For some years now I have been grappling with the possibility that global warming just could, just might, ramp up in some kind of mad accelerative way, and fry us just as we were about to drown because of sea-level rise of an unmentionable height. OK, it’s unlikely, but some people think it just might happen, and that is why we have precautionary principles, carbon taxes and RETs. Somebody believes this kind of stuff, and though I’m not one, I’m agnostic enough to be prepared to accept it if the evidence were to hove in view.
Somewhere along the way I came across a paper which seemed to suggest that the temperature of the oceans had an upper limit. I think it was around 37 degrees Celsius. The Red Sea has a maximum temperature of 36 degrees. I cannot now remember why there was thought to be an upper limit, but plainly, the hotter the water gets, the more of it will evaporate, the more evaporation, the more rain, the more rain, the cooler it gets. No matter. I’ve searched and searched and cannot find this reference. Maybe a reader will oblige.
But Judith Curry ran a most interesting article in her Climate etc website about the question of limits to extreme weather, and the original set of slides by Greg Holland, an Australian who works at NCAR, is well worth downloading. A quick summary is that as temperature rises what might happen is not that the extremes get more extreme, but that there are more warm days, no more intense hurricanes but more smaller ones, and so on. You can get a feeling for the change by looking at the following two graphs.
What you see here on the left-hand side are the graphs of hot days per month over time, beginning with October, then November, then December and then January. As time goes on, what happens at this Central Australia weather station (Giles) is that the number of hot days increases, and that the temperature of the hottest days increases too. But the maximum temperature does not. It sits at 46 degrees Celsius.
Now the same trend can be seen in Melbourne, a long way from Giles, but subject also to extremely hot days. The maximum in Melbourne, too, over these years, has been 46 degrees Celsius. Climate change (I don’t know from the Power Point slides how he defined it) has no greater effect. Indeed Holland suggests that all the effects of ‘climate change’ may have already occurred. From that I deduce that he thinks that the increases in temperature are largely aspects of ‘natural variability’, whatever that is.
I add the rider because soon or later someone has to come up with a theory about what the components of natural variability are. It is easy enough to pick holes in the orthodox AGW arguments, but my own intellectual curiosity requires appeasement too. What mixture of factors produces these ‘natural’ changes? OK, they seem not to be caused by human activity, but exactly what does cause them?
There seem to be limits to what can happen in the world of atmosphere and oceans, and while that is reassuring. I would like to know why these limits are what they are. Judith Curry attended the seminar at which Holland’s paper was given, and says that he had a sophisticated explanation. It would be good one day to be able to grapple with it.
In the meantime, my current position is that we are not in fact seeing more extreme weather. Holland doesn’t think there are more tornadoes, either, and while North America has had a long cold autumn and is experiencing snow and extreme cold in June, that too is just weather, and not ‘extreme’. It has happened before, just as we have had mild winters before.