Sunday, 1 June 2008

When will someone learn we're living in a new climate?

Recent forecasts by senior climatologists in Australia seem to suggest that after a long run of warm, dry winter southeastern Australia is set for a more historically normal winter. Some other articles have even suggested a decently cool and rainy winter is likely.

The problem is, as Tim Flannery points out in his essential The Weather Makers, the atmospheric circulation, owing to the increased levels of carbon dioxide in the atmosphere, is in a completely different state from most of the instrumental records. In the long term unless the level of carbon dioxide is completely stabilised through phasing out fossil fuels we will move to new metastable states via “magic gates” very frequently. What is a definite trend is that the winter rain belt is moving poleward with each new “magic gate”, and these “magic gates” appear to be occurring more often than at the lower carbon dioxide levels of the 1980s. By 2020 there can be little doubt that the southern winter rain areas that historically form Australia’s major cropping region will be firmly within the arid belt. Melbourne, Adelaide and even Perth will be as arid as, say, Coober Pedy has historically been.

Whenever El NiƱo should return, near-rainless winters over wheat areas of Victoria and South Australia will result. Already realistic people are saying there are no prospects for useful planting rain in southeastern Australia.

What will they be saying if there has been no significant rain in the wheat areas by July or August?

The sensible response to the new climate from both sociological and ecological perspectives of complete revegetation of southern wheat lands with native flora is viewed too costly and politically risky. However, there is nothing we can do on present or even immensely lowered carbon dioxide emissions to prevent further reductions in rainfall over southern Australia.

This means there is no use trying to base our agricultural planning for on historical climates. Instead, we should plan for southern winter rainfall much lower than the record dry year of 2006, as this is what will be expected with the cold fronts even further south than for the past three winters.

For example, we should plan for average May to August rainfall of 50 millimetres in southern wheat areas and about 100 millimetres in more humid zones like the Adelaide Hills and Melbourne and Perth catchment areas. These rainfalls would fail to provide minimal wheat crops or urban water supplies, and Flannery’s work and recent climate events both clearly demonstrate farmers and water managers should not be given short-term advice for one season, but much longer-term advice to produce the adjustment needed to cope with Australia’s twenty-first century climate map. For all the talk of a highly variable climate, the difference between Melbourne’s mean rainfall between 1858 and 1996 and that since 1997 is more than two standard deviations.

The full contours of this map have not yet drawn themselves, but will undoubtedly involve replacement of the southern winter rain belt by an arid belt extending to the Victorian coast and probably Cape Leeuwin. Should farmers and water supply managers know this, they would certainly become much longer-term in their planning and realise patterns of primary production must change completely. Most especially, neither irrigated nor rainfed cropping can exist in a climate with perenially dry streams and a growing season rainfall of 50mm, and intensive pastoral farming will suffer the same fate, leaving a pastoral economy on properties much larger than exist today as the only possibility.

1 comment:

Anonymous said...

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