The winter solstice marks the shortest day of the year, when the sun is at its lowest point in the sky in the Northern Hemisphere.

Five cities in the northeastern United States broke their own record of all-time hottest year in 2010, according to a report out Wednesday (Jan. 5).

For Boston, 2010 had the highest average temperature since records began being kept in 1872, when The Great Fire almost wiped the city off the map. The other four cities were: Providence, R.I.; Hartford, Conn.; Concord, N.H.; and Caribou, Maine.

The findings come from statistics released by the Northeast Regional Climate Center at Cornell University.

The researchers looked at temperature data collected by the National Oceanic and Atmospheric Administration (NOAA) at various sites in cities across the northeastern United States. The yearly number for each city is the average of daily temperatures, which themselves are an average of the day's minimum and maximum temperature. [Infographic: Hot Spots in 2010]

Then they compared each number with the historical record based on similar thermometer readings from those stations.

"This year in general was warm, not just at a single station, but it was warm across a range of stations in the region," said study researcher Art DeGaetano, a climatologist at Cornell.

For instance, 23 of the 35 cities monitored saw the average temperature for 2010 rank among the 10 hottest years on record. The only cool spots, ranking mid-pack by historical standards, were along the Appalachian Mountains from Charleston, W.V., which ranked 60 out of a 106-year record, to Pittsburgh, Pa. (ranking 68 out of 136 recorded years).

At John F. Kennedy Airport in New York City, 2010 was the second-hottest year since records began being kept a half-century ago. And temperatures along the boardwalk at Atlantic City, N.J., hit their second-highest mark in more than 130 years of record-keeping.

None of the cities monitored set a record low average temperature in 2010.

Why the warm year? "I can't tell you one thing that has caused this year to be warmer than any year in the past 100 years. It is a combination of things," DeGaetano told LiveScience, adding that several atmospheric patterns may have contributed. "It's also likely to be the trend toward warmer temperatures that most people attribute to global warming."

Whatever the cause, the northeast may be reflecting a global trend. "If you look at some of the preliminary data that has come out for the globe it looks like 2010 will be, if not the warmest, one of the warmest years globally," DeGaetano said.

You can follow LiveScience Managing Editor Jeanna Bryner on Twitter @jeannabryner.