Hurricane Katrina, adumbrated by models of global warming, was as clear as sign as one needs that global warming is real and a real threat. The time for evaluating risks has really ended-there is vast consensus among experts that global warming is happening and that it is serious.
We need to cut human CO2 emissions to basically only those from breathing (respiration) as, as well as cut other global warming pollutants to as near zero as possible. The government can and must provide incentives to industry to develop and commericialize alternative, clean energy. Other actions will need to be more creative: for example to curb the contribution to global warming by livestock (a surprisingly large percentage), the government ought promote a healthy diet which is relatively red meat free.
Similarly, emergency planning and risk assessments have to use models based on global warming (which most do already) so that we are prepared for future Katrinas.
We must first curb and steady our contributions to global warming and work with all countries of the world to achieve this. Once we have some ability then to forecast the potential severity of global warming effects, we must similarly work with all countries of the world to implement creative proposals (many exist) that could avert the effects of global warming. What we can not do is continue to ignore what innumerable studies and three thousand dead Americans should have taught us, that global warming is happening and we must act.