The Intergovernmental Panel on Climate Change has published the first part of their Fourth Assessment Report, titled "The Physical Science Basis of Climate Change"

 

http://ipcc-wg1.ucar.edu/index.html

 

To summarize the first volume in a single sentence:

 

It is very likely that anthropogenic greenhouse gas increases caused most of the average temperature increases since the mid-20th century

 

Some quick stats:

 

2500+ peer reviewers

800+ contributing authors

450+ lead authors from

130+ countries

6 years of work

 

The NAS conclusions from the TAR were:

 

http://nationalacademies.org/onpi/06072005.pdf

 

The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action.

 

(Edit: Post #3000! I'm officially a Scientist! Yay!)

In Figure SPM-2 on page 4, it states that,

The net anthropogenic radiative forcing and its range are also shown. These require summing asymmetric uncertainty estimates from the component terms, and cannot be obtained by simple addition. {2.9, Figure 2.20}

 

Can someone explain "asymmetric uncertainty estimates"?

I'm not entirely sure but I think the numbers that add into it have certain error margins so they add it all in somehow. "You can't just add up all the numbers."