There's a lot of talk in the media about how groundbreaking and ambitious the US-China climate deal is, but is that true? Here's how American economist Tyler Cowen (a conservative, but a mainstream figure and certainly not a 'denialist') greeted the news:

Overnight, Cowen elaborated on this statement on his blog Marginal Revolution:

...if you look at the history of air pollution, countries clean up the most visible and also the most domestically dangerous problems first, and often decades before solving the tougher issues. For China that highly visible, deadly pollutant would be Total Particulate Matter, which kills people in a rather direct way, and in large numbers, and is also relatively easy to take care of.  (Mexico for instance has been getting that one under control for some time now.) The Chinese people (and government) are much more worried about TPM than about carbon emissions, which is seen as something foreigners complain about.  Yet TPM is still getting worse in China, and if it is (possibly) flat-lining this year that is only because of the economic slowdown, not because of better policy.

When will China cap carbon emissions? “Fix TPM and get back to me in twenty years” is still probably an underestimate. Don’t forget that by best estimates CO2 emissions were up last year in China by more than four percent. How many wealthier countries have made real progress on carbon emissions?  Even Denmark has simply flattened them out, not pulled them back.

The Chinese really are making a big and genuine effort when it comes to renewables, it is just that such an effort is dwarfed by the problems mentioned above.

if you look at the history of air pollution, countries clean up the most visible and also the most domestically dangerous problems first, and often decades before solving the tougher issues.  For China that highly visible, deadly pollutant would be Total Particulate Matter, which kills people in a rather direct way, and in large numbers, and is also relatively easy to take care of.  (Mexico for instance has been getting that one under control for some time now.)  The Chinese people (and government) are much more worried about TPM than about carbon emissions, which is seen as something foreigners complain about.  Yet TPM is still getting worse in China, and if it is (possibly) flat-lining this year that is only because of the economic slowdown, not because of better policy.

When will China cap carbon emissions?  “Fix TPM and get back to me in twenty years” is still probably an underestimate.  Don’t forget that by best estimates CO2 emissions were up last year in China by more than four percent.  How many wealthier countries have made real progress on carbon emissions?  Even Denmark has simply flattened them out, not pulled them back.

The Chinese really are making a big and genuine effort when it comes to renewables, it is just that such an effort is dwarfed by the problems mentioned above.

- See more at: http://marginalrevolution.com/#sthash.r4F8miD2.dpuf

if you look at the history of air pollution, countries clean up the most visible and also the most domestically dangerous problems first, and often decades before solving the tougher issues.  For China that highly visible, deadly pollutant would be Total Particulate Matter, which kills people in a rather direct way, and in large numbers, and is also relatively easy to take care of.  (Mexico for instance has been getting that one under control for some time now.)  The Chinese people (and government) are much more worried about TPM than about carbon emissions, which is seen as something foreigners complain about.  Yet TPM is still getting worse in China, and if it is (possibly) flat-lining this year that is only because of the economic slowdown, not because of better policy.

When will China cap carbon emissions?  “Fix TPM and get back to me in twenty years” is still probably an underestimate.  Don’t forget that by best estimates CO2 emissions were up last year in China by more than four percent.  How many wealthier countries have made real progress on carbon emissions?  Even Denmark has simply flattened them out, not pulled them back.

The Chinese really are making a big and genuine effort when it comes to renewables, it is just that such an effort is dwarfed by the problems mentioned above.

- See more at: http://marginalrevolution.com/#sthash.r4F8miD2.dpuf

What's interesting is that the commentary I have seen in support of the deal does not really deny these arguments. Instead, it leans heavily on the symbolism of the agreement, so in a way actually reinforces Cowen's point. It's just that Cowen thinks it is merely symbolism, whereas others think the symbolism itself is the main point. Here's Paul Krugman:

...what we’re getting here is more a statement of principle than the shape of policy to come. But the principle that has just been established is a very important one. Until now, those of us who argued that China could be induced to join an international climate agreement were speculating. Now we have the Chinese saying that they are, indeed, willing to deal — and the opponents of action have to claim that they don’t mean what they say.

Brian Merchant at Grist:

It's fraught with symbolism. The two biggest polluters, who have never agreed on much of anything about climate change at all, are issuing a deal that seriously reflects the scope and depth of the problem. The agreement will have a profound effect on the international community, and it's already sending cheers through the climate circles around the world. The two immobile pillars propping the up the bulk of the world's fossil fuel infrastructure finally feel like they've budged.

James Fallows:

As the collapse of the Copenhagen climate talks five years ago showed, the rest of the world is likely to say, "To hell with it" if the two countries at the heart of this problem can't be bothered to do anything....This new agreement does not mean that next year's global climate negotiations in Paris will succeed. But it means they are no longer guaranteed to fail.

And finally, here's the Council on Foreign Relations' Michael Levi on the symbolism for great-power relations:

China has typically gone out of its way to assert its independence in anything climate-related. That approach would usually have led it to announce major goals like these in a clearly unilateral context – even if they were developed in tandem with the United States. Rolling them out together with the United States says that China is increasingly comfortable being seen to act as part of an international effort.

Indeed that may be part of the point here. Xi appears at least somewhat sensitive to historical patterns of conflict between established and rising powers. Amidst broad tensions between the United States and China, climate change is increasingly an area of relatively constructive dialogue, which makes it worth highlighting. A joint announcement does exactly that.