Federal Coordinating Lead Author:
Jeremy Martinich, U.S Environmental Protection Agency
Chapter Lead:
Jeremy Martinich, U.S Environmental Protection Agency
Chapter Authors:
Benjamin DeAngelo, National Oceanic and Atmospheric Administration
Delavane Diaz, Electric Power Research Institute
Brenda Ekwurzel, Union of Concerned Scientists
Guido Franco, California Energy Commission
Carla Frisch, U.S. Department of Energy
James McFarland, U.S. Environmental Protection Agency
Brian O'Neill, University of Denver (National Center for Atmospheric Research through June 2018)
Review Editor:
Andrew Light, George Mason University
USGCRP Coordinators:
David Reidmiller, Director
Christopher W. Avery, Senior Manager

Reducing Risks Through Emissions Mitigation

Current and future emissions, and thus emissions mitigation actions, are crucial for determining future risks and impacts. The scale of risks that can be avoided through mitigation actions is influenced by the magnitude of emissions reductions, the timing of those emissions reductions, and the relative mix of mitigation strategies for emissions of long-lived GHGs (namely, CO2), short-lived GHGs (such as methane), and land-based biologic carbon.1 Intentional removal of CO2 from the atmosphere, often referred to as negative emissions, or other climate interventions have also been proposed10,18 and may play a role in future mitigation strategies (see Box 29.3). 

Net cumulative CO2 emissions in the industrial era will largely determine long-term global average temperature change9 and thus the risks and impacts associated with that change in the climate. Large reductions in present-day emissions of the long-lived GHGs are estimated to have modest temperature effects in the near term (over the next couple decades), but these emission reductions are necessary to achieve any long-term objective of preventing warming of any desired magnitude.9 Decisions that decrease or increase emissions over the next few decades will set into motion the degree of impacts that will likely last throughout the rest of this century, with some impacts (such as sea level rise) lasting for thousands of years or even longer.19,20,21

Meeting any climate stabilization goal, such as the oft-cited objective of limiting the long-term globally averaged temperature to 2°C (3.6°F) above preindustrial levels, necessitates that there be a physical upper limit on the cumulative amount of CO2 that can be added to the atmosphere.9 Early and substantial mitigation offers a greater chance for achieving a long-term goal, whereas delayed and potentially much steeper emissions reductions jeopardize achieving any long-term goal given uncertainties in the physical response of the climate system to changing atmospheric CO2, mitigation deployment uncertainties, and the potential for abrupt consequences.11,22,23 Early efforts also enable an iterative approach to risk management, allowing stakeholders to respond to what is learned over time about climate impacts and the effectiveness of available actions (Ch. 28: Adaptation).24,25,26 Evidence exists that early mitigation can reduce climate impacts in the nearer term (such as reducing the loss of perennial sea ice and effects on ice-dwelling species) and, in the longer term, prevent critical thresholds from being crossed (such as marine ice sheet instability and the resulting consequences for global sea level change).27,28,29,30

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