Nature Notes - Spring has sprung ... or has it?

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WELL, according to the Met Office spring sprung last Tuesday on March 1 – Humbug I say my spring begins in two weeks time on the March 21 as it always has!

It seems the Met Office has little time for celestial patterns and historical precedent. It picked March 1 for simplicity’s sake, choosing to slot the four seasons neatly into the 12 months ... June, July and August are the summer months; September, October and November autumn, and so on.

Historically spring starts on the day of the vernal equinox, which usually occurs on the night of March 20/21. Vernal comes originally from the Latin word for bloom and refers to the fact that, in the northern hemisphere, this equinox marks the end of winter and the beginning of spring.

An equinox is a time when the nights are as long as the days and the vernal equinox is recognised the world over as the start of the new astrological cycle. But does that necessarily make it the start of spring? After all, summer is commonly decreed to start on 21 June - the Summer Solstice - yet the following day is known as MID-summer’s day.

According to new research Spring is arriving almost two days earlier, according to new research that shows how climate change is affecting the seasons. Researchers in the US and Canada looked at seasonal temperature change around the globe over the last century.

Compared with the early part of the 20th century, the spring rise and autumn drop in temperatures are happening about 1.7 days earlier than before. The winter-summer temperature differences are also becoming less extreme.

In the UK there has already been anecdotal evidence of spring coming earlier as people notice daffodils coming up or butterflies and birds appearing early.

However, the new findings, published in Nature magazine, show how climate change is affecting the seasons on a much wider scale than previously understood. In the long term this could have an impact on wildlife around the world. Dr Alexander Stine, author of the study from the University of California, said the recent trends are very irregular and cannot be explained by natural variability.

“The annual cycle in the Earth’s surface temperature is extremely large - comparable in magnitude to the glacial–interglacial cycles over most of the planet.”

Professor David Thomson, co-author of the study, said the shift in temperatures – compared to earlier changes – suggest man-made global warming. He said: “This shift, and the changes in amplitude, are highly unusual when compared with the data from between 1900 and 1953, implicating human agency as the cause.”

Prof Thomson, of Queen’s University in Canada, said it was known that increasing the concentration of carbon dioxide in the atmosphere results in an increase in Earth’s surface temperature. The new evidence shows CO2 levels could also be affecting the timing of the seasons, which in turn would impact on the wider environment.