Climate–society feedbacks and the avoidance of dangerous climate change

Abstract

The growth in anthropogenic CO₂ emissions experienced since the onset of the Industrial Revolution is the most important disturbance operating on the Earth’s climate system¹. To avoid dangerous climate change, future greenhouse-gas emissions will have to deviate from business-as-usual trajectories². This implies that feedback links need to exist between climate change and societal actions. Here, we show that, consciously or otherwise, these feedbacks can be represented by linking global mean temperature change to the growth dynamics of CO₂ emissions. We show that the global growth of new renewable sources of energy post-1990 represents a climate–society feedback of ∼0.25% yr⁻¹ per degree increase in global mean temperature. We also show that to fulfil the outcomes negotiated in Durban in 2011, society will have to become ∼ 50 times more responsive to global mean temperature change than it has been since 1990. If global energy use continues to grow as it has done historically then this would result in amplification of the long-term endogenous rate of decarbonization from −0.6% yr⁻¹ to ∼−13% yr⁻¹. It is apparent that modest levels of feedback sensitivity pay large dividends in avoiding climate change but that the marginal return on this effort diminishes rapidly as the required feedback strength increases.