ORONO, Maine — Yes, a state record was set this winter when a temperature of 50 degrees below zero was recorded Jan. 16 in Aroostook County.
That doesn’t mean the phenomenon of global warming has slowed or stopped, said Martin Hoerling, a meteorologist at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo., as has been suggested in popular books and by politicians.
“The climate system isn’t moving along a smooth curve,” Hoerling said Thursday morning in the University of Maine’s Barrows Hall during his keynote address to the 17th annual Harold W. Borns Jr. Symposium. “There’s variability … and by and large this variability is due to natural ocean atmospheric fluctuations from one year to the next.”
The two-day symposium, held in Arthur St. John Hill Auditorium, brings together dozens of faculty members and graduate students affiliated with UMaine’s Climate Change Institute to give presentations on their research. Presenters come from disciplines including biology, earth sciences, history, computer sciences, archae-ology and anthropology, said George Jacobson, a professor of quaternary biology and former Climate Change Institute director.
Hoerling also serves as chairman of the U.S. Climate Variability and Predictability Program, known as CLIMAR, which is part of the World Climate Research Program.
Hoerling said data show that after 30-40 years of warming, temperatures seemed to have plateaued rather than continued to rise since 1998, and that 2008 was one of the coldest years in very recent history. Some people have drawn the conclusion that global warming is over, he added, or that the scientists’ models and measure-ment tools were flawed.
One could point to the Jan. 16 record as proof that global warming has stopped, Hoerling said, but one day, year and decade aren’t enough to prove a trend.
Hoerling said data show the current rate of warming is unusual in the context of the last millennium. At the same time, he said, the amount of carbon dioxide in the air has increased by 80 parts per million in the last 100 years. That level of buildup compares to a similar rise that took 5,000 years after the ice age.
The central idea of Hoerling’s address — that occasional highs and lows such as the January record are anomalies in the big picture — is one that also is key to the Climate Change Institute’s work. In fact, some of the data Hoerling cited in his talk came from UMaine research, Jacobson said.
“By having this knowledge of what the natural variability is, we can see that, well, the only way this would be happening is by adding the greenhouse gases,” Jacobson said. “The recent additions from humans are the only way we can explain the last 30 or 40 years of warming. Climate is so complicated and there’s so much vari-ability.”
Contrast the record cold day in January, Jacobson added, with a record warm day April 25, when the temperature hit 77 degrees in Caribou.
Hoerling said events such as the symposium are critical to helping broaden the understanding of climate change.
“It’s the sweep of history that’s so compelling in telling our story about how we understand the climate system,” Hoerling said. “It’s [with] that depth of understanding that we build our credibility for the types of interactions that we are having as a community with the public and the policymakers.”