I asked about global warming and the conversation suddenly got all complicated and you were all worked up about something.
Um, didn’t you used to say that about ice sheets?
Worked up! You have no idea!
OK, We’ll review, cause this is the part where we start diverging from the conventional wisdom a bit.
First of all, the sensitivity is likely between 2.5 C and 3 C per CO2 doubling or equivalent. Nature might add to the carbon we release, but (knock wood) probably not immediately that much. Our distant descendants, should we manage to have any, may have to deal with it on a big scale in thousands of years.
So 2.5 C to 3.0 C?
Err, yes, we used to, and we don’t anymore. Heh. Anyway, let’s leave the methane business aside for now, we are trying to get at the core of the argument.
Probably between 2.5 C and 3 C per CO2 doubling or equivalent (or really 0.6 to 0.7 C perW/m^2 at the TOA).
err, I’ll take the first one, thanks
and almost surely between, say 1.5 and 5C .
Hang on! Hang on! I saw you said 2.5 on Kloor’s. Isn’t that false precision?
It’s spelled “2.5”, its pronounced “roun’ two ‘n’hafferso”, and it means “between 2.5 C and 3 C” . Did you want me to say “2.75”? That would be even worse false precision and sound even more arrogant!
Why not just “about three”, so you don’t sound stuck up like that?
Say, how come you sound all Texan when you get excited?
Because then them sumbutches’d get on muh case for exaggeratin’!!!
So now you’re going to talk about the weird events in Asia?
Wah thuhail not?
We’ll talk about it after the commercial break
What was that all about?
Man’s got t’earn a livin’
OK, so you have this sensitivity number pinned down, and so you know more or less how much co2 or equivalent would cause so much heating? But how much is too much?
“Warming” is better than “heating” here… It’s an important distinction.
That said, that’s the part that is what you might call “unsettled”. There’s been an international consensus on the political side that we ought to avoid so much climate change that it is “dangerous”, which brings us to what people are starting to call “climate disruption”. But at this point it gets out of physical science and a whole lot of other stuff kicks in.
Like what, for instance?
There’s ecology and wildlife management. There’s agriculture. There’s water supplies. There’s public health. There’s flood control. There’s tourism. There’s shipping. Lots of really big systems developed in a stable climate and need to ask themselves what will happen to them. And all the other systems will change too. And all of this will feed back through the economy and back into energy demand.
Many major systems natural and artificial are adapted to a stable climate
All that from a couple of degrees?
Well, a lot of people ask that question. Some folks just argue, look how as soon as we got air conditioning, how so many people moved out of the northern areas and into the southern areas in the US. The guy who first said people might warm up the planet, Arrhenius, was a Swede, and apparently he thought this would be a beneficial side effect of progress. Lots of people think that’s right.
But consider that only 5C separates the present world from the ice age. As I explained last time, for the past several thousand years the temperature has apparently been extremely steady.
A lot of other changes come along with the smallish-sounding temperature change
Remember that I’m trying to say it isn’t the warming that causes the change. The warming is just part of the change. You might even say the climate disruption causes the warming.
Wait, what was that about several thousand years? The famous “hockey stick” only goes back a few hundred years, maybe a thousand, right?
Yeah, but there’s plenty of evidence it has been cooling gradually for about eight thousand years from the interglacial peak.
You mean it was hotter eight thousand years ago?
Yup, pretty much everybody agrees to that.
So why all the excitement to prove that the Medieval Warm Period was warmer than today, when climate science already admits there is a precdeent to being warmer than today in the geologically recent past?
That is a fine question, and one which I for one have no answer!
But if it’s recently been warmer than this, why worry at all? I mean, who is to say today’s temperature is better than some other temperature?
A reasonable question, one of the better ones in the skeptics’ quiver, yet one with many answers.
First of all, there’s the temperature, but there is also the rate at which it changes. It’s really the rate of change where we are getting into territory that nature doesn’t normally see. Second, as I said last time, the temperature isn’t really the problem; it’s just a measure of the problem.
When climate changes slowly, both artificial and natural systems adapt without really even making a big deal of it. Skating on the canals comes in and out of fashion in Holland over the centuries, vineyards start up or fail here and there, but these are tiny, slow, incremental changes. Whereas no, we are talking about rapid climate change, getting faster and faster with each decade.
