What will climate change really mean for Ireland?
Published 21/11/2015 | 02:30
Weather and climate have been observed in a systematic way in Ireland for over 150 years, and we know a great deal about past weather and climate patterns.
But when it comes to the future, we must rely on computer models, which provide a range of projections of the future state of the climate. The range is needed to take into account the uncertainty in the future level of greenhouse gases emitted, and also uncertainties in the models themselves.
These projections indicate that the rise in global temperature is likely to exceed 2C by the end of this century - and that could rise to as much as 4.5C depending on the level of greenhouse gas emissions. This global temperature increase has so far not been uniform, for example temperatures in the Arctic have been rising much faster than the global average.
Sea levels will rise, and rainfall patterns will change, with significant regional and local variations expected. In Ireland, the average air temperature has risen by approximately 0.8C in the last 100 years, with much of the warming occurring towards the end of the 20th century. All seasons are warmer.
Some of the effects can already be seen; the start of the growing season for certain species is now up to 10 days earlier, there has been a decrease in the number of days with frost, and an increase in the number of warm days where temperatures are over 20C.
All seasons are projected to be significantly warmer (1 to 1.5C) by mid-century, which will lead to a further increase in the length of the growing season with a knock-on effect on natural ecosystems which have evolved gradually to suit our climatic conditions.
The rate at which these changes are expected to take place may not allow ecosystems time to adapt. For example, migrating birds arrive in spring and take advantage of insects emerging after winter. If the insects hatch earlier, fewer chicks will survive.
Fragile habitats in vulnerable upland, peatland and coastal areas will also come under increasing stress.
Milder winters will lead to a reduction in winter mortality due to fewer cold spells, but the increasing likelihood of heatwaves and hot days - days over 30C - may have the opposite effect in summer.
Over the last 30 years or so, rainfall amounts have increased by approximately 5pc, and there is some evidence of an increase in the number of days with heavy rain in the west and northwest.
Climate projections for rainfall have greater uncertainty than for temperature, but they indicate that, overall, rainfall amounts in Ireland might decrease slightly.
Summers are likely to become drier, while winters may be wetter, especially in the west and north. There are also indications of an increase in the number of very wet days, or days with rainfall above 20mm.
These projections, applied to river flows, show an increased risk of winter flooding, an increased risk of short duration 'flash' floods, and possible water shortages in summer due to higher temperatures and lower rainfall.
The rise in sea levels will make low-lying coastal areas more prone to flooding, especially from storm surges.
Changes in our climate regime will continue to be incrementally small and barely noticeable on a year-to-year basis, and will occur against the background of natural climate variability such as El Nino and variations in the sea temperature of the north Atlantic.
It is also possible that declining Arctic sea ice might affect regional weather patterns.
This means that we are still likely to have periods of colder weather which appear to go against the trend.
Extreme weather events will continue to occur, and while it might not be possible to explicitly attribute these to human-induced climate change, the probability of occurrence of extreme events is expected to increase.
The effects of climate change on Ireland may be less severe than those expected in other parts of the world, nevertheless we need to put adaptation and mitigation strategies in place now to ensure the best societal outcome for Ireland.
Seamus Walsh is Head of Climatology and Observations at Met Éireann