Climate change refers to long-term changes in the earth’s weather patterns or average temperature. Interactions between the atmosphere, oceans, ice sheets, land masses and vegetation create the climate system. Changes in climate can arise naturally from long-term cycles in the earth’s orbit. El Niño/La Niña events, in which interactions between the oceans and the atmosphere cause temperature changes lasting a number of years is another example of natural variability. Since the mid-nineteenth century a rise has occurred in the average global temperature; the rate of change in recent times cannot be explained by natural causes alone. This has be shown by running sophisticated computer models of the earth’s climate system, known as earth system models, which only reproduce observed rises in temperature when the effects due greenhouse gases and aerosols are included .
There is overwhelming evidence indicating that the majority of the warming over the last one hundred or so years is due to increased amounts of greenhouse gasses in the atmosphere as a result of human activity . For a balanced climate, the incoming energy to the earth provided by the sun (solar radiation) should be balanced by energy lost by the earth; most of the energy emitted by the earth is in the form of infrared radiation. Greenhouse gases are constituent gases of the atmosphere which absorb the earth’s outgoing infrared radiation and re-emit it in all directions, including back to the earth’s surface. The most important greenhouse gases are carbon dioxide (CO2,), water vapour (H2O), methane (CH4), and ozone (O3). As concentrations of these gases rise, more outgoing radiation is absorbed, reducing the heat lost to space from the earth’s surface. The net result is that the earth absorbs more energy (from solar radiation) than it radiates and this imbalance warms the planet; this process is similar to what happens in a greenhouse.
Climate change will mean altered weather patterns across the globe, with different parts of the planet affected in different ways. There will be changes in rainfall patterns, increased desertification, melting of glaciers and ice caps, sea level rise and an increased likelihood of severe weather events. There are implication for health, food security, population displacement and biodiversity .
Climate or Earth system models are used to improve our understanding of the climate on time scales ranging from seasonal to centennial scales. They consist of mathematical equations used to mimic interactions within the Earth’s climate system including those between the atmosphere, oceans, land surface and sea-ice. Such models therefore consist of millions of lines of computer code and needs to be run on state-of-the-art supercomputers.
Climate models are not perfect; there are many sources that contribute to the uncertainty of climate projections including natural variability in the climate system, the formulation of the model itself and future emissions of greenhouse gases and other pollutants. To account for these uncertainties, we run suites of climate simulations (called ensembles) using different models and different future atmospheric scenarios.
The Intergovernmental Panel on Climate Change (IPCC) is a United Nations body, established in 1988, which evaluates climate change science. The IPCC assesses peer reviewed research on climate change and publishes assessment reports every 5–7 years.
The first IPCC assessment reports (AR1 to AR4) handled changes in atmospheric composition using Special Report on Emissions Scenarios (SRES, e.g. A2 scenario) that were based on projected emissions, changes in land-use and other relevant factors. For AR5 the new Representative Concentration Pathways (RCP) scenarios were used. These are focused on radiative forcing – the change in the balance between incoming and outgoing radiation via the atmosphere caused primarily by changes in atmospheric composition – rather than being linked to any specific combination of socioeconomic and technological development scenarios. Unlike SRES, they explicitly include scenarios allowing for climate mitigation. There are 4 such scenarios: RCP2.6 (low), RCP4.5 (medium-low), RCP6.0 (medium-high) and RCP8.5 (high), these are named with reference to a range of radiative forcing values for the year 2100 or after i.e. 2.6, 4.5, 6.0, and 8.5 W/m2, respectively
The fifth assessment report (AR5) was published during 2013 and 2014. Some of the main findings were :
- Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia
- Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years
- Human influence on the climate system is clear. It is extremely likely (95-100% probability) that human influence was the dominant cause of global warming between 1951-2010
- Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.
- Global surface temperature change for the end of the 21st century is projected to be likely to exceed 1.5 °C relative to the period 1850 to 1900 in all but the lowest scenario considered, and likely to exceed 2°C for the two high scenarios considered.
Ireland has engaged in global modelling by contributing to the scientific development of the EC-Earth global climate model, performing centennial-scale simulations with the model using supercomputers and contributing the data for assessment by the IPCC. The global modelling work was carried out by Met Éireann and the Irish Centre for High-End Computing (ICHEC) as partners in the international EC-Earth consortium.
The EC-Earth and other global models are then downscaled to provide information at a regional level for Ireland. Downscaling is a process by which global models, which have a typical resolution of 50km or more, are dynamically or statistically modelled onto a finer scale with a resolution as low as 4km, which allows a better resolution of coastlines and topography.
The impacts of climate change for Ireland were assessed for the mid-century period 2041-2060 using an ensemble of down-scaled climate simulations, based on medium-to-low (RCP 4.5) and high emission scenarios (RCP 8.5).
