In 2007, the IPCC released the Fourth Assessment Report, a summary of the (then-) latest science on climate change. The short version of that report was basically "we're screwed". Now, with less than two weeks to go until the world meets in Copenhagen, the scientists who worked on that report have released their own followup, The Copenhagen Diagnosis. The short version? We're in deep, deep shit.
The core problem is that emissions are still rising - and at rates consistent with the upper end of IPCC modelling. This means that where the IPCC predicted that we were on track for 1.4 degrees of warming, we're now looking at between 4 and 7 degrees. At the same time, we're looking at about twice the sea-level rise projected by the IPCC, a much faster decline in ice coverage, and a much greater chance of hitting regional tipping points which will accelerate the process.
The authors use a carbon budget method to estimate when emissions must peak. Allowing for a total budget of 1000 Gigatons - a figure which has a 75% chance of avoiding the 2 degrees of warming considered "dangerous" - shows that emissions must peak soon, and the later they peak, the sharper the required decline to avoid disaster:
The graph shows the problem of sustainability in a nutshell: safe carbon emissions are a limited resource, and without a radical decarbonisation of the global economy, we are trading off our living standards against those of our children. And that is neither moral or acceptable.