Climate change: do we know enough for policy action?

The climate change problem must be thought of in terms of risk, not certainty. There are many well-established elements of the problem that carry considerable confidence whereas some aspects are speculative. Therefore, the climate problem emerges not simply as a normal science research issue, but as a risk management policy debate as well. Descriptive science entails using empirical and theoretical methods to quantify the two factors that go into risk assessment: "What can happen?" and "What are the odds?" (Probability x Consequences). Policymakers should, in turn, take that information and use it to make value judgments about what is safe, what is dangerous, what is fair. To make these judgments, policymakers need to know the probabilities that experts assign to various possible outcomes in order to make risk management decisions to hedge against unsafe, dangerous and unfair outcomes. The climate debate needs to be reframed away from absolute costs--or benefits--into relative delay times to achieve specific caps or to avoid crossing specific agreed 'dangerous' climate change thresholds. Even in most optimistic scenarios, CO2 will stabilize at a much higher concentration than it has reached today, and temperature will rise accordingly. It will take even longer for sea level rise from thermal expansion and the melting of polar ice to occur, but what is most problematic is that how we handle our emissions now and in the next five decades preconditions the sustainability of the next millennium.