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

Actions are currently underway at global, national, and subnational scales to reduce GHG emissions. This section provides an overview of agreements, policies, and actions being taken at various levels.

Long-Term Temperature Goals and the Paris Agreement

The idea of limiting globally averaged warming to a specific value has long been examined in the scientific literature and, in turn, gained attention in policy discourse (see DeAngelo et al. 2017 for additional information9). Most recently, the Paris Agreement of 2015 took on the long-term aims of “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels”.31 These targets were developed with the goal of avoiding the most severe climate impacts; however, they should not be viewed as thresholds below which there are zero risks and above which numerous tipping points occur (that is, a point at which a change in the climate triggers a significant environmental event, which may be permanent). In order to reach the Paris Agreement’s long-term temperature goal, Parties to the Agreement “aim to reach global peaking of GHG emissions as soon as possible . . . and to undertake rapid reductions thereafter.” Many countries announced voluntary, nonbinding GHG emissions reduction targets and related actions in the lead-up to the Paris meeting; these announcements addressed emissions through 2025 or 2030 and took a range of forms.31 The Paris Agreement has been ratified by 180 Parties to the UN Framework Convention on Climate Change, which account for 88% of global GHG emissions.32,33

Achieving the Paris Agreement target of limiting global mean temperature to less than 2°C (3.6°F) above preindustrial levels requires substantial reductions in net global CO2 emissions prior to 2040 relative to present-day values and likely requires net CO2 emissions to become zero or possibly negative later in the century, relying on as-yet unproven technologies to remove CO2 from the atmosphere. To remain under this temperature threshold with two-thirds likelihood, future cumulative net CO2 emissions would need to be limited to approximately 230 gigatons of carbon (GtC), an amount that would be reached in roughly the next two decades assuming global emissions follow the range between the RCP4.5 and RCP8.5 scenarios.9 Achieving global GHG emissions reduction targets and actions announced by governments in the lead-up to the 2015 Paris climate conference would hold open the possibility of meeting the 2°C (3.6°F) temperature goal, whereas there would be virtually no chance if net global emissions followed a pathway well above those implied by country announcements.9

In June 2017, the United States announced its intent to withdraw from the Paris Agreement.34 The statement is available online: https://www.whitehouse.gov/briefings-statements/statement-president-trump-paris-climate-accord/. The earliest effective date of formal withdrawal is November 4, 2020. Some state governments, local governments, and private-sector entities have announced pledges to reduce emissions in the context of long-term temperature aims consistent with those outlined in the Paris Agreement.35,36

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