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, however, the popular view is that spring begins on February 1st, St Bridget's Day, and by that reckoning, the start of spring was yesterday.
One way of deciding is to watch for the budding of the local plant life. This no doubt was the criterion used by Oliver Goldsmith, when he described his once idyllic, but by now deserted, village as a place . . .
Where smiling Spring its earliest visit paid,
And parting Summer's lingering blooms delay'd.
The equivalent place here in Germany is the Rhine valley, where spring arrives sooner than anywhere else at the same latitude, advancing northwards as a green tongue extending up the valley.
Its early arrival is caused by the Fohn effect of the high mountains on either side of the flat, broad catchment area. So far this year, however, there is no sign whatever of this surge of greenery.
When it does come, however, the advance of spring can be observed by 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.
Going even further back, it is possible to analyse long-term temperature records stretching from 300 years ago until the present day. Once the tremor of the daily ups and downs has been removed, the rhythmic undulation of the seasonal temperature can be identified, and the position of the peaks and troughs located accurately.
For most of the sequence in the northern hemisphere the seasons have 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 since 1940 there has been a dramatic shift: the seasons have started to arrive earlier, rather than later, and at an accelerating rate, as is also detected by the satellites. And this, of course, is entirely consistent with current greenhouse theories about global warming.