Boston's hurricane history: Eight fierce storms in the 13th century

By Beth Daley, Globe Staff

It remains a key question in climate change science: Will hurricanes become fiercer and more frequent as the world warms?

Scientists know that hurricanes draw their strength from warm seawater, so even small changes in temperature can give a storm much more energy, increasing its fury. But while there has been a notable increase in hurricane activity since 1995, it’s not entirely clear if it is part of a natural cycle or because ocean sea surface temperatures have warmed from the release of heat-trapping gases from cars, power plants and factories.

Learning about these... (NOAA picture)

Part of the problem, it turns out, is that scientists don’t have great records of hurricane activity in the past. Aircraft reconnaissance of storms started in the 1940s and satellite observations used today began in the 1960s. The instrumental record, which goes back about 130 years, is spotty.

But Mark Besonen, a University of Massachusetts Amherst post-doctoral researcher has been able to peer back in hurricane history to 1011 A.D – in Greater Boston.

Besonen examined layers of lake sediment that, just like tree rings, left an annual record in the Lower Mystic Lake that straddles Medford and Arlington.

...From the Lower Mystic Lake (Globe photo)

Hurricane strikes often causes vegetation disturbances and tree blow-downs which exposes lots of fresh, loose sediment. So he painstakingly looked through the lake’s layers for that coarser sediment to identify intense hurricanes.

The number of hurricanes striking the Boston area was lower in the 11th century and the 17th to 19th centuries, with higher activity in the 12th-16th centuries, he found. Overall, the frequency of hurricanes striking the Boston area varied widely over the last millennium with periods of lowest activity corresponding to cooler sea surface temperatures in the tropical North Atlantic. During some centuries, Boston only received one to three intense hurricanes. At other times, such as in the 13th century, the area had as many as eight.

The findings don’t help answer if climate change is causing more hurricanes but it will help scientists. Besonen’s work will likely help computer climate modelers perfect their techniques. They will try to reproduce the past hurricane record and if they can, they will have more confidence in projections of future changes.

“By studying how (hurricanes) has varied naturally in the past, we can better understand the underlying factors that affect hurricane development,” Besonen said.

Besonen’s results were published last month in Geophysical Research Letters. UMass professor Ray Bradley and three other scientists contributed to the work.