"Every man," according to John Donne, "is a piece of the Continent, a part of the main." Some of us, however - climatologically speaking, at any rate - are more continental than others. When all other things are equal, like latitude and height, it is a matter of common experience that there is a marked difference in climate between places situated at the centre of a great land mass and those, like Ireland, contiguous to an ocean. Weather people, with disarming clarity, call this factor the continentality of a given spot.
This feature has been particularly noticeable in the last few days with reports from Moscow of temperatures in the region of -30 Celsius. But even in the middle of a cold snap of the kind we have had in recent times, the potential harshness of our Irish weather is mollified by the Atlantic Ocean on our doorstep. This great storage heater is slow to surrender the heat it has accumulated during the summer, and our winter temperatures are further moderated by the warmth of the Gulf Stream lapping on our western shores.
Moscow, by contrast, is left to scavenge what heat it can from the weak winter sun - and this is very little. A large block of land in mid-latitudes at this time of year loses much more heat during the long cold nights than it can recover during the day, and so the thermometer reading sinks inexorably downwards.
But there is another factor which affects the local temperature: the direction from which the wind is blowing at the time - or more precisely, the path followed by the air before it reaches a particular spot. If the air arrives, as it sometimes does in Ireland, from the warm and balmy regions of the equatorial Atlantic, it will be mild and humid, even in the depths of winter; but if it originates in the frozen Arctic, or blows across the icy wastes of Mongolia and Siberia, as did the breezes blowing over Moscow recently, naturally the weather will be cold and raw.
And indeed these winds blowing westwards over Moscow have come from one of the coldest regions of the world. The lowest temperatures on this planet occur in Antarctica, the record being 89 degrees recorded on July 21st, 1983, at Vostok, a Russian scientific base at the centre of the Antarctic polar ice sheet. But Vostok is only a temporary installation; the coldest permanently inhabited place in the world is reckoned to be the village of Oymyakon in Siberia, where the temperature has been known from time to time to drop below -70 degrees.