A while ago I wrote briefly on why the Singularity might not be near and my estimates badly off. I saw it linked the other day, and realized that pessimism seemed to be trendy lately, which meant I ought to work on why one might be optimistic instead: http://www.gwern.net/Mistakes#counter-point
(Summary: long-sought AI goals have been recently achieved, global economic growth & political stability continues, and some resource crunches have turned into surpluses - all contrary to long-standing pessimistic forecasts.)
It doesn't have to turn the Earth into Venus for unusually-rapid climate shifts to destabilize geopolitics badly, exceed system tolerances in infrastructure, consume an ever-growing portion of the economy either by increased loss and waste or in efforts at mitigation, and thereby effectively amp up the power of many other forms of global X-risk (or just contribute directly to X-risk by numerous small factors, none of which would by itself be capable of overwhelming the system, but which collectively undermine it).