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Evidence points to fundamental shift in climate

25 Aug 2012

The Irish Times

PAUL GILLESPIE

TIPPING POINTS, paradigm shifts and critical junctures. These are some of the main concepts used by natural and social scientists to explain radical change. There is an interesting convergence between the different approaches, offering insights on current debates about climate change, global warming and extreme weather events.

All efforts to explain major change in big structures and large processes, by making huge comparisons, come up against the problem of how to interpret the relationship between particular events and longer-term trends.

Current discussions about the significance of the admittedly extreme drought in the United States corn belt and the persistently wet Irish summers focusing on the role of the transatlantic jet stream are a good example.

The jet stream flows between five and 10 kilometres above the E arth, determined by the border between cold Arctic and warm tropical air. Normally it moves north or south of Ireland, giving us a more varied summer, but for the last few years it has been locked in a position that gives us cool wet weather. The reverse is happening in the US.

Normality becomes an issue because climate scientists debate whether these events are more or less unusual. The US drought is the worst in 56 years and has had worldwide consequences for food supplies, while this summer has been one of the wettest in Ireland, although still within expected averages over 30 years.

But given the alarming news this week that the Arctic sea ice is about to reach its lowest recorded extent as a result of human-induced global warming, and knowing this will deeply affect climate patterns, it is perverse not to ask whether we are at a point that could trigger more radical change.

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