THE exact date of the beginning of spring is a moot point to which no definitive answer can be found.
Meteorologists, astronomers and gardeners all agree to differ on the question - each group has its own criteria - and all with very good reason in the context of their sphere of interest.
In parts of Ireland and Britain, the popular view is that spring begins on February 1st, St Brigid's Day. To many, however, this date is spuriously early: to T.S. Eliot, for example, it was "the dark time of the year, between melting and freezing", when thoughts of any seasonal renaissance were distinctly premature.
Midwinter springs in its own season
Sempiternal though sodden towards sundown,
Suspended in time, between pole and tropic.
One way of deciding when the spring has come is to watch for the budding of the local plant life, and this can be observed on an almost global basis using satellites.
A "green wave" moves northwards in the early months of the year at an average rate of about 100 miles a week. Interestingly, it has been discovered that since satellite observations began some 30 years ago, the onset of spring in the northern hemisphere has been getting earlier each year, occurring on average about 10 days sooner now than it did in the middle of the 1960s.
But an electrical engineer, of all people, has improved on this discovery. Dr David
Thompson, of Bell Laboratories in the US, is like many of his colleagues an expert at extracting a meaningful "signal" from a somewhat chaotic jumble of electrical transmissions.
Recently he applied these techniques to long term temperature records stretching from 300 years ago until the present day. Once the "noise" of the daily ups and downs hag been removed, the rhythmic undulation of the seasonal temperature could be identified, and the position of the peaks and troughs located with unprecedented accuracy.
For most of the sequence, Thompson found that in the northern hemisphere the seasons had been occurring later and later each year, the cumulative delay amounting to a little more than a day per century.
This, it seems, is to be expected because of the idiosyncrasies of the Earth's orbit around the Sun. But after 1940 there was a dramatic shift: the seasons suddenly started to arrive earlier, rather than later, and at an accelerating rate, as also detected by the satellites.
And the exciting thing for climatologists about this long term pattern is that it is entirely consistent with their greenhouse theories about global warming.