It is not in doubt that flight seasons are now significantly earlier than they were 50 or 60 years ago. The conventional explanation is global warming. That undoubtedly is likely to be a factor but I offer an additional hypothetical cause.
This spring has not been especially warm yet butterflies have been emerging according to 21st century timetables. I posted on another forum that I had seen whites at 7.5C and Speckled Woods at 8.0C. On those occasions, despite the air temperature, the May sun was very bright.
Guy Padfield has regularly reported active butterflies in mid-winter in Switzerland. The sunshine is brighter there compared British Isles due to lower latitude and no doubt better air quality.
Speculation: could our British earlier flight season be in part due to the improved air quality since various clean air acts/initiatives?
Jack
Earlier butterfly seasons
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Jack Harrison
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Re: Earlier butterfly seasons
I don't know whether cleaner air could precipitate earlier butterfly emergences, Jack, but things have changed markedly even in my lifetime as far as the spring season is concerned.
Apart from a couple of very cold years, things seem to habitually get going in the second half of February now. By that I mean the mass emergence of the spring bulbs, celandines, etc, and, of course, the first butterflies.
Similarly, at the other end of the spectrum, autumn seems to begin during the second half of August, with vegetation looking very wilted and 'tired' by then.
Where I see the greatest change (in this country at least) is the period between late October and early December. When I was younger, this period was generally cold and grim, whereas for the last few years we seem to be having 14-17c temperatures through early November and 12 and 13c even in early December. Who knows, at this rate the Wall Brown may actually become commoner as its third brood strategy eventually pays dividends!
Apart from a couple of very cold years, things seem to habitually get going in the second half of February now. By that I mean the mass emergence of the spring bulbs, celandines, etc, and, of course, the first butterflies.
Similarly, at the other end of the spectrum, autumn seems to begin during the second half of August, with vegetation looking very wilted and 'tired' by then.
Where I see the greatest change (in this country at least) is the period between late October and early December. When I was younger, this period was generally cold and grim, whereas for the last few years we seem to be having 14-17c temperatures through early November and 12 and 13c even in early December. Who knows, at this rate the Wall Brown may actually become commoner as its third brood strategy eventually pays dividends!
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NickMorgan
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Re: Earlier butterfly seasons
It would be very interesting to see some temperature statistics for the last 50 years or so.
Certainly, as I child I remember long frosty spells here in Southern Scotland and it always snowed in winter.
When I moved to Haddington in the mid '80s, my apple trees used to regularly be hit by a hard May frost causing them to drop their flowers and a poor crop resulted.
My eldest son is now 20 and I remember worrying that he may never experience proper snow. For the first ten years of his life we had very mild winters until I think it was 2010 and 2011 when we had a lot of snow. Since then, though, we have barely had any snow here. And the last few winters the night time temperature has hovered around zero, but not much below.
We are about to move to the Scottish Borders. about 30 miles south, 100 metres higher in altitude and a couple of degrees cooler in winter. The apple blossom there has only just come out, but up in Haddington it has been out for four weeks. So, just a small change in temperature appears to make a massive difference.
Certainly, as I child I remember long frosty spells here in Southern Scotland and it always snowed in winter.
When I moved to Haddington in the mid '80s, my apple trees used to regularly be hit by a hard May frost causing them to drop their flowers and a poor crop resulted.
My eldest son is now 20 and I remember worrying that he may never experience proper snow. For the first ten years of his life we had very mild winters until I think it was 2010 and 2011 when we had a lot of snow. Since then, though, we have barely had any snow here. And the last few winters the night time temperature has hovered around zero, but not much below.
We are about to move to the Scottish Borders. about 30 miles south, 100 metres higher in altitude and a couple of degrees cooler in winter. The apple blossom there has only just come out, but up in Haddington it has been out for four weeks. So, just a small change in temperature appears to make a massive difference.
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Jack Harrison
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Re: Earlier butterfly seasons
My original post probably wasn’t clear.
It is accepted that temperature is certainly a major factor in determining emergence times.
I hoped for a discussion about what the possible effects of cleaner air / brighter sunshine in the early part of the year might have on emergence dates: in other words, how much is cleaner air an important factor?
This year (and as a parallel Switzerland in winter) brightness of the sun might be a more important factor than temperature.
Jack
It is accepted that temperature is certainly a major factor in determining emergence times.
I hoped for a discussion about what the possible effects of cleaner air / brighter sunshine in the early part of the year might have on emergence dates: in other words, how much is cleaner air an important factor?
This year (and as a parallel Switzerland in winter) brightness of the sun might be a more important factor than temperature.
Jack
Re: Earlier butterfly seasons
I'm sure brighter sunshine would probably increase radiant heat, but on the other side, pollutants in the atmosphere contribute to a greenhouse effect, trapping heat and making temperatures rise, which again might lead to earlier emergences.