Fourth National Climate Assessment

Fourth National Climate Assessment
Name	Fourth National Climate Assessment
Caption	Cover of the Fourth National Climate Assessment (2018, Volume II)
Author	U.S. Global Change Research Program; contributors from National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, National Science Foundation, Department of Energy, Environmental Protection Agency
Country	United States
Language	English
Topic	Climate change, climate impacts, climate policy
Publisher	U.S. Global Change Research Program
Pub date	2018–2019
Pages	Multi-volume

Fourth National Climate Assessment is the fourth major synthesis of climate change science and impacts for the United States coordinated by the U.S. Global Change Research Program. The assessment was released in two volumes between 2017 and 2018 and produced a comprehensive appraisal of observed changes, projected risks, and response options linking research from agencies such as the National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, Environmental Protection Agency, and the Department of Energy. It informed federal and state decision-making and interacted with international processes including the Intergovernmental Panel on Climate Change and the United Nations Framework Convention on Climate Change.

Overview

The assessment consolidates peer-reviewed science and agency reports to evaluate contemporary climate hazards, trends, and resilience strategies across the United States. It synthesizes contributions from federal laboratories including Argonne National Laboratory, Oak Ridge National Laboratory, and Lawrence Berkeley National Laboratory and leverages observational networks such as the National Climatic Data Center, Global Historical Climatology Network, and U.S. Geological Survey monitoring programs. The volumes were prepared under the auspices of the U.S. Global Change Research Program with stakeholder engagements involving state governments like California, Florida, and Alaska, metropolitan areas such as New York City and Houston, and tribal nations including the Navajo Nation.

Key Findings

The report concludes that continued emissions of greenhouse gases will cause further warming, sea level rise, and increases in the frequency and/or intensity of extreme events. It documents observed warming trends using datasets from NOAA, NASA's Goddard Institute for Space Studies, and reanalyses used by the European Centre for Medium-Range Weather Forecasts; projects future conditions using models from the Coupled Model Intercomparison Project; and quantifies impacts on sectors including agriculture, health, and infrastructure. It highlights links between emissions scenarios used by the Intergovernmental Panel on Climate Change and projected risks faced by regions such as the Gulf Coast, Northeast United States, Pacific Northwest, and Great Plains. The assessment emphasizes that mitigation aligned with the Paris Agreement temperature goals reduces long-term risks, while adaptation and resilience measures can moderate near-term impacts.

Regional and Sectoral Impacts

Regional chapters synthesize evidence for areas including the Alaska, the Arctic Council-adjacent zones, the Hawaii archipelago, and the U.S. Virgin Islands, and address sectoral vulnerabilities in energy systems, transportation networks, public health, and ecosystems. It documents coastal inundation and erosion affecting communities from Louisiana's wetlands to Maine's shoreline, inland flooding in the Midwest and Mississippi River basin, wildfire and drought stress in the California and Southwest regions, and permafrost thaw in Alaska that impacts infrastructure and Indigenous subsistence tied to communities such as the Aleut and Inupiat. Sector analyses draw on studies by U.S. Army Corps of Engineers, Federal Emergency Management Agency, and the Centers for Disease Control and Prevention to quantify economic damages, health burdens, and ecosystem shifts affecting landscapes like the Great Barrier Reef (as comparative science) and fisheries of the Atlantic Ocean and Pacific Ocean.

Adaptation and Mitigation Responses

The assessment evaluates adaptation strategies including nature-based solutions, engineering defenses, and policy instruments such as carbon pricing and regulatory standards. It reviews mitigation pathways informed by integrated assessment models used by the International Energy Agency, research from Lawrence Livermore National Laboratory, and deployment case studies from states like California and countries such as Germany and China. Recommended responses span land-use planning, grid resilience investments involving Federal Energy Regulatory Commission considerations, public health preparedness coordinated with Centers for Disease Control and Prevention, and conservation strategies promoted by organizations such as The Nature Conservancy and the National Audubon Society. The report underscores co-benefits of mitigation for air quality, referencing work by the World Health Organization on health outcomes.

Methodology and Data Sources

Methodological approaches combined observational analyses, attribution studies, scenario-based climate modeling, and risk-assessment frameworks. Key datasets derive from NOAA temperature and precipitation records, NASA satellite remote sensing products, tree-ring chronologies curated by the International Tree-Ring Data Bank, and socioeconomic projections from agencies like the Bureau of Economic Analysis and the U.S. Census Bureau. Climate projections relied on global climate models participating in CMIP5 and CMIP6 with scenario narratives aligned to Representative Concentration Pathways and Shared Socioeconomic Pathways. Expert elicitation, literature synthesis, and review by the National Academies of Sciences, Engineering, and Medicine informed confidence statements and uncertainty characterizations.

Reception, Criticism, and Policy Influence

The assessment prompted responses across the political spectrum and influenced policy deliberations at the White House, congressional committees such as the House Committee on Science, Space, and Technology, state legislatures, and municipal planning offices. Scientific organizations including the American Geophysical Union, American Meteorological Society, and the Union of Concerned Scientists endorsed the findings. Critiques addressed framing, economic valuation methods, and treatment of uncertainty raised by commentators linked to think tanks like the Heritage Foundation and Cato Institute; independent reviews by the National Academies of Sciences, Engineering, and Medicine and academic authors evaluated robustness and accessibility. The assessment informed adaptation planning in agencies including the Department of Defense, Department of Transportation, and influenced U.S. submissions to the United Nations Framework Convention on Climate Change and implementation considerations for the Paris Agreement.

Category:Climate change in the United States Category:Environmental reports