I think that Obama made a good point with air pollution, and how improving air quality is an action which improves public health. Air pollution can exacerbate asthma symptoms, yet there isn't evidence that air pollution increases the chance of having asthma to begin with, actually asthma rates have gone up dramatically in urban areas despite air quality improving. The current thinking is that kids grow up in a world that is too . . . clean, without as much exposure to allergens from animals and other sources as folks had in the past when living in rural areas. So, yes, controlling air pollution will be even more important as more kids get asthma, plus it has other negative effects on health.
http://www.scientificamerican.com/article/why-are-asthma-rates-soaring/
Regarding global warming, well, I don't think anybody knows exactly what the effects will be, atmospheric science is complex and not fully understood. If you're a scientist, there is pressure to say that it will be catastrophic (this is also a self-serving argument as it means more funds for climatologists to study the changes), and likewise the politics on each side of the issue is polarized, when in fact we might see a 'middle of the road' effect where there is modest increase in the amount of drought, and maybe some sea level rise, but perhaps not nearly as bad as predicted. It makes a lot of sense to make the transition from gas to battery powered cars as we'll still need petroleum products to manufacture plastics used in all sorts of products, but there isn't the political will on either side of the spectrum to mandate that people in ten years all buy electric cars (though the electricity still mostly comes from coal, the only feasible alternative to replace most of that source of energy is various type of nuclear, some safer than others, with perhaps 20% to 30% coming from renewables.)
In terms of greenhouse gases, China is probably the biggest contributor, and the developing world increasingly will be as well. So, yes, the U.S. can do some to slow the burning of fossil fuels, but the overall trend is in the opposite direction. Even if China went 100% to electric cars, the power still comes from the coal power plants, which something like one comes online in China everyday!
In the end, tackling overpopulation and the empowerment of women (basic education and autonomy) would probably have a much bigger positive impact than any climate change project, and would help the world better cope with climate change in certain areas of the globe.
