We're pretty certain what weather we're going to experience over the next few days and what we're likely to see over the next century. It's less certain what's going to happen over the problematic medium-term.
This week's New Scientist suggests that we might have cracked this mid-term forecasting problem (seems ocean cycles our the best guide to changes here), but that the messages these mid term forecasts are throwing up some issues which might just scupper the current political momentum towards effective measures to drive down average temperatures and limit the volmes of CO2 in the atmosphere.
It seems that we might be in for several years of cooling and possibly a slow-down in overall global warming in around 5 years which is only going to make it harder to convince people to do the right thing. Apparently, the cooler 2008 we're experiencing to date is already driving up the 'global warming is a hoax' stories.
Trouble is, even several years of cooling won't change the longer term trend towards significant warming. It's just going to make us less likely to mitigate.