Harvard researchers are adding statistical nuance to our understanding of how modern and historical temperatures compare.
Through developing a statistical model of Arctic temperature and how it relates to instrumental and proxy records derived from trees, ice cores, and lake sediments, Martin Tingley, a research associate in Harvard's Department of Earth and Planetary Sciences and Peter Huybers, Professor of Earth and Planetary Sciences, have shown that the warmest summers in the last two decades are unprecedented in the previous six centuries. Their work is described in an April 11 paper published in Nature.
"We call upon multiple proxies---including those derived from trees, ice cores, and lake sediments---to reconstruct temperature back through time using a Bayesian statistical approach," Tingley said. "What we are trying to do is put statistical inference of past changes in temperature on a more solid and complete footing."
"Saying this year is warmer than all other years included in the reconstruction is a very different thing than saying this year is warmer than a particular year in the past," he added. "You have to think about the uncertainty in the temperature estimate for each year, and then be able to say that recent years are warmer than all past years simultaneously."
To assess such probabilities, Tingley and Huybers use a statistical model that gives a large ensemble of equally likely temperature histories for the last 600 years, as opposed to the single best estimate provided by most other reconstructions of Earth's temperature. "By sorting through these many plausible realization of what Earth's temperature may have looked like", Huybers said, "it becomes possible to find the probability associated with a great variety of relevant quantities, such as whether the 2010 Russian heat wave was more anomalous than all other events or whether the trend in average temperature over the last 100 years is uniquely
|Contact: Peter Reuell|