Should the world try to limit global warming to 2 degrees Celsius?

I've argued before that there seems to be a shift in the wind, in that sceptical papers about aspects of global warming are being published, and that real debate is going on at least in the blogosphere, and quick debate, too. It's all much faster than was the case a few years ago, when the doctrine of 'if it's not peer-reviewed I won't read it' was alive and well. And here is a case in point.

Nature published a piece on the first day of this month with the provocative title 'Ditch the 2C warming goal!' For Nature to do this is another straw in the breeze, because it has been a bastion of the orthodoxy, and the 2C target is part of the orthodoxy. The authors, Victor and Kennel, are serious and well-credentialled, and they are not sceptics in the ordinary sense: in fact they are all about limiting emissions, but think that the 2C target is not the away to go.

Why not? First, the goal is effectively unachievable. Owing to continued failures to mitigate emissions globally, rising emissions are on track to blow through this limit eventually… Because it sounds firm and concerns future warming, the 2 °C target has allowed politicians to pretend that they are organizing for action when, in fact, most have done little. Pretending that they are chasing this unattainable goal has also allowed governments to ignore the need for massive adaptation to climate change.

Second, the 2 °C goal is impractical. It is related only probabilistically to emissions and policies, so it does not tell particular governments and people what to do. In other areas of international politics, goals have had a big effect when they have been translated into concrete, achievable actions.

I would agree with their two principal objections, save for the notion that 'rising emissions are on track to blow through this limit eventually', whenever 'eventually' is. And 'massive adaptation'? If it takes a century or two to teach the 2C target, I don't think it's much of a problem, because on the evidence a warmer world is better for nearly all living things. Incidentally, The Pause has just passed its 18th year on the RSS dataset, and various wags are wondering whether it is time for his gap year, or to buy a car, or to join the army…

Of course, an apparently sceptical piece in Nature was bound to get attention from the sceptical side, and it did so at once. At the same time, it was slammed by the bulldogs of the orthodoxy as well, which caused Victor to write a long response at the New York Times website that is worth reading in its entirety. What comes out strongly to me is Victor's annoyance and frustration at the dug-in defence of the orthodoxy, even when it is plain that it is losing ground, and losing effectiveness as well.

Over at RealClimate, another defensive position, Victor and Kennel's work is dismissed: "… the arguments which they present are ill-informed and simply not supported by the facts". Victor is referred to as 'a political scientist' and Kennel as 'a retired astrophysicist', as though they have no status in this debate. In fact, Victor was a Contributing Lead Author of WGIII in AR5 and is an authority on potential climate-change impacts, while Kennel was not only head of the NASA science advisory board but served as the Director of the Scripps marine sciences institution in San Diego. How dare such as they speak against the Book!

Indeed when I read all the stuff, to and fro, what strikes me most powerfully is the righteous indignation theme. That is mercifully absent on Judith Curry's Climate etc website, and she offers an unexpected approach: "So in context of the current UN framework, personally I prefer to keep 2C for now as a policy target. There is simple political reality: the pause, combined with lower sensitivity estimates, are acting to 'kill the cause', i.e. urgent action needed to reduce emissions."

That is a sensitively political position for a scientist to take. Not being one, I think the 2C goal was a piece of doctrinal nonsense from the beginning. It was designed by politicians as something that could be agreed across the world, and scientists have since found all sorts of compelling reasons why it is a good thing. But this is after-the-event stuff. The 2C target has a dozen or more assumptions built into it.

And here is Dr Curry again on why, even though she prefers to keep the goal, she doesn't like it at all:

Here's why I don't like the 2C metric, and it has little to do with the issues raised by Victor and Kennel. The 2C metric is relevant only for the so-called linear model of decision making. Even if we had some understanding and agreement on what state of the global climate was regarded as dangerous, and we knew what to expect from natural climate variability in the 21st century (e.g. solar, volcanoes, ocean circulations), there is very substantial uncertainty in climate sensitivity to increased CO2, and hence the appropriate emissions target to avoid this level of warming. While the methods continue to be refined to determine sensitivity, none fully account for natural internal variability or for unforced 'climate shifts'.

If you read my post last week on the Lewis/Curry paper, you'll know why she is scornful.

All these papers are really worth reading: the original Victor/Kennel, the Victor response, the RealClimate attack, and the Curry reflections. This is one good way a climate change debate can occur. I hope we'll get more and more, and then maybe a real, live human one in Australia, somewhere soon.