Warming trend continues with spring temperatures in New England

This article originally appeared in the June 12, 2012 issue of the Daily Hampshire Gazette.

AMHERST—For Boston, Hartford and Worcester, this spring was the warmest on record, according to Michael Rawlins, the manager of the climate research center at the University of Massachusetts Amherst. For Amherst, it was the second warmest.

This is representative of a long-term trend of increasingly warm spring temperatures that is consistent with an increase in greenhouse gases, according to Rawlins. But that doesn't necessarily mean that this is climate change.

"It is not that simple," said Alan Werner, a geology professor at Mount Holyoke College. "It may be, but not necessarily."

The new records are not staggeringly different from previous ones, edging out old records by tenths of a degree.

Boston recorded a mean temperature of 53.4 degrees Fahrenheit from March through May, a 0.2 degree difference from the previous record set in 2010. Hartford averaged 54.3 degrees, tying the 2010 record and beating the 1991 record by 1.1 degrees. Worcester exceeded its previous record of 51 degrees by 0.3.

Amherst's mean temperature of 51.4 degrees was 0.7 less than the previous record set in 1991.

"The fact that this was a tenth or a few tenth degrees warmer is not tremendously impactful," said Rawlins.

But, according to Rawlins, the trend of increasingly warm springs could be significant, noting that if the average spring temperatures for the last 100 years are plotted on a graph, the points would show a gradual increase in temperature.

"There has been a long-term trend in spring temperatures over the past several decades that have impacts for crops, fish habitats and so on," said Rawlins. "Some of the impacts are beneficial, but there are also some potentially negative influences over time from global warming."

The International Panel on Climate Change, an organization of over 1,300 climate scientists from 195 nations, predicts that climate change could cause more heat waves in cities that already experience them, snow loss in the mountains and a 5 to 20 percent increase in the yields of rain-fed agriculture.

According to records kept over a varying span of years by each municipality, the average spring temperature is 48.9 degrees in Hartford, 48.1 degrees in Boston, 45.7 degrees in Worcester and 46.0 degrees in Amherst.

For Boston, Hartford and Worcester, this is the second year in a three-year period that spring temperatures have broken records.

"It makes you sit up," said Werner.

But, Werner, a paleoclimatologist who studies climate that predates the historical record, is quick to point out that warm temperatures don't necessarily mean climate change and that cold temperatures don't necessarily mean that climate change isn't happening.

"It is important to understand that weather still happens despite climate change," Werner said.

Scientists draw a distinction between weather and climate. Weather is the day-to-day unpredictability of what is happening outside. Climate is the long-term averages of these day-to-day events.

Several factors may have contributed to the warm weather this spring, said Rawlins.

The polar jet stream, a cold air current that usually flows through Canada and sinks into the northern United States for the winter, never sank this winter, causing the winter and spring to be unseasonably warm, according to Alan Dunham, a meteorologist at the National Weather Service in Taunton.

"Instead of air from Canada, this year the air came from the southern United States," said Dunham.

The temperatures also could have been influenced by La Niña, a weather pattern in the Pacific Ocean that can cause unpredictable weather in South America and primarily the southern United States, according to Rawlins. It also could have influenced weather in this region, he said.

Dunham attributes the warm spring to weather variability. "There are just some years that are warmer," he said.

Rawlins and Werner are not as quick to judge.

"It makes people crazy," said Werner. "They want to know if this is climate change or weather, but it is not that easy."

"You have to be careful of over-interpreting the data, but on the other hand we are seeing a trend," he said.

The Climate System Research Center predicts an equal chance of the next three months being below average, average or above average in the Northeast, according to Rawlins. The predictions are based upon the surface temperature of the ocean, soil moisture and long-term seasonal trends.

"These forecasts have much less skill than a three- or five-day weather forecast," he said.