Fall warming: The case of the lingering colors
Record-threatening highs due this week, and a trend continues.
At least one Philadelphia high-temperature record should fall this week as warm air surges into the East, and halfway through the meteorological fall, this one is looking familiar.
In the last 25 years, the September through November official temperature in Philadelphia has averaged 1.6 degrees above the average for the previous 117 years in the period of record.
What happens locally doesn't necessarily parallel what's going on elsewhere in the planet, but Philadelphia's figures track decently with worldwide warming trends.
What's more, the appearance of the first freeze – which we define as the first occurrence of 32-degree temperature at Philadelphia International Airport – has been occurring later.
How this trend is affecting the annual fall-foliage shows remains a source of speculation and research.
Marc Abrams, the Penn State foliage specialist, notes that the colors seem to be arriving a tad late this year, and we would second that from what we've seen around here.
But fall colors are primarily about light, which would change infinitesimally from season-to-season with ultra-subtle changes in the sun's orbit that only astronomers would understand.
One thing is evident: The color seasons are lasting longer.
As Paul Meyer, head of the Morris Arboretum has pointed out, that has something to do with the proliferation of exotic tree species.
But it also has something to do with the warmth's role in delaying leaf-fall.
Unfortunately, we don't know of a well-monitored database that tracks onset and peaks of fall colors.
One of the most-detailed records we've seen is kept by the people who run Polly's Pancakes, in Sugar Hill, N.H., a mighty popular tourist destination up that way where keeping track of foliage is vital part of business.
Their chart, which dates to 1975 and now is in it's fifth decade, shows that while onset and peak times haven't varied much, seasons have been hanging on an average of about five days longer.
Abrams says the overall warming and associated heavier precipitation might be having another positive impact by adding a splash of color.
In any event, the leaves are most definitely starting to change in the region, and we can predict confidently that the best is yet to come.