Grant: Discovery Grants Program - Individual

One day, perhaps this decade or potentially far into the future, human emissions of greenhouse gases will peak and begin to decline. Sometime thereafter the Earth system will enter a transitional phase between the rising CO2 concentrations, characteristic of our present era, and the falling concentration of CO2 characteristic of zero emissions scenarios. Idealized experiments using complex climate models suggest that global average temperature will nearly stabilize following cessation of these emissions, even as CO2 concentration falls. However, many questions remain about the transition to a net-zero world and climate after net-zero is achieved, including: how will climate evolve at the regional scale? What will the effect of greenhouse gases besides CO2 be? And what effect will falling CO2 concentrations have on vegetation? Concurrently these zero emissions effects have been studied mostly from idealized numerical experiments where emissions suddenly drop to zero, while very few studies have examined a gradual transition to zero emissions. To help close these gaps in the climate science literature I propose four subprojects. In Subproject-I climate milestones on the road to net-zero emissions will be defined and robust methods used detect that a milestone has passed will be developed. Climate milestones include peak CO2 emissions, peak CO2 concentration, a slowdown in global warming and the beginning of global cooling. Subproject-II will use the archived results of climate model experiments to explore what effect the combination of dropping CO2 concentrations and stable global temperatures has on the simulated terrestrial biosphere in general, and the stability of the Amazon and desertification in particular. Subproject-III will develop new climate model experiments to account for the effect of CH4, N2O, synthetic greenhouse gases, and aerosols on zero emissions commitment, and will develop methods to separately account for the effects of agriculture and industrial activities on zero emissions commitment. Subproject-IV will explore deeper into the physical and biogeochemical foundations of remaining carbon budgets to attempt to discover how the relationship that remaining carbon budgets are based on emerges from simpler processes. Together these subprojects will map out future climate milestones on the pathway to net zero emissions, explore the poorly studied consequences of decarbonisation (such as falling atmospheric CO2 concentration as warming continues), expand the understanding of zero emissions commitment to realistic future scenarios, and delve deeper into the foundations of the cumulative emissions framework of climate change mitigation. The underlying aim of the proposed research program is to inform climate policy by mapping out the likely course of climate milestones, so that the counter-intuitive effects of decarbonization on the Earth system do not derail climate change mitigation efforts in the coming decades.