Since there is a lot of uncertainty as to what the negative impact of global warming might be, doesn't it make sense to focus on the people who are dying right now?
It depends on your risk/reward curve, and your probability estimates.
Malaria is unlikely to get much WORSE than it is now. But if you think that global warming has a chance to cause catastrophic damage, two or three orders of magnitude more than malaria is causing today, then you should estimate the probability that you can impact global warming and do the EV calculation.
