Every year, runners getting set for the Miami Marathon and Half Marathon study the weather forecast with trepidation. They expect to sweat a lot during the subtropical endurance test, but they hope for mild temperatures just before dawn at the starting line, then plead with the sun rising along Miami Beach to bask them in gentle or better yet obscured rays rather than beat them with scorching ones.
Favorable conditions in the low 50s are predicted for Sunday. But if local and global warming trends continue, marathon finish times will eventually suffer. As the world heats up, runners will slow down.
The optimum temperature range for optimum performance in the 26.2-mile marathon is 45-50 degrees, numerous physiological studies have shown. A hotter earth decades down the road means runners could hit another type of wall in the future — one dictated by the thermometer.
As the world’s best marathoners approach the two-hour barrier, scientists are contemplating when fast times will intersect with temperatures that will diminish pace.
Miami is unlikely to ever be known as an incubator of elite marathoners because of its abundance of heat and humidity and lack of hills. But the Miami Marathon and Half Marathon has not only found a comfortable niche as a destination event but also the ideal window in which to hold it in late January or early February. Since its inception in 2003, the average temperature at the 6:15 a.m. start has been 65 degrees, with an average temperature four hours later of 72 degrees. Average humidity at the start has been 83 percent, which typically drops with each hour of the race. There have been brutal years, such as 2007 and 2014, when it was 72 at the gun and 80 by the time many runners crossed the finish line, but Miami has avoided dangerous extreme conditions, such as those at the 2007 Chicago Marathon and 2012 Boston Marathon, when temperatures rose to the high 80s.
While the conditions on race day will always vary, Miami’s climate is changing along with the rest of the world. Last year was the hottest on Earth by the widest margin since record-keeping began in 1880 as well as the hottest on record for South Florida, with an average temperature of 79.2 degrees in Miami, according to the National Weather Service Forecast Office and the National Oceanic and Atmospheric Administration. Three of the past four winters have been warmer than normal. A temperature of 100 degrees was recorded for the first time in the month of April at a South Florida site — the Royal Palm Ranger Station in the Everglades.
“What we’ve seen here is mirroring the global trend of increasing temperatures,” NWS meteorologist Rob Molleda said. “December was a hot anomaly here and across the country. We’ve settled into January, our coolest and driest month and certainly the right time to increase your odds for a chilly marathon.”
Frankie Ruiz has been running in Miami all his life and concedes that the climate is a disadvantage for distance runners. The only U.S. Olympic marathoner who lived in the area was Keith Brantly, and he did much of his training in North Carolina.
Ruiz, who is Chief Running Officer for Life Time Fitness, which owns the marathon, and coach of perennial prep cross-country and track powerhouse Belen, has noticed changes in the weather.
“I feel like it’s staying warmer longer,” he said.
“Our Coconut Grove training group didn’t have its first mild run until week 20 in the program. And I felt guilty buying Belen warmup suits because I knew they’d never wear them. We’ve adjusted by making earlier or later start times for workouts, and we do more on the treadmill, in the pool or in the parking garages, out of the sun.”
Endurance performance is impaired by warm temperatures because about 80 percent of the energy required for a marathon is transferred as heat to the body’s core. That heat must be dissipated, which is more difficult in hot and humid air.
“Air temperature is the most important factor influencing marathon running performance for all levels,” concluded a study entitled “Impact of Environmental Parameters on Marathon Running Performance” that compared results of six U.S. and European marathons with a total of 1.8 million participants over the course of nine years.
The correlation between speed and temperature was consistent, said lead author Nour El Helou. Finishing times in the unusually warm 2007 London Marathon starting at 66 degrees were on average 17 minutes slower than times when the temperature was close to the normal 52 degrees.
Humidity is our nemesis. It becomes tougher and tougher for the body to self-cool in South Florida weather. You either adapt or you move to a colder place.
Elite marathoners’ times slowed up to 4.5 percent and average marathoners’ times slowed up to 8 percent as temperatures increased from 42 to 77 degrees, according to a study of seven U.S. marathons — including Boston and New York — in the Medicine and Science in Sports and Exercise journal by lead author Matthew R. Ely.
Slower runners experience larger declines because they are exposed to warming conditions longer and because their fitness levels make it harder to cope with heat stress.
The study also found that running in a pack causes three times the heat stress as running solo because of the increase in ambient temperature and decrease in heat dissipation.
Researchers found such examples as a person who runs an eight-minute-mile pace at 50 degrees slowing to 8:40 at 70 degrees or 9:06 at 80 degrees. A 4:30 marathoner at 40 degrees could slow to 5:06 at 70 degrees. Every five-degree increase above 60 degrees can slow pace by as much as 20-30 seconds per mile.
A Boston University study showed that winning times in the Boston Marathon will slow down if Boston’s climate continues to warm.
If temperatures increase by the mid-range global warming estimate of 4.5 degrees, there is a 64 percent chance times will be slower by 2100, and if the shift is at the high range of 9.4 degrees, there’s a 95 percent chance of slower times by the end of the century, the authors found.
They said the winning time was almost two minutes slower for every 10-degree increase. For example, the men’s winning time in 2012, when it was 89 degrees, was nine minutes slower than in 2011, when it was 57 degrees.
Miami Beach runner and triathlete Michael Mandich foresees Sunday’s mild temperatures as a reward for local athletes.
“The fall was stifling, and I remember even back in April the run portion of the South Beach triathlon was horrible in blazing heat,” said Mandich, CEO of the Dolphins Cancer Challenge and son of the late former Miami Dolphin Jim Mandich. “On the other hand, when it was cool last winter I ran some of my best times — a 1:25 in the Miami Half Marathon and a 3:04 in the Fort Lauderdale Marathon.
“Humidity is our nemesis. It becomes tougher and tougher for the body to self-cool in South Florida weather. You either adapt or you move to a colder place.”
Ruiz has noticed more warmth during Belen’s summer training camp trips to North Carolina, Colorado and Oregon. Hot fall training conditions here mean Florida prep teams usually finish at the bottom at Nike’s high school cross-country national meet in Portland, Oregon.
As temperatures rise, he’d like to see Miami become more of a track and field hotbed — and he’s advocating for more water fountains along popular running routes.
But he’s confident the Miami Marathon and Half Marathon will continue to attract runners happy to trade cold temperatures for the sight of palm trees and porpoises.
“We start very early, we have lots of shade, and the majority of our entrants come from Florida, the Caribbean or Latin America, so they are acclimatized,” he said. “As it gets hotter, they’ll get more resilient.”
Weather for Miami Marathon and Half Marathon
humidity at 6 a.m.
humidity at 10 a.m.
66 degrees/90 %
From the National Climatic Data Center, Miami International Airport site