Snow in the new era

Those 20 and under might well have a very different view of the Philadelphia winter from that of their elders.

All four of the biggest snows in Philadelphia have occurred since 1996, three of those since 2009.

Tens of millions of dollars in Federal Emergency Management Agency disaster aid is about to descend on New Jersey and Pennsylvania for the Jan. 22-23 blizzard cleanup.

Officially, that one was No. 4 in Philadelphia, with an official 22.4 inches, and it drew the first federal disaster declaration since the record-holding Jan. 7-8, 1996 storm credited with 30.7 inches.

Given the recent trend – and from 1885 to 1983 Philadelphia had experienced only one snowfall of 20 inches or more;  not a single snowfall of 8 inches or more occurred between February 1967 and January 1978 -- might we be seeing more disaster declarations around here in the winters to come?

That might well happen.

First, a disclaimer: For any number of reasons, U.S. disaster assistance is an absolutely terrible barometer of climate trends.

But the steroidal increase in snow totals in the Northeast has drawn attention in the climate community.

Jennifer Francis at Rutgers and others have speculated that Arctic melting, which has led to a harvest of free-flowing water near the top of the world might be affecting atmospheric patterns in such a way as to precipitate juicier winter storms.

One of the hot new areas in climate-change research is "attribution," in simple terms the process of trying to tease out the human influence in weather events.

No responsible scientist would say that a given storm was "caused" by global warming. They are more apt to speak in terms of how warming increases the probability of certain "extreme" weather.

That background warming contributes to heat waves; sea-level rise, and extreme precipitation events, and nuisance flooding are well-established.

Hurricanes, tornados, mega-snowstorms and other complex phenomenon tied to local conditions are another matter.

Perhaps paradoxically, natural variability is a constant in everything that happens in the atmosphere. Various researchers are trying to get at the perturbing effects of the human contribution.

We have been reading through a report published by the National Academy of Sciences on this subject that we highly recommend.

We are loathe to use the terms "denier" and "alarmist," lest they tar responsible, thoughtful people who are trying to get to the bottom of all this, but we'll say some are likely to say that it goes too far and others that it's doesn't go far enough.

In any event, we are confident that we've seen the last of winter-storm disaster declarations, at least until next winter.