We can have confidence in Met Éireann's forecast on climate change, writes Brendan McWilliams.
The most benign hypothesis for Ireland in a greenhouse world seems in many ways a consummation devoutly to be wished. It would involve a gradual and orderly rise in Irish temperatures over the next 100 years or so, the equivalent, perhaps, of moving Ireland 400km to 500km to the south to end up miraculously somewhere near the Loire valley.
Many crops that cannot be grown in Ireland would become viable, agricultural production would soar, we would have long glorious summers like 1995 in perpetuity, and our beaches would rival those of Nice and San Tropez. "Chateau Wexford" would be a vivacious, perky little vintage.
But the truth, as Oscar Wilde remarked, is never pure and rarely simple. The above scenario might be deduced from the outputs of the current global climate models (GCMs), which have been developed to provide us with a climatic picture of the future, and which are now widely accepted as believable.
They predict that without concerted action to reduce the human influence on the world's climate, the world's average temperature is likely to increase by two degrees Celsius or thereabouts by the end of the present century, the changes being significantly more or less depending, inter alia, on the success or otherwise of measures to control greenhouse gas emissions.
But this is the big picture, a rough average for the entire world. Within this global average, assuming it turns out to be correct, we will inevitably find large regional variations and anomalies; in some places temperatures will increase significantly more than the predicted mean figure, while other places will experience less warming or may even become colder than they are at present.
The report published by Met Éireann yesterday, Climate Change - Regional Model Predictions for Ireland, tries to identify Ireland's place on this climatic spectrum.
GCMs paint the climatic picture with only very broad brush strokes. They take as their starting point a large number of "grid-points" on the Earth's surface and at various levels in the atmosphere, at each of which the current climatic conditions are concisely specified; computers then repeatedly apply mathematical formulations of the known atmospheric processes at these grid-points to arrive at a picture of the future climate.
But because of the vast number of calculations required to process data for the whole globe, the grid-points, even using the largest computers available today, cannot be any closer together in the horizontal than, say, 200km-300 km; if they are any closer, the whole ensemble is beyond the computational capability of even the very largest of computers.
Today's GCMs, in a sense, produce broadly accurate but fuzzy pictures.
The answer is an RCM, a regional climate model. This is like a magnifying glass used to bring an area into sharper focus. It concentrates on a particular region, with the conditions at the edge of the area of interest specified at any given time by the predictions of the full global models; over this much smaller area, a finer array of grid-points can be used, and the specification of a future climate can be extracted in much greater detail.
Met Éireann's RCM is an adaptation of HIRLAM, the high resolution limited area model used by the organisation for forecasting the daily weather.
Since HIRLAM, as its name implies, focuses on a relatively small area in the vicinity of Ireland, a grid-spacing of 10km-15km can be used. The output from global models is used to keep the predictions more or less on track, and consistent with accepted worldwide trends, while HIRLAM, suitably adapted to produce long-range climatic outputs, is used to work out the local Irish detail.
Climate Change - Regional Model Predictions for Ireland is the result, and can be confidently accepted as a best guess, based on current knowledge, of what the future has in store.