISS, located on Manhattan's
Upper West Side, literally sitting above Tom's Diner of
Seinfeld
fame) had been using their climate
my U. Mass. collaborators and I had been looking at the pattern of surface temperature changes in our
reconstructions associated with variations in solar output over time.
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We found that the decrease in
solar output during the Maunder minimum of the seventeenth century, while leading to global cooling
of only a few tenths of a degree Celsius, gave rise to much greater regional cooling (nearly a degree
in some places) over much of Eurasia and North America. Some regions, like western Greenland and
the Middle East, though, actually showed a temperature increase! Working with our GISS
collaborators, we were able to demonstrate that this pattern was consistent with the way a lowering
of solar output weakens the Northern Hemisphere jet stream, altering its north-south undulations, so
that some regions cool more than the global mean, while other regions cool less, or even warm.
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Other anomalies appeared to be related to the impact of volcanic eruptions on climate. In the
mid-1980s, a scientist named Paul Handler from the University of Illinois had suggested a
relationship between explosive tropical volcanic eruptions and the timing of major El Niño events,
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but his findings were based on only a short interval of time: the instrumental record available back
through the late nineteenth century. Other properly skeptical scientists argued that the statistical
relationship was not very robust—remove one major volcanic eruption, for example, and the
relationship is no longer statistically significant—and there was no convincing physical explanation
given for why this relationship between volcanic eruptions and El Niño events should exist in the first
place.
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