Tim Lenton published on May 4,2011, in Nature 473, 7 (2011) | doi:10.1038/473007a the article
2 °C or not 2 °C? That is the climate question
Editorial introduction: Targets to limit the global temperature rise won't prevent climate disruption. Tim Lenton says that policy-makers should focus on regional impacts.
Key Statement: I suggest that the UNFCCC be extended. The climate problem, and the political targets presented as a solution, should be aimed at restricting anthropogenic radiative forcing to limit the rate and gradients of climate change, before limiting its eventual magnitude.
All this reminds me on the Hartwell paper, but I do not see a reference to this paper.
A more complete text is published as Focus Article
Lenton, T.M., 2011: Beyond 2°C: Redefining dangerous limate change for physical systems
in WIRES Climate Change 2, 451-461