Warmer but wetter: rising mercury and rainfall recorded in past 30 years

IRELAND’S AVERAGE temperatures have risen by 0.75 degrees over the last two decades, new Met Éireann figures indicate.

The rise has been described as “significant” and in line with projections of a 3-6 degree increase in world temperatures by the end of the century.

Met Éireann’s head of forecasting, Gerald Fleming, said the increases showed there was “no argument” that the weather was getting warmer, but he cautioned against seeing that as a trend.

He said the dispute was whether this was caused by man-made carbon dioxide emissions or simple variability in climate.

The spring and summer months are significantly warmer. The south Leinster and east Munster areas have recorded the greatest average rise in temperatures.

The Irish climate is also getting wetter. Valentia Observatory in Co Kerry recorded the equivalent of a month’s extra rainfall in the 30-year period between 1981 and 2010 compared to the equivalent period between 1961 and 1990.

The west of Ireland is on average 8 per cent wetter than it was in the previous 30-year period.

It will come as no surprise, given the wet summers of recent years, that the average increase in rainfall in July across the country is 15 per cent, a figure which Met Éireann senior climatologist Séamus Walsh described as the “most surprising” of all to emerge from the new data.

July is the warmest month, followed by August and June. The coldest month is January, followed closely by February and then December.

Autumn is warmer in Ireland than spring.

Met Éireann’s climate averages for Ireland are based on 10 million pieces of data collected over a 50-year period dating back to 1961.

The long-term average temperatures of the period 1981-2010 show a 0.5 degree increase in comparison to 1961-1990, which is the baseline for measuring climate averages.

However, when the overlapping years between 1981-1990 are discounted, the difference in temperatures between the periods 1961-1980 and 1991-2010 is 0.75 degrees.

“When you look at long-term averages, 0.5 of a degree is a lot,” Mr Fleming said.

“If you look at what is being said about a rise in temperature by the end of the century, an increase of 0.5 of a degree in a 20- to 30-year period is actually quite significant.”

Overall the country has had a 5 per cent increase in rainfall between the two 30-year periods.

While the amount of rainfall in Dublin has increased by just 2 per cent, there has been a rise of closer to 8-9 per cent in the west of Ireland, with a clear east-west split in a line stretching from Cavan to Waterford.

Mr Walsh said rainfall patterns were prone to variability.

The increases in rainfall may be the result of the wet summers of 2007, 2008 and 2009 and the flood conditions of 2009 which were a once-in-500-years event for many parts of the west of Ireland.

“There is huge year-to-year variability in rainfall,” he said.

“Where you get very wet summers in the noughties, they contributed to the increases in rainfall.

“There is no evidence that there is a change in the extreme values of rainfall. We have looked at that and there are no definite trends.”

Mr Walsh said temperature was a much more stable indicator of climate change.

He said there was a “definite trend” in a decreasing number of frosty days.

Sunshine levels have showed little variability by comparison, though the sunniest parts of the country, along the east and south coasts, have seen sunshine increases of more than 5 per cent in certain months.