By Bjørn Lomborg (via his Facebook page)
About a quarter of all deaths in the developing world comes from mostly easily curable, infectious diseases.
The biggest environment problem, by far measured in human deaths, is air pollution.
Global warming, which creates a lot of attention, is on an entirely different and smaller level. The World Health Organization estimate (a very maximal estimate) is about one-fortieth of the deaths from air pollution. Even if you assume all deaths from floods, droughts and storms, the number is an even smaller two-hundredth of air pollution.
And no, the number of deaths from global warming won’t increase, but more likely decrease over time, as many infectious deaths will disappear because of increasing wealth, and because fewer cold deaths will increasingly outweigh increasing heat deaths.
Source: Communicable deaths and air pollution deaths from Global Burden of Disease, doi:10.1016/S0140-6736(12)61766-8.
Infectious diseases are about 10m of 52.6m global deaths, and 9.2m of 39.7m developing world deaths.
Air pollution lies between 3.5m and 6.9m (indoor and outdoor air pollution is somewhat overlapping, because indoor air pollution contributes 16% to global outdoor air pollution, and because there is no good estimate of how close most people stay to homes when outside). Here, just using the mean, which is likely an underestimate.
WHO global warming estimate is 141,000 deaths (http://www.who.int/mediacentre/factsheets/fs266/en/). Lower estimate is just 28,266/year for the past decade , using estimates of deaths from flooding, droughts, heatwaves and storms, and assume they’re all from climate change, (http://www.csccc.info/reports/report_23.pdf).
Long-term development of deaths from Richard Tol’s chapter for my upcoming book, How Much have Global Problems Cost the World? A Scorecard from 1900 to 2050 (http://www.cambridge.org/us/academic/subjects/economics/economic-development-and-growth/how-much-have-global-problems-cost-world-scorecard-1900-2050).
For now, see the estimates from Bosello et al. for 2050 showing global warming *saving* about 850,000 lives (1.76m saved from cold, vs 820,000 more dead from heat), http://www.sciencedirect.com/science/article/pii/S0921800905003423.