The Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2001) is the most authoritative assessment of global climate change to date. Produced by several hundred leading scientists in various areas of climate studies, its principal conclusions include the following: • Global average temperature has increased by 0.6 ± 0.2°C since 1860 with accelerated warming apparent in the latter decades of the 20th century. A further increase of 1.5–6.0°C from 1990 to 2100 is projected, 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 the 1990s being the warmest decade and 1998 the warmest year. Warming has been more pronounced at 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 polar regions. Sea-ice thickness in the Arctic has declined by about 40% during late summer/early autumn, though no comparable reduction has taken place in winter. In the Antarctic, no similar trends have been observed. One of the most serious impacts on global sea 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 past century, 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 the period 1990–2100. • Precipitation has increased over the land masses of the temperate regions by 0.5–1.0% per decade. Frequencies of more intense rainfall events appear to be increasing also in the Northern Hemisphere. In contrast, decreases in rainfall over the tropics have been observed, though this trend has weakened in recent years. More frequent warm-phase El Niño events are occurring in the Pacific Basin. Precipitation increases are projected, particularly for winter, for middle and high latitudes in the Northern Hemisphere and for Antarctica. • No significant trends in the tropical cyclone climatology 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 the magnitude 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-term planning strategies will be necessary to mitigate adverse impacts. Long lead times for adjustment characterise many sectors, e.g. forestry, and it is important to provide as much advance warning of likely changes as possible to enable adaptation to commence early. By anticipating change it may be possible to minimise adverse impacts and to maximise positive aspects of global climate change.