Abstract
To limit global warming to <2 °C we must reduce the net amount of CO2 we release into the atmosphere, either by producing less CO2 (conventional mitigation) or by capturing more CO2 (negative emissions). Here, using state-of-the-art carbon-climate models, we quantify the trade-off between these two options in RCP2.6: an Intergovernmental Panel on Climate Change scenario likely to limit global warming below 2 °C. In our best-case illustrative assumption of conventional mitigation, negative emissions of 0.5-3 Gt C (gigatonnes of carbon) per year and storage capacity of 50-250 Gt C are required. In our worst case, those requirements are 7-11 Gt C per year and 1,000-1,600 Gt C, respectively. Because these figures have not been shown to be feasible, we conclude that development of negative emission technologies should be accelerated, but also that conventional mitigation must remain a substantial part of any climate policy aiming at the 2-°C target.
Highlights
To limit global warming to o2 °C we must reduce the net amount of CO2 we release into the atmosphere, either by producing less CO2 or by capturing more CO2
We take estimates of fossil-fuel emissions compatible with RCP2.6 from the following: 11 three-dimensional Earth system models (ESMs) used in the Fifth Intergovernmental Panel on Climate Change (IPCC) report[5,12]; an ensemble of simulations made with an Earth system model of intermediate complexity named JUMP-LCM; another ensemble produced with a simple carbon–climate model named OSCAR
This logically follows our approach of always choosing conventional mitigation over negative emissions when the mitigation potential allows it
Summary
To limit global warming to o2 °C we must reduce the net amount of CO2 we release into the atmosphere, either by producing less CO2 (conventional mitigation) or by capturing more CO2 (negative emissions). Out of the four representative concentration pathways (RCPs) assessed by the Intergovernmental Panel on Climate Change (IPCC), RCP2.6 is the only one that likely limits global warming to o2 °C above preindustrial levels[1] Following such a scenario needs a strong reduction in the net amount of fossil CO2 released into the atmosphere by humankind[2,3]. We call the first option (less CO2 production) ‘conventional mitigation’ and the second option (more CO2 capture) ‘negative emissions’ This definition of negative emissions does not distinguish whether carbon dioxide is captured on site or removed from the free atmosphere. Our results suggest that negative emissions are needed even in the case of very high mitigation rates, and that negative emissions alone cannot ensure meeting the 2-°C target
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