December 13, 2012
Winters Will Be Warmer And Wetter In The Northeast By 2070
April Flowers for redOrbit.com - Your Universe Online
A team of climate scientists from the University of Massachusetts Amherst has released a new study suggesting temperatures are going to be significantly warmer in all seasons in the next 30 years, especially in winter.
The study, published in the current issue of the Journal of Geophysical Research, is the first to apply regional climate models to examine likely near-term changes in temperature and precipitation across the Northeast United States. Along with warmer temperatures, the study projects that winters will be wetter, with more rain likely than snow.
The UMass team, along with Henry Diaz of NOAA's Climate Diagnostics Center, provides the highest resolution climate projections available to date for the Northeast — ranging from Pennsylvania to Maine — for the period 2041 to 2070, using data from multiple climate model simulations run at greatly improved resolution.
Michael Rawlins, of the Climate System Research Center at UMass, says, "One of the most important aspects of our study is that we can now examine in more detail what's likely to occur across the region with a grid size of approximately 31 x 31 miles (50 x 50 km). Previous studies used much more coarse-scale general circulation model data. This represents a significant step forward."
His colleague, Raymond Bradley, adds, "Regional climate models have been around for a while, but they have not been applied specifically to the Northeast region. At this point what we can provide are 'broad brush' estimates of how things will change over the next 30 to 50 years. People should not over-interpret these results. Further research is needed to scale these down to individual locations. But for natural resource conservation managers, water resource managers and others responsible for planning ahead, we expect our region-specific results will be helpful."
By mid century, the research team expects the entire region to warm by some 3.6 to 5.4 degrees Fahrenheit. Local changes may approach as much as 6.3 degrees warmer in winter. They also predict an increase in precipitation, especially in winter, but not uniformly across the region. Confidence in the precipitation change projections for spring, summer and autumn is lower, the team says, given smaller changes relative to natural weather variability.
"The only clear signal of change for precipitation is noted in winter, which appears to be heading toward wetter conditions, consistent with current trends," Rawlins says.
The projections for winter precipitation show a significant rise above natural weather variability, around 12 to 15 percent greater from southwest Pennsylvania to northern Maine. The exceptions are in the coastal areas where projected increases are lower.
"But we shouldn't expect more total seasonal snowfall," he adds. "Combined with the model-projected temperature trends, much of the increase will occur as rain. We're losing the snow season. It is contracting, with more rain in early and late winter."
The team used available outputs from an ensemble of regional climate models (RCM) from the North American Regional Climate Change Assessment Program (NARCCAP) to guage potential changes in air temperature and precipitation on a seasonal basis between the present — 1971 to 2000 — and the future — 2041 to 2070. By comparing its outputs to actual weather station data, the team performed a rigorous evaluation of each model's ability to represent current climate.
Greenhouse gas emissions will continue to rise, the predictions assume, increasing atmospheric CO2 from about 400 parts per million (ppm) today to between 500 and 600 ppm in 2070. The team says for CO2 levels, this outlook represents "most aggressive, most troubling higher emissions trajectory scenario." They point out that there is little evidence so far that society will act to change the current rate of increase in any appreciable manner.
Data from two general circulation models (GCM) were used to force each of the five RCMs resulting in nine GCM-RCM simulations, providing a rich suite of data for climate change analysis. Much higher-resolution depictions of precipitation and air temperature are made possible by applying GCM forcings at the boundaries of the North American region with RCMs then taking over.
The results of this study reveal statistically significant increases in air temperature region-wide for every grid in each season. The changes, however, are not uniform. Models collectively project air temperature changes in winter of more than 5.4 degrees F across northern Maine, all of New Hampshire, Vermont and the Adirondacks, for example. This represents about 50 percent of the Northeast region. In local areas, the increase could be nearly 7.2 degrees F.
Winter air temperature increases in southwest Pennsylvania, in contrast, are projected to be lower, only about 4.3 degrees F. The pattern is reversed in summer, with the southwest quadrant of the northeast projected to be warmer and the changes higher.