As I walked from my house to the train station during last week’s torrential downpour in New York, I found myself in need of a 21^st-century Sir Walter Raleigh (you know, he who spread his cloak over a puddle in 1581 so Queen Elizabeth I would not get her feet wet). A cloak wasn’t going to do it for me, though: the intersection I needed to cross to reach the street climbing up to the station had become a 2-foot-deep lake, judging by where the water reached on cars intrepid enough to try to get through. A garbage can bobbed along in the current. I flagged down a passing car, who drove me around the block rather than through the flood.

This comes to mind on yet another morning of torrential rain in the city because of a new study, to be published later this week in the journal Nature (subscription required). Scientists compared global rainfall records from 1925 to 1999 to various models of precipitation: those that include only natural causes (normal variability in the planet’s climate system and changes due to volcano eruptions, for instance), those that include only human effects (release of greenhouse gases into the atmosphere) and those that include both. Their conclusion: human activity “has had a detectable influence on observed changes in average precipitation,” they write, and these changes “cannot be explained by internal climate variability or natural forcing.” (Natural forcing includes things like changes in solar output as well as volcanoes.) In fact, “the estimated contribution of natural forcing to observed zonal precipitation trends is small in relation to the estimated contribution from anthropogenic [that is, manmade] forcing,” the scientists conclude.