The report from Kevin Anderson and colleagues at the Tyndall Centre outlining how the UK could "do its fair share" in keeping global atmospheric concentrations of greenhouse gases below 450ppm looks like a serious, professional bit of work (press release here, full report -- a 175 page pdf -- here, sensational Guardian coverage here). It charts a route to reducing UK emissions by 70% by 2030, with greater cuts beyond that.
Also interesting is a report in Platts that the Bush administration "may announce as early as next week a goal of stabilizing carbon dioxide levels in the global atmosphere at 450 parts per million by the year 2106".
This rumour, if proved true, looks like a canny bit of political triangulation: seize your opponents' issue and sound visionary while not actually committing to anything that requires real action or pain. 2106 is like 110 years from now, man. Dave Hamilton of the Sierra Club is reportedly of this view, saying that the stabilisation target should be reached much sooner, and by 2050 at the latest.
But Jon Gibbins argues it is not as simple as that: atmospheric concentrations will actually have to be lower than 450ppm in 2050 if (barring what he thinks are unlikely developments in capacity to draw down CO2 from the atmosphere at an accelerated rate) there is to be a chance of stabilising at that level by 2106. If correct, this would mean that if the Bush administration were serious about their target they would have to act even more urgently than even their harshest critics suggest -- a corollary that may have escaped them so far.
The reasoning here is simpler than I may have made it sound. An explanation from Jon is attached, with his kind permission.