Implications of Earth system tipping pathways for climate change mitigation investment

Abstract

AbstractComplex Earth systems under stress from global heating can resist change for only so long before tipping into transitional chaos. Convergent trajectories of change in Arctic, Amazon and other systems suggest a biosphere tipping point (BTP) in this mid-century. The BTP must be prevented and therefore offers a hard deadline against which to plan, implement, monitor, adjust and accelerate climate change mitigation efforts. These should be judged by their performance against this deadline, requiring mitigation investments to be compared and selected according to the unit cost of their dated mitigation value (tCO2edmv) outcomes. This unit of strategic effectiveness is created by exponentially discounting annual GHG savings in tCO2e against a dated BTP. Three proof of concept cases are described using a BTP in 2050 and a 10% discount rate, highlighting three key ways to prevent the BTP. The most reliably cost-effective for mitigation, and richest in environmental co-benefits, involves protecting high carbon-density natural ecosystems. Restored and regenerating natural ecosystems also yield abundant environmental co-benefits but slower mitigation gains. Improving choice awareness and building capacity to promote decarbonisation in all economic sectors is cost-effective and essential to meeting national net zero emission goals. Public mitigation portfolios should emphasise these three strategic elements, while private ones continue to focus on renewable energy and linked opportunities. Further research should prioritise: (1) consequences of an Arctic Ocean imminently free of summer sea ice; (2) testing the tCO2edmv metric with various assumptions in multiple contexts; and (3) integrating diverse co-benefit values into mitigation investment decisions.