[vitaminj]

This hypothetical "fixed amount" of money idea is a bit disingenuous in my opinion, especially since the methods for funding the proposed solutions are very different. The way governments are tackling climate change is primarily through regulation (ie, limiting carbon emissions) - the costs of which will eventually be passed on to the consumer by industry.

The fixed amount of money concept assumes that solving the other problems (eg. AIDS, 3rd world health, etc) are realistic opportunity costs for tackling climate change... but I don't think people would (in aggregate) willingly spend the money saved from climate change regulation on solving these other problems. They'd probably just buy more stuff for themselves.

The equivalent scenario would be if governments taxed people the same amount as the cost of regulation - and that is a tad unrealistic.