This month has been warmer than average but not exceptionally so, writes Brendan McWilliams.
The statistics in recent days have confirmed what everyone has known: that this has been a very, very mild October.
The temperature in Dublin a day or two ago rose to 19.9 degrees. Much the same has been happening across the channel, where temperatures in excess of 20 degrees have occurred recently in eastern parts of England and Scotland. Wednesday last was the warmest October 27th in Britain since records began.
Twenty degrees is rare in Ireland in October but by no means a record. The highest October temperature ever experienced on this island occurred 97 years ago when the thermometer at Clongowes Wood College registered 25.2 degrees on October 3rd, 1908.
By contrast, the average highest temperature we have a right to expect on a typical October day is 13 or 14 degrees. Yet this month average temperatures have been running one to two degrees above the norm.
The immediate reasons for this are easy to discern. The air that flows at any particular time across our country is the victim of its history and its earlier environment. The airflow over Ireland during October has been almost exclusively from the southwest or south. Such air is inevitably very mild and humid.
There is nothing intrinsically odd about this weather pattern. It is a bit unusual for our October air to have originated so far south, but it has happened before.
But has it anything to do with global warming? We should remember that in Ireland this October has not been a record-breaking month. October 2001 was even milder, and with the temperature in Dublin touching 21.2 degrees it was the warmest October for over 30 years.
That takes us back to 1969, when October was exceptionally mild in circumstances that had nothing to do with global warming.
However, the current weather is consistent with the recend trend of above-average temperatures over extended periods. We cannot simplistically ascribe one warm October directly to the "greenhouse effect", but the current anomalously warm spell is consistent with what we might expect on our journey towards a "greenhouse" world.