The present climate

The country enjoys a relatively mild temperate oceanic climate, influenced by the relatively warm waters of the Gulf Stream and the prevailing south-westerly winds from the Atlantic. The coldest months are January and February, with mean daily air temperatures of between 4⁰C and7 ⁰C while the warmest are July and August, with mean temperatures of between 14⁰C and 16⁰C (1).

Rainfall is well distributed throughout the year. In low-lying areas average annual rainfall is mostly between 800 and 1200 mm but ranges from less than 750 mm in some eastern areas to 1500 mm in parts of the west. In mountainous areas annual rainfall may exceed 2000 mm (1).

Air temperature changes until now

Mean annual temperature records closely resemble global trends, with warming evident in 2 periods, 1910 to the mid-1940s, and 1980 to 2004. The warming in the latter period occurred at a much greater rate than the global temperature increase. Nearly all stations reveal increases in annual and seasonal mean maximum and minimum temperatures (2,5).

Temperatures increased by 0.7⁰C since 1890, i.e. an average of 0.06⁰C per decade. The increase was 0.4⁰C during the period 1980-2008, i.e. equivalent to 0.14⁰C per decade. All seasons are warmer but more so in winter (2,4). Significant decreases in frost frequency and increases in ‘hot’ day frequencies are also occurring (4). In Ireland, 6 of the 10 warmest years have occurred since 1995, the warmest year in that period being 1997 (5).

The increase in temperature is not even throughout the year; a greater seasonal differentiation becomes apparent with greater increases in temperature in the summer months. The central eastern part of the country shows the greatest increase in summer temperature. The effect of climate change is to make all of the country warmer at all times of the year with less warming in the north-east and the south-west in winter (3).

Precipitation changes until now

An analysis of precipitation series for 30 stations across Ireland with an average series length of 118 years, and some stations dating back to 1870s, shows that precipitation intensity has increased in especially the east and southeast of the island. Across Ireland, the contribution of heavy and extreme precipitation events to annual totals is increasing. The results show no persistent trends in annual totals or consecutive wet or dry days, however (18). 

Changes to precipitation patterns in the previous century are more spatially and seasonally variable than temperature changes. The number of days where daily precipitation is greater than or equal to 10 mm (extreme precipitation events) reveals significant annual increases on the west coast. There has been a significant increase in total rainfall in the north and west; many stations also show increases in March and October (2).

Substantial increases in winter precipitation have occurred during the 20th century in north-western parts (over 10%) and decreased summer rainfall is apparent in the south-east (4). A rainfall dataset over the period 1850–2010 indicates positive trends in winter and negative trends in summer precipitation (11).

Data over the period 1941-2010 covering the entire country show that the precipitation amount generally increases in Ireland, particularly in the northwestern region. The most significant increasing trends for the whole study period (1941–2010) are found for late winter and spring precipitation, as well as for the annual totals. In the period from the early 1970s the increase of precipitation is general in all seasons of the year except in winter, but the statistical significance of this increase is weak (17).  

Air temperature changes in the 21st century

It is projected that by 2050 there will an increase in January temperatures of 1.5°C. Winter conditions in Northern Ireland and the north midlands will be similar to those currently experienced along the south coast. July temperatures are projected to increase by approximately 2.5°C, and there will be marked reductions in summer rainfall by 25–40% (5).

It is projected that by 2100 average warming in Ireland will be 1–3⁰C, compared to the 1961–2000 average (2).

Future cold spells in Western Europe are projected to become about 5°C warmer (and remain above freezing point), thus having a significant climatic impact. This conclusion is based on research in which a cold spell (CS) is defined as a non-interrupted sequence of days in which the 5-day average temperature falls below a threshold value Tcold (8).

Northern Ireland

Projections of future change (measured relative to the 1960-1991 baseline) for Northern Ireland if high emissions continue are an increase in mean winter temperature very likely to be between 0.3-1.7ºC by 2020s, 1-2.9ºC by 2050s and 1.7-4.4ºC by 2080s, and an increase in mean summer temperature very likely to be between 0.3-2.1ºC by 2020s, 1.1-4ºC by 2050s and 4.2-6.2ºC (7).

Output from three GCMs and two IPCC emissions scenarios (A2 and B2) have been used to downscale daily maximum and minimum temperatures to nine climatological stations across Northern Ireland (9). Results illustrate a progressive warming for both maximum and minimum temperatures. The results, averaged across all GCMs, emissions scenarios, sites, and seasons, are:

Period Maximum temp. Range Minimum temp. Range 2011-2040 0.8 0.0-1.6 0.8 0.0-1.8 2041-2070 1.4 0.5-2.3 1.4 0.5-2.6 2070-2099 2.2 0.9-3.8 2.1 0.8-4.2

These results lie within the temperature range of previous studies (10). Autumn is the season projected to experience the most warming, for both maximum and minimum temperatures, with spring projected to increase the least. The number of frost days is projected to decline considerably for all sites, with an average of 219 less frost days over the 30-year period centred on the 2080s from the modelled baseline period 1961–1990 (9).