Projections indicate an increase of 1–1.6°C in mean annual temperatures, with the largest increases seen in the east of the country. Warming is enhanced for the extremes (i.e. hot or cold days), with highest daytime temperatures projected to rise by 0.7–2.6°C in summer and lowest night-time temperatures to rise by 1.1–3°C in winter. Averaged over the whole country, the number of frost days (days when the minimum temperature is less than 0°C) is projected to decrease by 50% for the medium-low emission scenario and 62% for the high-emission scenario. The projections indicate an average increase in the length of the growing season by mid-century of 35 and 40 days per year for the medium-low emission and high-emission scenarios, respectively .
Milder winters will, on average, reduce the cold related mortality rates among the elderly and frail but this may be offset by increases due to heat stress in the warmer summers .
The down-scaled simulations show significant projected decreases in mean annual, spring and summer precipitation amounts 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 frequencies of heavy precipitation events show notable increases of approximately 20% during the winter and autumn months. The number of extended dry periods is projected to increase substantially by mid-century during autumn and summer. The projected increases in dry periods are largest for summer, with values ranging from 12% to 40% for both emission scenarios.
Globally sea levels have been rising at an average rate of approximately 3 mm per year between 1980 and 2010. Sea level is projected to continue to rise at this rate or greater. All major cities in Ireland are in coastal locations subject to tides, any significant rise in sea levels will have major economic, social and environmental impacts. Rising sea levels around Ireland would result in increased coastal erosion, flooding and damage to property and infrastructure.
Studies have shown significant projected decreases in the energy content of the wind for the spring, summer and autumn seasons, with the projected decreases largest for summer and no significant trend in winter. The overall number of North Atlantic cyclones is projected to decrease by approximately 10 %. Results also indicate that the paths of extreme storms will extend further south, bringing an increase in extreme storm activity over Ireland, although the number of individual storms is projected to be quite small . As extreme storm events are rare, the storm-tracking research needs to be extended. Future work will focus on analysing a larger ensemble, thus allowing a robust statistical analysis of extreme storm track projections.
Changes in the climate will bring changes in the behaviour of species. A spring warming in recent years has seen and advance in the timing of key phenological phases of a wide range of organisms, including trees, birds and insects. For example, higher temperatures in late winter or early spring results in butterflies appearing earlier in the year and birds shifting their migration patterns. The pace of future change will cause stress to ecosystems which are unable to adapt quickly.
Ireland needs to put in place and implement policies to ensure that the country meets the challenges of expected changes in our climate and our international obligations. Mitigation is the term given to efforts to reduce emissions of greenhouse gases. Ireland’s current National Mitigation Plan(NMP) can be accessed here. Adaptation refers to actions taken to reduce vulnerability and exposure to expected climate change and variability. Ireland’s current National Adaptation Framework(NAF) can be accessed here.
Further Reading, Links and References
- Intergovernmental Panel on Climate Change (IPCC) 2013: available at https://www.ipcc.ch/
- Nolan, P. 2015. EPA Report: Ensemble of Regional Climate Model Projections for Ireland. EPA climate change research report no. 159. EPA: Wexford.
- O’Sullivan, J., Sweeney, C., Nolan, P. and Gleeson, E., 2015. A high-resolution, multi-model analysis of Irish temperatures for the mid-21st century. International Journal of Climatology. doi: 10.1002/joc.4419.
- Gleeson, E., McGrath, R. & M, Treanor, eds. 2013. Ireland’s climate: the road ahead. Dublin, Ireland: Met Éireann [Online].
- Nolan, P., O’Sullivan, J., & McGrath, R. (2017). Impacts of climate change on mid‐twenty‐first‐century rainfall in Ireland: a high‐resolution regional climate model ensemble approach. International Journal of Climatology.
- Dwyer N. 2012. The Status of Ireland’s Climate, 2012. Dwyer N (ed). CCRP Report No. 26. EPA, Wexford, Ireland.
- United Nations Framework Convention on Climate Change (UNFCCC) available at http://newsroom.unfccc.int/.
- Global Climate Observing System (GCOS) available at http://www.wmo.int/pages/prog/gcos/index.php.
- Caffarra, A., F. Zottele, E. Gleeson, and A. Donnelly. “Spatial Heterogeneity in the Timing of Birch Budburst in Response to Future Climate Warming in Ireland.” International Journal of Biometeorology 58, no. 4 (September 15, 2014): 509–19. doi: 10.1007/s00484-013-0720-5.
- McCarthy, G., E. Gleeson, and S. Walsh. “The Influence of Ocean Variations on the Climate of Ireland.” Weather 70, no. 8 (2015): 242–245. doi: 10.1002/wea.2543.