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.

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:

.. 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: australia, climate change, social change