Tuesday, July 23, 2024
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Flood and drought predictions don’t hold water


ACCORDING to the Intergovernmental Panel on Climate Change (IPCC), for each degree of global warming, the amount of water vapour in the air should increase by about 6-7 per cent. As with so many things the IPCC talks about, this small change is supposed to lead to calamity. That’s because increasing water vapour is supposed to lead to ‘intensification of the hydrological cycle’, in other words floods and droughts.

Demetris Koutsoyiannis, a hydrologist at the National Technical University of Athens, has undertaken a major review of the scientific data to see what evidence there is for this happening in practice. His findings, currently up for open peer review at the journal Hydrology and Earth System Sciences, make uncomfortable reading for the IPCC and its fellow-travellers on the bandwagon of doom.

It seems, for example, that although relative humidity is supposed to stay constant under global warming, it is actually falling. Dew points are supposed to be increasing, but mostly they are not; in particular there appears to be little or no change in equatorial regions, where the largest share of evaporation of water from the oceans takes place. If we’re not seeing change there, increased flooding is off the agenda.

And Koutsoyiannis finds that the amount of water vapour in the air is increasing at roughly one third of the IPCC’s predicted rate. If the rate of water vapour increase really is so low, then by the time we hit the (in)famous two-degree target for global warming, we’ll still only have experienced a 4 per cent increase, which as Koutsoyiannis points out is negligible given the normal variability of hydrological cycles. Where are the deluges and floods going to come from?

It doesn’t end there. There are lots of other ways in which intensification of the hydrological cycle might show up. You can measure the amount of water vapour in columns of the atmosphere. That should be increasing with global warming too, right? Koutsoyiannis finds no trend. Average rainfall across the planet should increase too – the IPCC says by 1-3 per cent per degree of global warming. The problem with this claim is that it’s within the ‘noise’ of normal variability anyway; no surprise then that Koutsoyiannis sees no meaningful trends in the data. The limited data on evaporation are telling the same story (or lack of one) too.

What about extremes of rainfall? Koutsoyannis reviews a variety of measures: changes in daily maxima, days with rainfall over a threshold and so on, he looks on land and he looks at sea. He draws a blank everywhere.

As well as being an eminent scientist, Koutosoyiannis also has a deep interest in the scientific knowledge and practice of the ancient world, and this has coloured his view of the climate scare. As he says in his conclusions, the small changes that are exciting climate scientists today would not even have been discussed by ancient engineers, who would have seen them as just noise in the ever-changing patterns of hydrological cycles. Similarly, he points out that such small changes are of no interest to those making practical decisions about flood protection and water storage. And he wonders whether, with the data refuting the climatologists’ predictions so clearly, it isn’t time that hydrologists shifted their attention away from prophecies of doom, and back on to making a real contribution to people’s lives.

You can see his point.

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Andrew Montford
Andrew Montford
Andrew Montford is the Director of Net Zero Watch. He can be found on Twitter at @adissentient.

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