Monday 17 December 2018

We cope better with extreme weather now - but for how long?

Ireland has suffered severe weather events for a thousand years, but we cannot definitively blame climate change, writes climate expert John Sweeney

Enjoying the snow in the Phoenix Park, Dublin. Photo: Colin Keegan, Collins Dublin.
Enjoying the snow in the Phoenix Park, Dublin. Photo: Colin Keegan, Collins Dublin.

John Sweeney

It is not known who wrote the Annals of Innisfallen, most probably a monk in the 11th Century on the island of that name in the middle of Lough Leane, near Killarney. But whoever it was commented on a blizzard in 1028 as follows: "Great snow in the Lent of the above year for three days and three nights so that neither people nor cattle left their houses."

Almost a thousand years later, in the Lent of 2018, the exact same observation could have been made. Having come through what will probably emerge as a once-in-a-generation snow event, it is worth reflecting on where it fits with some of the more comparable events of the last century.

Comparisons are always difficult with snow events owing to differences in how societies are organised or adapted over time to better cope with them.

Snowfall and snow depth are also notoriously difficult to measure objectively. Snow doesn't fall neatly into a rain gauge. Wind, and short-term temperature changes between measurements, complicate things further and make comparisons between snow events over time less reliable than with more easily measured weather parameters. Nonetheless, the big snow events register for a long time in the public consciousness. Just as many of us can remember where we were in January 1982, so the beginning of March 2018 will be a psychological marker for a long time.

Perhaps the worst event of the past 100 years was the winter of 1947. From late January to early March, snow fell on 30 days and in places persisted on the ground right up until May. Post-war rationing of basic foodstuffs, fuel shortages and poor road infrastructure made for even more hardship, with several hundred deaths reported in Ireland. People burned their furniture to keep warm. A few brave souls held a ceilidh on frozen Lough Key in Roscommon.

Many major events bear a similarity in their meteorological set-up to the events of this week. The Beast from the East's ancestor produced the century's coldest winter in 1962-63. So cold was it that when snow did eventually arrive at the turn of the year, it was very slow to disappear. It fell to a depth of 45cm in Dublin on New Year's Eve and the freeze hardly eased until March. Villages in the east were cut off while, in the west, cold was the issue. The Shannon could be crossed on foot outside Limerick.

More vivid memories for most will be recalled from 1982 when 25cm of snow on January 8 and 9 brought the country to a standstill. The scramble for bread and milk seen in recent days occurred then as well, and powdered milk had to be reconstituted to meet demand. Motorists struggled to get their cars over the canal bridges in Dublin. The Air Corps delivered emergency supplies of milk by helicopter to some villages cut off by drifts of more than 2m and it was reported that the Canadian government took pity on Ireland and donated six snowploughs for future use.

There are some positive lessons to be learnt from the current extreme event. Firstly, the value of professional weather forecasting, which prepared the nation well for what was coming, was clearly demonstrated.

The coordination of public services was not a feature of the earlier episodes but was well demonstrated this time around. Better communications, better insulated houses, better social and healthcare, better emergency services - we have come a long way from 1963 and even from 1982. But people still die of cold. Research carried out in Maynooth University indicates that the death rate, mostly involving the elderly and other vulnerable groups, increases by around 20pc in sub-zero temperatures compared with values around 10C. Continued improvement in housing standards is essential and is a win-win situation not confined to reducing exposure to cold.

Climatically, the number of days per year with snow, and the number of days when snow is lying on the ground, is in decline as Ireland warms up. But extreme events like this week will still occur. In a study of maximum snow depths published six years ago, Met Eireann mapped the depths with a return period of 50 years. For areas below 100m in altitude, the figure of 35cm only applied to central Co Wicklow and a small part of Co Monaghan. Elsewhere, values of 20-30cm applied as a once in a half-century occurrence. It will be interesting to see what figure emerges from the current event.

Looking beyond the confines of Ireland, there is a bigger picture to address. It is whether the wanderings of the jetstream that were implicated in bringing the Siberian air to Ireland and Storm Emma from the Atlantic are indicative of other climate agents at work. Last week the North Pole warmed above freezing point and last month it snowed in parts of the Sahara desert. Are these simply rare natural events or are they at least partially attributable to the greenhouse-related rapid warming of the Arctic? As the Arctic sea ice dwindles and the newly opened ocean radiates heat, the equator-pole temperature difference that drives the jetstream reduces. The jet weakens and meanders more, producing extremes of various kinds.

While we can't tie individual events like the last week definitively to climate change forcing - further research is still needed to do so - the time to join the dots in terms of global extreme events may soon arrive.

One hopes that in another thousand years a resident of Innisfallen doesn't write that in the 21st century the Irish ignored the climatic signals for short-term economic gains and left a damning legacy for those who followed. They might by then even welcome a bit of snow!

John Sweeney is Emeritus Professor in the Irish Climate Analysis and Research UnitS (Icarus), Department of Geography, Maynooth University

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