If we accept the IPCC 4th Assessment Report as consensus, we get the following conclusions:
9/10 experts agree humans have net warming effect p.4
We are 66% certain human influence has been enough to affect storm patterns p.6
We are 50% certain humans have affected heatwaves and droughts p.6
We are 66% certain we will see drastic climatic events ( cyclones, storms, droughts) p.8
There is a 90% chance we will see increases in temperature extremes p.8
*Probabilities defined on p. 3 of introduction of actual report.
The U.N. Intergovernmental Panel on Climate Change's 4th assessment report (2007) predicts that the sea level may rise between 18 and 59 cm (~ 7-23 inches dividing by 2.54) by 2100 (p.13, summary for policy makers).
So, according to the major consensus view, there is still quite a bit of uncertainty about the effects of global warming, and these consequences are predicted to be much milder than “sea levels rising by more than 20 feet with the loss of the shelf ice in Greenland and Antarctica, devastating coastal areas worldwide” as depicted in ‘An Inconvenient Truth. While this may happen, the time frame is over thousands of years as opposed to the ‘consensus’ view for the next century.
What economists must do then, is take this consensus science into account, and approximate what the price of carbon should be to limit economic damages from CO2. This level will be achieved where the marginal cost of reducing carbon emissions is equal to the benefits of decreased damages from climate change in the future.