New York ( CNN ) -- As weekend temperatures soared over 90 degrees Fahrenheit , New York City saw a sudden increase in shootings , with 26 people felled by bullets in 72 hours -- seven fatally . `` When we have hot temperatures , we see that the crime rate seems to go up , '' New York City Mayor Michael Bloomberg said Monday . But Bloomberg emphasized that for the year , shootings are down in the city -- 127 since January 1 , which is 40 less than the same period in 2012 . `` One shooting is one too many , but last week we had the fewest shootings in a decade , including this weekend 's shootings , '' Bloomberg noted . A professor says the heat index and the crime rate can connect . `` Lifestyle differences exist between cold weather and warm weather , '' says James Alan Fox , a professor of Criminology , Law and Public Policy at Northeastern University in Boston . Fox has conducted research on the possible connection between temperature and crime . His findings illustrate how these lifestyle differences can contribute to varying levels of violent crime . `` In cold weather , particularly in blizzards , people stay indoors , and the violent crime rate is lower . When the weather is warm , people are interacting more with others , be they friends , family , or strangers , so there are increased opportunities for conflict , '' Fox says . Fox says this trend continues except when it gets incredibly hot , so unbearable that even criminals become lethargic . `` When it gets to be in the high 90s , especially over 100 degrees , people just go indoors and look for air conditioning , '' Fox said . However , drawing any conclusions about this past weekend may be premature , says Professor Jon M. Shane , assistant professor in the Department of Law , Police Science , and Criminal Justice Administration at John Jay Criminal College . `` I would not put too much emphasis on a single spike in weather and the uptick shootings , '' Shane said . `` The reality is that you do not have enough information from this single episode to conclude that hot weather is related to increases in crime -- specifically shootings , in this case . '' In November 2012 , New York City logged a record-breaking `` murder-free Monday '' when there was not a single reported slaying , stabbing , shooting or knifing in any of the five boroughs , according to the New York Police Department . `` It is unusual in a city of 8 million people , but we never read that much into one day , '' said Deputy Police Commissioner Paul Browne , who said it was the `` first time in memory '' that the city had such a lull in violent crime . At the close of 2012 , Bloomberg hailed New York City the `` safest big city in America , '' giving the NYPD credit . `` The fact that the safest big city in America is safer than ever is a testament to the hard work and determination of the men and women who put their lives on the line for us every day -- and it also reflects our commitment to doing everything possible to stop gun violence , '' Bloomberg said . CNN 's Chris Boyette and Adam Reiss contributed to this report .
Bloomberg : `` When we have hot temperatures ... the crime rate seems to go up '' But year-to-date , shootings are down in New York City . A professor explains : `` Lifestyle differences exist between cold ... and warm weather '' Another professor says there 's not enough evidence to blame weekend numbers on heat .