The latest global mass extinction is caused by humanity, and most people are no more aware of the damage they do than is a big asteroid on a collision course with Earth. The lesson of the previous five global mass extinctions is that Earth can absorb a lot of damage, and recover once the problem is past. This is not to be complacent, just an observation. People are the problem now, and one long term solution might be gated communities on a vast, regional scale so that the enlightened stay behind barriers, with enough military and technological power to prohibit the release of better yielding crop varieties, so that the world's population stabilizes by way of intermittent famines.
Another alternative is the release of viruses that do not affect the health of affected people, but makes them sterile. This has been publicized by way of Dan Brown's novel 'Inferno'. His understanding of the science is a little shaky, but the basic idea is sound, and has been used experimentally in Australia to control populations of wild foxes.
World history suggests that people living though food shortages are not usually a serious military threat. The time of pussy footing about is drawing to a close.
