Nature 493, 79–83 (2013)

For more than ten years, international climate debate has focused on how to keep global warming below 2 °C. Despite many scenario analyses, cost estimates of achieving such a target remain a challenge, due to a number of poorly quantified uncertainties.

Joeri Rogelj worked with colleagues at the International Institute for Applied System Analysis, Laxemburg, Austria, to generate the cost distributions of limiting transient global temperature increase to below specific values. They did this by considering uncertainties in geophysical, technological, social and political factors. They found political choices that delay mitigation have the largest effect on the cost distribution, followed by geophysical uncertainties, social factors influencing future energy demand and, lastly, technological uncertainties surrounding the availability of options for greenhouse-gas mitigation.

They conclude that, as it is unlikely a global agreement on climate will be reached before 2020, national and local governments need to scale-up voluntary actions and choose policies that lower growth in energy demand well before then, to safeguard the potential achievement of the 2 °C target.