Climate Change: Scenarios and Impacts for Ireland ERTDI Report 15 - Sweeney et al.

Executive Summary

The Third Assessment Report of the IntergovernmentalPanel on Climate Change (IPCC, 2001) is the mostauthoritative assessment of global climate change to date.Produced by several hundred leading scientists in various areas of climate studies, its principal conclusions includethe following:

• Global average temperature has increased by0.6 ± 0.2°C since 1860 with accelerated warmingapparent in the latter decades of the 20th century. Afurther increase of 1.5–6.0°C from 1990 to 2100 isprojected, depending on how emissions of greenhouse gases increase over the period.• The 20th century was the warmest of the last millennium in the Northern Hemisphere, with the1990s being the warmest decade and 1998 the warmest year. Warming has been more pronouncedat night than during the day.
• Reductions in the extent of snow cover of 10% have occurred in the past 40 years, with a widespread retreat also of mountain glaciers outside the polarregions. Sea-ice thickness in the Arctic has declinedby about 40% during late summer/early autumn, though no comparable reduction has taken place inwinter. In the Antarctic, no similar trends have beenobserved. One of the most serious impacts on globalsea level could result from a catastrophic failure of grounded ice in West Antarctica. This is, however,considered unlikely over the coming century.
• Global sea level has risen by 0.1–0.2 m over the pastcentury, an order of magnitude larger than the average rate over the past three millennia. A rise of approximately 0.5 m is considered likely during theperiod 1990–2100.
• Precipitation has increased over the land masses ofthe temperate regions by 0.5–1.0% per decade. Frequencies of more intense rainfall events appear tobe increasing also in the Northern Hemisphere. Incontrast, decreases in rainfall over the tropics have been observed, though this trend has weakened inrecent years. More frequent warm-phase El Niño events are occurring in the Pacific Basin. Precipitation increases are projected, particularly forwinter, for middle and high latitudes in the Northern Hemisphere and for Antarctica.
• No significant trends in the tropical cycloneclimatology have been detected.

These global trends have implications for the future course of Ireland’s climate which it is judicious to anticipate. This report presents an assessment of themagnitude and likely impacts of climate change in Ireland over the course of the current century. It approaches this by establishing scenarios for future Irish climate based on global climate model projections for the middle and last quarter of the present century. These projections are then used to assess probable impacts in key sectors such as agriculture, forestry, water resources,the coastal and marine environments and on biodiversity.

The purpose of the report is to firstly identify where vulnerability to climate change exists in Ireland and what adjustments are likely in the operation of environmental systems in response to such changes. In some sectors, e.g.agriculture, some new opportunities may arise. In other instances, e.g. water resource management, long-termplanning strategies will be necessary to mitigate adverse impacts. Long lead times for adjustment characterise many sectors, e.g. forestry, and it is important to provideas much advance warning of likely changes as possible toenable adaptation to commence early. By anticipating change it may be possible to minimise adverse impactsand to maximise positive aspects of global climate change.