Closely mirroring the simulations presented over at Climate Interactive, the World Resources Institute just released a detailed paper examining the pledges of Annex I (developed) nations at the most recent climate talks leading up to Copenhagen.
According to the paper, Comparability of Annex/Emission Reduction Pledges (PDF) the current impact of a "successful" Copenhagen agreement (as it stands right now) would more or less condemn the planet to certain doom, amounting on the low end to little more than 10% GHG reduction over 1990 levels by 2020.
Better than nothing, but not enough to make a serious correction in the hockey-sticking of mean global temperatures.
The report is a great look into the complexities of the haggling that is taking place in the negotiation chambers, presenting a comparative analysis which looks at greenhouse gas emissions (both with and without carbon offsets from forestry, etc.) by country over various benchmarks -- 1990 levels, 2000 levels, and 2005 levels.
The good news is that some countries like the UK, have higher targets in place that are contingent upon other Annex I countries (like the U.S.) stepping up to the plate.
Jennifer Morgan of the WRI sums it up:
While emission reduction commitments by these countries could have an important and potentially substantial impact, they will not be enough to meet recommendations of IPCC's Fourth Assessment Report. WRI therefore urges industrialised countries to bring forward more ambitious pledges to reduce their greenhouse gas emissions.