We’ve already seen how ice-out on the Tanana River in Alaska has been trending earlier in the year. We’ve also seen a lame attempt at WUWT to suggest that it’s because of anything but warming temperatures. Ooh ooh — is it the Pacific Decadal Oscillation? Uh, is it urban heat island effect from the giant city of Fairbanks, Alaska 40 miles away? No it isn’t. What could it be? Hmmm, could it be … Satan?
Since the subject came up, let’s look at some more ice-out data — from a part of the U.S. quite far from Alaska. The U.S. Geological Survey in Maine has ice-out dates for New England lakes. 29 lakes, in fact, with data from as early as 1807 up to 2005. Let’s take a look.
The overall trend in ice-out day is quite similar for all these lakes. Compare, for instance, the record for Cobbosseecontee Lake:
to that for Damariscotta Lake:
Not just the overall trend, but the year-to-year fluctuations are quite similar. That’s because the changes in ice-out day are primarily due to warming temperature.
Of course these data only go up to 2005. But I doubt there’s been a sudden reversal of the trend, especially since the Portland Press-Herald reported on March 23, 2010, that “A Maine lake has been declared ice-free earlier in the season than any other year in 136 years of record-keeping,” referring to Maine’s Lake Auburn. If the paper reported ice-out on March 23rd, it must have happened by March 22nd, which is day 81 — considerably earlier even than what would be expected from the receding trend which was already obvious by 2005:
We can even compare the smoothed curves for all 29 lakes on one graph:
Most of the lakes have an average ice-out day later than day 90, but two of them tend to thaw earlier. They’re from the more southern part of New England, Houghton’s Pond and Ponkapoag Pond in Massachusetts. We can also take a closer look at the 27 other lakes:
What conclusion is blatantly obvious from this? Hmmm…
Of course, we can fit a linear trend line to the data for each lake. This is an imperfect way to characterize the trend, because clearly the trends are not linear, but at least it will give an overview of the general “consensus” of New England lake data. Out of 29 lakes, 27 show a negative linear trend in ice-out day while only 2 show a positive linear trend. But the 2 positive trend rates fail statistical significance (not even close) — it’s more descriptive to say that out of 29 lakes, 17 show a statistically significant negative trend (earlier ice-out) and 12 show no significant trend.
And why, you wonder, is the ice breaking up earlier on New England lakes? Hmmm …