Is the US-China climate change agreement a big deal? Yes and no. It is quite a significant and consequential political achievement. But it is not particularly important in its direct effect on greenhouse gas emissions.
Whether the agreement ultimately matters to the fate of the world will depend on whether its political impact turns out to be catalytic, spurring not just other political agreements between the world's leading greenhouse gas emitters but - quickly - aggressive reductions in greenhouse gas pollution.
First, as to the agreement's political significance. Progress in international climate negotiations and even in US domestic policy has long been handcuffed by disagreements about the allocation of responsibility for action among rich and poor countries, and particularly between the US and China.
China clearly has the upper hand in this debate. It is plainly true that the industrialised countries are responsible for the overwhelming share of carbon accumulation in the atmosphere. It is also plainly true that the richer countries have more capacity to make needed investments to reduce greenhouse gas emissions. And, it should be obvious that facing a genuinely global threat, the rich need to do more than the poor, just as rich families need to pay more in taxes than poor families to pay for schools, police, hospitals, roads and other public goods.
However, there are certain countervailing realities. The most important is that, thanks to its spectacular growth over the last several decades, China is now the world's largest emitter of carbon (though it remains behind the US and other rich countries on a per capita basis). Achieving the needed radical reductions in greenhouse gas pollution will require major action from China (and India, and other developing countries).
Additionally, the US-China trade balance has become so unbalanced that it is economically challenging to impose unilateral costs on US manufacturers (unless they are protected against more carbon-intense imports) and an even bigger problem in terms of domestic US politics.
Against this backdrop, a deal - even a voluntary one - in which both the US and China agree to responsibility for controlling their greenhouse gas emissions is a political breakthrough. It suddenly makes it possible to make progress in world climate talks, and it removes one of the biggest political impediments to the US taking meaningful action on its own and to signing onto a global agreement.
The problem is that this politically significant agreement is incredibly unambitious when it comes to actually reducing greenhouse gas pollution. In the deal, the US agrees to reduce carbon emissions 30 percent from its 2005 level by 2030, and China agrees to keep its 2030 emissions level the same as 2005. This is far too little, and far too slow.
On the US side, the promised reduction is not only not enough, it's pretty close to what the US is going to achieve anyway. The Obama administration has been far too slow and modest in policy-making, but it has significantly increased auto fuel efficiency standards, and it is working now on rules that will also reduce emissions from coal plants and hopefully natural gas, as well. Additionally, market forces are now kicking in so that some meaningful reductions are inevitable without any government intervention; investments in energy efficiency are cost-effective right now throughout the economy - meaning it is cheaper to invest in insulation, better windows, better lighting, more efficient industrial commitment, etc, than to pay increased electricity costs. And, wind and solar energy output is soaring and costs plummeting. In many cases already, wind is cheaper than coal.
Roughly the same holds on the Chinese side. Although the government should be credited for pushing out support for solar and wind energy development, simple cost accounting is now increasingly favouring efficiency, wind and solar over fossil fuels. Many analysts believe China is already on track to achieve exactly the level promised in the US deal, without any or much additional government action.
There's not really any mystery about what the world needs to do to avert catastrophic climate change, and there isn't much difference between the national and global agendas. We need massive investments in energy efficiency and renewable energy. The good news is that, over time, these investments will lower our energy costs. The sun and the wind are free; we just to have to get better at harvesting their energy - major strides have already been made in the last decade. We need large-scale transfers of know-how (intellectual property) and resources from rich to poor countries to speed the transition to a carbon-free future, as well as to help poorer countries adapt to the serious costs that even moderated climate change will impose. And, we have to do all this quickly, because energy savings today are much more important than those in 2045, or even 2030.
All of this is doable, but it won't happen on its own. That's why we need binding intergovernmental commitments. The US-China deal doesn't do much to reduce greenhouse gas pollution on its own; we have to hope that it does pave the way for future political deals to do just that.