Matt Yglesias is worried about what climate change will do to poor farmers in the developing world:

Farmers have particular land and particular crops they’re accustomed to growing. When the climate shifts, they’ve got a problem. Initially it won’t be an insurmountable problem for farmers in rich countries who’ll be able to draw on a lot of technical resources to try to adapt. But for poor peasants in the developing world, their livelihoods will be ruined quite rapidly.

My understanding is that, sadly, this is true: climate change will have its most damaging effects on countries that are closer to the equator.  The vast majority of these countries are poor.  Yglesias goes on:

[I]t’s worth attending to the problems of the third world and the ethical issues it raises. I doubt many members of the Chamber of Commerce would, if faced with a starving Namibian family on their front doorstep, just refuse to give them any food and say “hey, I’m greedy, get over it.” But when the climate shifts, there will be crop failures and famines and people will die. And the people preventing action to stop that outcome are doing it because it would be financially inconvenient. So how different is that?

The starving family on the doorstep example greatly understates the complexity of the ethical challenge that climate change poses.  Any climate change mitigation policy that actually succeeds in slowing climate change by enough to have a noticeable effect on the well being of subsistence farmers in the developing world will significantly retard economic growth around the world (global collective action is required for any climate change policy to work).  Unfortunately, this is bad for residents of developing countries because it reduces the export demand for their products, making it more difficult for them to rise out of poverty.

So the ethics of the effect of climate change on farmers in poor countries ends up hinging on a comparison of the cost of climate change with the cost of slower economic growth.  Because of all the uncertainties in the science (granting that there’s scientific consensus about the existence of global warming, the exact amount of warming and the extent of the future damages caused by warming are not clear), this is a difficult calculation to make.

Yglesias’s example does help to illustrate that there are moral demands upon the world’s privileged to help the world’s poor, even if the poor are far away.  But the best way to meet this demand is to donate money to charity, or perhaps to lobby for increased legal immigration and an end to farm subsidies (which indirectly hurt poor farmers).  There are just too many uncertainties for climate change action to be a sensible way of fulfilling our moral obligation to help the poor.