Friday 26 May 2017

The crystal ball is foggy at best for predicting our weather

Bridie Willers outside her flooded house at Grannagh, Ardrahan, exactly a year ago Photo: Andrew Downes
Bridie Willers outside her flooded house at Grannagh, Ardrahan, exactly a year ago Photo: Andrew Downes

Peter Thorne

Globally, 2016 will undoubtedly go down as the warmest year since modern record-keeping began in the mid-19th century.

It shall be the third such record warm year in a row; 15 of the 16 warmest years will have occurred since 2000. Briefly in early 2016, global surface temperatures flirted with or even exceeded 1.5 degrees above pre-industrial levels - a target agreed on in the Paris Climate Agreement as a warming threshold that should be avoided.

Global mean temperatures are likely to decline temporarily over the coming months as the influence of the El Nino - a natural event leading to unusually warm waters in the equatorial Pacific - continues to dissipate.

But the long-term direction of travel is upwards, and the primary cause is clearly the release of heat-trapping gases from human activities.

Regionally, the most noteworthy climate events of 2016 have been in the Arctic, which in many senses is the canary in the coal mine of climate change.

Arctic conditions have changed so much that last summer the Irish sailboat Northabout undertook a complete circumnavigation of both the Northeast and fabled Northwest Passages unaided in one season - unthinkable even a decade ago.

In the 19th century, great explorers such as John Franklin met their fates in attempting this voyage in reinforced ships stranded fast in thick multi-year ice. This year, a little Irish sailboat made it through unaided and hardly saw any ice in the Northwest passage.

Over a century ago, that passage was chock-fast with ice, and had to be transited by boat and sled by the great Irish explorer Robert McClure in 1854.

Last winter, and then again this autumn and winter, temperatures in the Arctic have regularly been more than 25C above normal.

Last winter, temperatures at the North Pole temporarily hit zero C - a 'balmy' temperature attained normally briefly in summer.

The sea-ice has been the lowest for time-of-year on record for a staggering 186 days in 2016, often by a very large margin.

Such Arctic sea-ice changes will have impacts for Ireland. Changing what once was sea-ice areas to open ocean may fundamentally alter atmospheric circulation patterns in the mid-latitudes in ways that change our weather and climate.

This is an area of active research and several recent winters are consistent with the possible effects, with some areas wet and warm and others cold and dry.

The bottom line is that, unlike gambling in Vegas, it is highly unlikely that what happens in the Arctic shall stay in the Arctic: there shall be impacts and they will be felt in Ireland over coming years and decades in ways that are, as yet, not entirely clear.

Ireland started 2016 off on the back of record rainfalls in December 2015.

Colleagues at Maynooth University led by Dr Conor Murphy have worked on producing long-term national rainfall records from instrumental, documentary and proxy sources.

Overall, the winter of 2015/2016 was almost certainly the wettest since these records began. Indeed, the 2015/2016 winter rainfall was so substantial that we could measure the effect from space.

A pair of satellites that are capable of measuring gravity anomalies showed Ireland had put on weight equivalent to a layer of water 5cm deep over the winter of 2015/2016.

The good news is that as we have slowly but surely dried out over 2016 this has diminished so we have all collectively lost weight.

Autumn was particularly dry across most of the country, although parts have yet to properly dry out.

While summer was undoubtedly a mixed bag weather-wise, there were some periods of reasonable weather, particularly away from the North West.

Temperatures in July in some locations did hit highs exceeding 30C.

Over the long-term, Irish temperatures have broadly mirrored global changes. A typical year now is about 0.5C warmer on average than in the mid-20th century, and this past year was no exception to that pattern.

What of 2017? Globally, it is almost certain to be cooler than 2016 was. Arctic sea-ice may well be a developing story if the weather in spring and early summer is conducive to melting what shall be unusually fragile ice cover.

Ireland will likely, over the year as a whole, be warmer than was typically the case 50 years ago. But climate change does not mean the end of weather - there will still be storms, cold spells, hot spells and nondescript spells. Beyond that, the crystal ball is foggy at best.

We live in a global climate that is changing and no country is truly immune to such changes. This particular story has a very long way to run yet.

How it ends depends upon our collective choices as a global society.

Professor Peter Thorne is a climatologist at NUI Maynooth

Irish Independent

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