As scientists across the world research climate change, Williamsburg’s relatively milder winters and warmer summers during the past three years might not be a sign of impending climate change so much as a return to normal, according to a College of William and Mary weather researcher.
At the Keck Environmental Field Laboratory at Lake Matoaka in Williamsburg, data shows the past three winters and summers have been relatively warmer than normal.
The average temperature for Williamsburg since 2004 has been about 59 degrees Fahrenheit, but in the past three years that temperature has been about 1.25 degrees higher.
Since 2004, Williamsburg has seen a decline in the number of degree heating days — the days where it’s generally colder than 65 degrees Fahrenheit, according to the National Oceanic and Atmospheric Administration. There also has been a corresponding increase in the average number of degree cooling days in the past three years compared to the average since 2004.
At 1,063, 2018 had the second-highest number of degree cooling days in the past 15 years, according to William and Mary professor Randy Chambers. 2010 had the highest number of degree cooling days at 1068.
Simply put, degree days are a measure of the amount of energy it takes to make a living space comfortable. Changes in the number of degree days can be used to see the tangible differences people experience due to changes in weather and climate.
If the average temperature for a day is 0 degrees Fahrenheit, that would lead to 65 degree heating days because it would require an additional 65 degrees Fahrenheit of heat to make the temperature comfortable. The more degree days there are, the more it costs to heat or cool homes or offices.
Williamsburg’s milder winters might not be a departure from the norm due to climate change so much as a return to the norm after regional weather patterns affected the area for several years, Chambers said.
“Interestingly, the combination of cold winters and mild summers last occurred in 2013 and 2014, so the recent warming trend in 2016-2018 is probably not an indication of climate change per se, but rather an outcome of regional circulation patterns, responses to El Nino events, etc.,” Chambers wrote in an email.
“Some years are hot, some are cold, but the combination of mild winters and hot summers has happened only four of the last 15 years, and three of those years are 2016-2018.”
The Keck Lab’s data doesn’t go back far enough to determine long-term trends at this point — it dates to 2004 — but while the hyper-local weather station continues to collect data, the federal government has issued dire warnings about climate change’s effects on Virginia.
The lab doesn’t make forward-looking projections. Instead, it retains the weather data in-house and transmits it to Weather Underground, a company that provides weather information to the public.
Since 1900 there has been a marked increase in the number of extreme rainfall events and observed higher summer temperatures in Virginia, according to the Fourth National Climate Assessment.
Published in two volumes between October 2017 and November 2018 by the federal government, the assessment provides information on the threats the United States faces from climate change in the coming century. The first assessment was published in 2000 by the U.S. Global Change Research Program.
As Virginia looks to climate pattern predictions in the coming century, the future looks bleak.
The assessment predicts more intense droughts, a 5 to 10 percent increase in annual rainfall by the middle of the century and increased flood risks as sea levels are expected to rise worldwide by 1-4 feet, depending on greenhouse gas emissions.
Weather extremes will take their toll on the landscape, the assessment warns. For example, even though there’s expected to be more rainfall in the coming century, less of the rain that falls will filter into the ground due to higher temperatures that will cause the rain to evaporate faster. That could lead to more intense flooding coupled with more intense droughts.
Climate change will be somewhat dependent on greenhouse gas emissions — reductions of emissions could lead to less drastic climate change, according to the assessment.
However, even with reductions, the assessment said, Virginia will likely be even hotter by 2100 — at least 2 degrees fahrenheit or as much as 13 degrees.
Roberts can be reached at 757-604-1329, by email at firstname.lastname@example.org and on Twitter @SPRobertsJr.