Of course, if the costs exceed the benefits of, say, genuinely trying to solve global hunger, or to eradicate malaria, or to ensure clean water, then they're not worth doing either. These "pressing problems" hardly ever end up pressing enough to fit cost-benefit schemes because many of the values in question cannot be captured in quantitative terms, or because certain human lives are discounted vis-à-vis other human lives. The future - given rising uncertainty the further we go into it - is always discounted vis-à-vis the present. So, the general climate change argument, depending as it does on some sense of responsibility to the future, faces an uphill battle from the get-go if our only tool of analysis is cost-benefit. That battle is simply assumed into the models.
Assuming our grandchildren’s welfare is just as valuable as our own provides a metric to measure the value of investments for the future: devoting X percent of the current generation’s income to forestall global warming would be a good deal if it produced a benefit amounting to more than X percent of that future generation’s income.
Such notions of intergenerational equity underpin the 2006 Stern Review on the Economics of Climate Change, a British study that marked a turning point in the debate, stressing the enormous cost of delaying preventive action. It projected that avoiding large-scale environmental damage, starting in the second half of this century, justified starting to spend immediately 1 percent of the world’s income — about $700 billion this year — to cut carbon emissions.
However, farsightedness, as in saving for a rainy day, went out of fashion a long time ago. People often sacrifice the future to the present. We may love our children and grandchildren. But since they can’t vote, we stiff them in the public sphere: poverty is deeper among children than the elderly, yet public spending on the elderly vastly outstrips spending on the young. In Florida, “I’m spending my children’s inheritance” is a popular bumper sticker. Even among very green Western Europeans, polls show that the older people get, the less they are willing to pay to reduce carbon emissions....
Skeptics have used these arguments to make a case against aggressive efforts to address global warming. A group of respected, mainly American economists signed the so-called Copenhagen Consensus, stating that efforts to address global warming, such as the Kyoto Protocol, had “costs that were likely to exceed the benefits.” It was better to spend money on some of the world’s other pressing problems.
The author of the piece suggests this at the end,
The best case for bold action now is that it provides insurance against the chance of an unfathomably grim future of large-scale environmental disruption, widespread species extinction, worldwide hunger. All of that might come to pass if the world chooses to do nothing. Averting that kind of future is worth quite a lot of investment today.But how does that serve as a reason for economists, the ones who have an inordinately (and unjustifiably) tight grasp over policy questions in the US government? It doesn't. The disaster scenario has a fairly high level of plausibility, specious accusations against supposed liberal, environmental fear-mongering notwithstanding (here and here and here, for example). These people use the language of "environmentalists are..." when what is really meant - though they may not know it themselves - is "a few of my straw man environmentalists are...." Good arguments depend upon charitableness towards opponents' views - none of these come close. The real philosophical, ethical, scientific, and even economic debates are more sophisticated, complex, and momentous.
The author of the present article, in the end, makes a series of ethical claims. We can attach economic importance to them - environmental disruption also entails economic losses - but they are nonetheless primarily ethical. Yet, here we are, generally poor deliberators, having subsumed ethical deliberation under the category of diminishing investment returns for so long that we've impoverished our own capacity to try make sense of and wise decisions about the future. And that's really odd because without a robust future, whether short or long term, our lives are pretty pointless.