So to some extent, it is the rate of change that matters. But then there is the total change, which matters a lot for sea level rise, and some other things like mountain runoff and so on. 8000 years ago, we didn’t have megacities near the shorelines. Nor did we have cities in places like Phoenix or Las Vegas.
Well, there weren’t any cities by modern standards, were there?
No, not really. Two hundred years ago there were no cities of a million people. Now we have dozens of swaths of city that have ten million or more. So in terms of how we organize ourselves, everything has changed very recently. Modern civilization has never seen a period of moderate natural climate change, never mind super-accelerated change.
The anticipated rates of change are far outside human experience and are almost unheard of in the entire geological record.
ALMOST unheard of?
There were a couple of weird events that seem connected to abrupt climate change, the most recent being about 55 million years ago. Here, look:
The event saw global temperatures rise by around 6°C (11°F) over 20,000 years, with a corresponding rise in sea level as the whole of the oceans warmed. Atmospheric carbon dioxide (CO2) concentrations rose, causing a shallowing of the lysocline. Regional deep water anoxia may have played a part in marine extinctions.
This was about the time of the first mammals. A very long time ago. Nothing like that since then, and here we are looking to do that in a century or two, not 20,000 years.
Changes in GMST of a few degrees in the geologic record are associated with major rearrangements of nature
OK, so this brings us back to the big question. How much warming is dangerous?
Or, really, how much warming will correspond to a dangerous level of climate disruption?
Yep, that’s the real question alright. We know how to connect CO2 to warming, give or take a factor of two. We know that 5 C or 6 C on a global scale is huge. But we don’t know where the danger point is.
Wait, wasn’t everybody saying 2 C is the “limit posed by science”, just last fall before the Copenhagen blowout?
A lot of people were saying that, and some of them were scientists. I’m not sure they should have, though, because we don’t really know where that danger point is.
So it could be 3 C or 4 C, giving us way more time?
Yes, Hans Joachim Schellnhuber, a man I admire greatly, was one of those talking about the 2 C limit, and he admitted as much in a recent article.
SCHELLNHUBER:From today’s scientific perspective, we could possibly live with a warming of two to three degrees. … The overwhelming majority of climatologists assume that a global temperature rise of four degrees would be an immensely dangerous route that we should avoid at all costs.
DER SPIEGEL: Why then have you, as one of the creators of the two-degree target, imposed such a magical limit to which all countries must slavishly adhere?
SCHELLNHUBER: Politicians like to have clear targets, and a simple number is easier to handle than a complex temperature range. Besides, it was important to introduce a quantitative orientation in the first place, which the 1992 Framework Convention on Climate Change managed to elegantly wangle its way out of. And let’s be honest: Even if we aim for the two-degree target, we’ll end up somewhat higher. Whenever there’s a speed limit, most drivers tend to go a little faster.
Hans von Storch objects vehemently: “I would say, this is pretty shocking, and clearly non-Mertonian: Scientific assertions taylored according to political utility.”
And here we see the rock and the hard place yet again, the dilemma between clarity and effectiveness that the late and lamented Stephen Schneider was the first to discuss publicly. In this case, trhough, von Storch has a strong case. I felt all through the run-up to Copenhagen that this claim needed some sort of caveat.
The truth is, 2 C is the lowest we could possibly have gotten, and 2 C is already possibly dangerous.
The reason, again, is not that 2 C of warming is an issue. It is that 2 C of warming will be accompanied by many other changes. 2 C is a measure of the problem, but is not actually the problem.
We don’t actually know the threshold of dangerous human interference in climate.
Aha, so you guys really are alarmist chicken littles, right? We have decades to get our act together!
Again, again, and yet again. We have to say it until it bores us to tears, and then maybe the message will get through. Uncertainty cuts both ways.
Uncertainty cuts both ways. It’s possible that the threshold of dangerous climate change is lower than 2 C. Suppose it were around 0.7 C for instance?
But… Isn’t that about where we are now?
That’s ridiculous. That’s a third of what they were saying at Copenhagen. And even that was sort of made up just to get people moving! what possible evidence could you have for 0.7 C being dangerous?
Well, there’s this for instance…