Sunday, March 25, 2012

Spring, 2012: Just A Fluke, or A Taste of the Future?

Partial ice-out on Lower Saint Regis Lake , March 22, 2012.

Record-high March temperatures have driven the ice from Lower Saint Regis Lake earlier than usual.  Only about half of it remains today (March 25), all rotten and waiting for a final push by the wind to disintegrate completely.  Several climatic factors have conspired in this, including La NiƱa, the Arctic Oscillation, and snow-free ground that the sun is warming faster than it would if it the land were covered with reflective whiteness.  But the heat wave and early ice-out also fit a larger pattern of change in the North Country. 

According to records kept by faculty and staff at Paul Smith's College, this ice-out came earlier than at any time in the last 4 decades (see the dot in the far lower right corner of the chart below).  But it wasn't completely out of the blue, either.   It fits into a decadal-scale trend of earlier ice-outs, as well. 

For most of the last century, the largest changes in North Country ice cover have been in the later and later timing of freeze-up dates.  Nowadays the main basin of Lake Champlain often fails to ice over at all in winter.  A trend toward earlier ice-out dates on local lakes has been weaker, partly because variable snow cover and wind action complicate the picture in spring, but also because our spring temperatures haven't warmed as consistently as autumn temperatures have during the last century or so. (link to report on climate change in the Champlain Basin)

Until recently, that is.  For the last 2 decades, spring temperatures in the North Country have risen more consistently, and in 2010 the ice-out trend on Lower Saint Regis Lake became statistically significant.  This year's super-early melt-off strengthens the trend even more.

So yes, our mid-March heat wave was unusual and it was not all due to greenhouse warming alone.  But I think it would be a mistake to leave global change out of the picture altogether.  This spring is not just a meaningless random anomaly.  As you can see for yourself on the chart above, it's where we've been headed for quite some time.

Spring 2012 may not be a new normal - yet.  But with heat-trapping fossil fuel emissions continuing to accumulate in the atmosphere, it seems like a reasonable bet that future springs will begin to resemble this one more and more as the world continues to warm.