When the gun goes off to start the Boston Marathon on Monday, the temperature is forecast to be in the 50s -- in other words, perfect record-setting weather. But some scientists warn that global warming may one day bring an end to faster times at the world's oldest annual marathon.
"By the year 2100, the average temperature at Boston will have changed enough to affect race times," said Richard Primack, professor of earth and environment at Boston University, who co-authored a study on the topic.
There's one caveat: the data used in the study presumes a starting time of noon, the time at which the marathon began until 2006. The new starting time of 10 a.m. could slightly alter outcomes, although probably not significantly, Primack said.
When the researchers set out to study climate and the marathon, they analyzed a variety of weather factors using data from the Blue Hill Meteorological Observatory from 1933 through 2004: humidity, cloud cover, wind speed and direction. The only two elements that proved to be significant? Wind and temperature. In fact, the potential for a strong tailwind is one reason why times from the point-to-point Boston Marathon don't count as world records: a course has to be a loop, starting and ending at the same point, for an official world record according to International Amateur Athletic Federation.
"Every 10 degrees slows the race by two minutes," Primack said. "So between 2011 when it was relatively cool at 57 degrees and 2012 when it was around 89 degrees, there was a 9-minute difference in winning times."
And that's just the elite runners. It's likely that the rest of the field feels the impact more than the winners.
"It would affect average runners much more, and weaker runners even more dramatically," said Primack, who logged a 3:56 time at Boston on cold, drizzly day in 1970. "If you're exposed for a longer period of time to high temperatures, you're losing more water."
Running coach Jason Karp, author of Running a Marathon for Dummies, agrees.
"The elite runners are only out there for a little over two hours, and others are out there for four or five hours," Karp said. "In a lot of ways it's more stressful to be out there longer. And, the more you're in shape, the better you are at cooling yourself."
Even though the average temperature in Boston has already warmed by about 5 degrees over the past 80 years, Boston weather is so variable that it will take much more of a warming trend to affect the average of one specific day -- in this case, Patriots' Day. The researchers calculate that if temperatures warm at the same speed, there will be a 64 percent chance that winning times will slow. But if the temperatures warm faster, as high as 9.4 degrees as some models predict, that chance rises to 95 percent.
So, what's a Boston-qualified runner to do on a warm day? Karp has a few suggestions:
"The best thing they can do is acclimatize," he said. If possible, do workouts in the temperature predicted for race day for two or three weeks leading up to the marathon.
When that's not feasible, pace your marathon more conservatively than you had planned, and stay as hydrated as possible. Wear white clothes that reflect the sun, made from breathable fabric.
"A lot of people still go out at [their original] race pace on a hot day, and you're going to suffer," Karp said. "Heat will play a factor."
Of course, race organizers could tinker with the race to foster faster times by changing the starting time again, or shifting the race to February or March.
Still, while distance times might slow, sprinters likely won't mind: Cool weather tightens muscles; heat helps facilitate the intense muscle contractions involved in sprinting.
"Sprinters love temperatures in the 80s," Karp said.