Precipitation changes in the 21st century

The impacts of climate change on precipitation over Ireland have been assessed for the mid-century period 2041-2060 (compared with the reference period 1981-2000) using an ensemble of downscaled climate simulations (three high-resolution RCMs, driven by four global climate models), based on medium-to-low and high emission scenarios (SRES B1, A1B and A2 scenarios and RCP4.5 and RCP8.5). The results of this assessment show the following (15):

• Mean precipitation: Significant projected decreases in mean annual, spring and summer precipitation amounts are shown by mid-century. The projected decreases are largest for summer, with reductions ranging from 0 to 13% and from 3 to 20% for the medium-to-low and high emission scenarios, respectively. The drying signal for autumn is less robust. A projected increase in mean precipitation for winter was noted over most of Ireland for the high emission ensemble, but this should be viewed with a low level of confidence.
• Heavy precipitation: The frequencies of heavy precipitation events (daily precipitation greater than 30 mm) show notable increases of approximately 20% during the winter and autumn months, probably due to an increase of the number of intense storms (16).
• Dry periods: In this study a dry period is defined as at least five consecutive days for which the daily precipitation is less than 1 mm. The number of dry periods is projected to increase substantially by mid-century during autumn and summer. The projected increases in number of dry periods are largest for summer, with values ranging from 12 to 40% for both emission scenarios. The autumn projected increases in number of dry periods range from 3 to 39% for the medium-to-low emission scenarios, and from 1 to 32% for the high emission scenarios. The annual projected increases in number of dry periods range from 7 to 28% for the medium-to-low emission scenarios, and from 2 to 25% for the high emission scenarios.

For the 21st century decreases are projected of approximately 25% in amounts of summer receipts. Geographically, these are most significant in the south-east where decreases of summer rainfall amounts in excess of 40% are anticipated over the next five decades (2,4). Wetter winters are projected in the west in 2021-2060 compared to 1961-2000 (2).

Northern Ireland

Projections of future change (measured relative to the 1960-1991 baseline) for Northern Ireland if high emissions continue are a change in winter mean precipitation very likely to be between -3 to +10% by 2020s, 2 to 19% by 2050s and +6 to +34% by 2080s, and a change in summer mean precipitation very likely to be between -15 to +10% by 2020s, -28 to +4% by 2050s and -39 to +4% by 2080s (7).

Wind climate changes in the 21st century

It is highly uncertain how winter storm tracks over the North Atlantic Ocean may change under climate change this century (13). Following the general consensus in the literature to date, the average wind changes over the North Atlantic by the end of the century are small and negative and less than the high natural interannual variability of the region (14). Natural variability is large and dominant and is projected to remain so for the century to come. A recent study shows that mean wind speed at 10 m height will decrease this century up to 3% over the North Atlantic Ocean for all seasons under moderate (RCP4.5) and high-end (RCP8.5) scenarios of climate change. This study was based on global climate model projections for the period 2070 - 2099 compared with 1980 - 2009. The study also shows that wind extremes and storminess over the North Atlantic Ocean will also decrease: the 5% strongest winds (the so-called 95th percentile of all wind speeds) will decrease by up to 15%. Wind climate changes over the North Atlantic Ocean not necessarily reflect future changes in wind climate over Ireland, however: the projected decreases in the frequency and intensity of wind storms crossing Ireland are not statistically significant (12).

Wind speeds could be about 10% stronger in winter on average by mid-century (measured at a height of 60-metres), but about 15% lighter in summer. Wind speed is another very uncertain variable, however (6).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Ireland.

1. Department of the Environment, Heritage and Local Government (2010)
2. McElwain and Sweeney (2007), in: Department of the Environment, Heritage and Local Government (2010)
3. Environmental Protection Agency (2003)
4. Sweeney et al. (2002), in: Environmental Protection Agency (2003)
5. Department of the Environment, Heritage and Local Government (2007)
6. Irish Academy of Engineering (2009)
7. UKCIP09 UL Climate Projections 09, in: Northern Ireland Environment Agency (2009?)
8. De Vries et al. (2012)
9. Mullan et al. (2012)
10. Arkell et al. (2007); Fealy and Sweeney (2008), both in: Mullan et al. (2012)
11. Noone et al. (2016)
12. Gallagher et al. (2016)
13. Church et al. (2013), in: Gallagher et al. (2016)
14. Collins et al. (2013), in: Gallagher et al. (2016)
15. Nolan et al. (2017)
16. Nolan (2015), in: Nolan et al. (2017)
17. Domonkos et al. (2020)
18. Ryan et al. (2022)