BTFP: Wet summer

This repost is part of our Summer Slowdown revisiting of the archives. This post was originally published 13th December 2007, at the time of the last La Niña event affecting Australia.

How odd it is for me to write those words after the last few dry years. The word(s) of the last weeks has been “La Niña”, the sister phenomenon to the prolonged El Nino event that has brought us severe drought year after long bloody year. Where El Nino brings eastern Australia dry weather, La Niña brings us rain. (It works the opposite way around for the farmers of the American Midwest grain-belt.)

That’s why it’s rained and rained this month, and why we got huge thunderstorms last week.

Sydney storm

I remembered La Niña was to do with the Southern Oscillation Index, as I’m sure many of you do too, but I couldn’t remember exactly what the oscillation entailed. So I looked it up, and for those wanting the Cook’s Tour, it’s all about the sea surface temperature (SST) across the equatorial Eastern Central Pacific Ocean, and how the warmer or cooler water flows via the ocean currents to modify the normal climate. An El Nino/La Niña occurs when the SST deviates from normal by more than 0.5C – if the temperature goes up we get an El Nino, and if it goes down we get a La Niña.

That the deviation occurs in the equatorial region is the reason that it affects both hemispheres, and that the effect is so significant is due to the size of the Pacific Ocean, which covers a significantly larger area than the total landmass of the planet (as Wikipedia puts it, with room for another Africa to spare). That the effect on the two hemispheres either side of the equator is so different is down to the distribution of landmass, as this New Zealand site phrases it:

Note that the south pole can be seen as a continent surrounded by oceans, whereas the north pole as[sic] an ocean surrounded by continents. Because of this, these two sides of the planet are, like cheese and chalk, totally different from one another, in oceanography, climate and environment.

Some geographers ignore the equator and divide the planet into a land hemisphere and a water hemisphere:

water hemisphereland hemisphere

.. which does tend to make one think a little differently about how the weather systems work over large areas.

There’s still a lot we don’t know about the long term effects of ocean warming on how these systems will work in the future. Will Northern Europe undergo a paradoxical cooling as the oceans warm, due to the weakening or loss entirely of the thermohaline circulation of the North Atlantic Drift? Will the Southern Hemisphere’s predicted lesser response to such changes be an asset for us if the Northern Hemisphere suffers vast climate change while our climate only changes a little, or will we end up overwhelmed by climate refugees?

That’s why conferences such as this week’s one2007’s in Bali are important, or at least important in principle (whether much that could be discussed and planned does actually get discussed and planned is a different matter). Large changes are coming as the climate changes, and we need to be prepared for the inevitable refugees and rationing. Not in a panicky, put up the fences and more stringent border patrol way, but in a measured way. I don’t think it’s actually sunk in deep enough into the psyche of our world leaders yet though. It needs more than lip service.



Categories: environment, Science

Tags: , ,

5 replies

  1. A nice summary in comments at LP of the current state of global weather variations versus actual climate change as amateurs point meaningfully at heavy snowfalls in the UK and USA:

    As for where the warm weather’s gone, the answer is Greenland and much of Arctic Canada, which has been considerably further above normal than northern Europe has been below (the UK will come in around 4-5 degrees below normal for December; significant parts of Greenland and Canada are 10 degrees or more above). It doesn’t exactly have the impact of a few centimetres of snow at Heathrow (or a lot of centimetres of snow in New York), but two of the main northern Canadian observing sites, Baker Lake and Rankin Inlet, recently reached 0 for the first time ever in December. A Greenland site reached +17 in the last week of November.
    Global temperatures for 2010 are likely to either just break or just miss a record – unlikely to be more than 0.02 degree in it either way. Out of 23 global regions only one, northern Australia, was running below normal for the year as of the end of October (northern Europe will probably join it once the December numbers are in). Seven of the 23 regions were running highest on record; four out of the five in Africa, plus south and central Asia and Greenland/Arctic Canada.

  2. P.S. And there’s a “heatwave” in Moscow – temperatures 20 degrees above normal have meant that instead of dealing with their usual heavy but dry powder snow, they have instead been dealing with sleety rain and everything iced over, which they are not used to at all.

  3. Actually we are getting all your warm weather. Most of this week has been just below 40DegC AND humid. Stifling is one way to put it.

  4. Now Julie, warm weather in other parts of the world doesn’t count to the deniers when it’s cold in Important Places! Any seasonal variation at all still happening obviously means that Global Warming is a Big Fat Lie!
    Or something like that. It’s hard to follow what passes for ‘reasoning’ with that crowd.

  5. Yes. And of course, Western Australia Does Not Count (at least as far as the Government is concerned), when talking about global warming. Because being in drought for more than a decade is somehow less important, than the much shorter drought over east *sighs*
    If only we could get some of that rain over here.

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