Abstract

Oceans and Marine Resources in a Changing Climate describes scientific knowledge of current and projected impacts of climate change and ocean acidification on the physical, chemical, and biological components and human uses of marine ecosystems under U.S. jurisdiction. One of a series of technical inputs for the third National Climate Assessment (NCA) conducted under the auspices of the U.S. Global Change Research Program, it also assesses efforts to prepare for and adapt to climate and acidification impacts on ocean ecosystems across

Executive Summary

The United States (U.S.) is an ocean nation; our past, present and future are inextricably connected to and dependent on oceans and marine resources. Marine ecosystems under U.S. jurisdiction extend from the shore to 200 nautical miles seaward, include waters around U.S. Territories, and span 3.4 million square nautical miles of ocean, an area re- ferred to as the U.S. exclusive economic zone (NMFS, 2009a), which is an area 1.7 times the land area of the continental U.S.. This area encompasses an incredible diversity of species and habitats as well as 11 different large marine ecosystems (LMEs) that provide many important services, including jobs, food, transportation routes, recreational op- portunities, health benefits, climate regulation, and cultural heritages that affect people, communities, and economies across America and internationally every day.

U.S. marine ecosystems and services are increasingly at risk from climate change and other human pressures. A wealth of information documents strong linkages between the planet’s climate and ocean systems as well as changes in the climate system that can pro- duce dramatic changes in the physical, chemical, and biological characteristics of ocean ecosystems on a variety of spatial and temporal scales. Additionally, a growing body of literature provides evidence of the current impacts of increasing atmospheric carbon di- oxide and the associated global warming and ocean acidification on physical, chemical, and biological components of ocean ecosystems. Conversely, relatively little information shows how these climate-driven changes in ocean ecosystems may impact ocean ser- vices and uses, although it is predicted that the vulnerability of ocean-dependent users, communities, and economies increases in a changing climate. In addition, non-climatic stressors resulting from a variety of human activities, including pollution, fishing im- pacts, and over-use, can interact with and exacerbate impacts of climate change. Collec- tively, climatic and non-climatic pressures on marine ecosystems are having profound and diverse impacts that are expected to increase in the future.

Based on current understanding of these linkages between the planet’s climate and ocean systems as well as projections of future changes in the global climate system, the marine ecosystems under U.S. jurisdiction and U.S. interest internationally are likely to continue to be affected by anthropogenic-driven climate change and rising levels of atmospheric CO2. These impacts are set in motion through a collection of changes in the ocean’s physical (e.g., temperature, circulation, stratification, upwelling), chemical (e.g., acidification, nutrient input, oxygen content), and biological (e.g., primary production, species distributions, phenology, foodweb structure, community composition and eco- system functions/services) components and processes. Given the value and U.S. depen- dence on ocean products and ecosystem services found in U.S. and international ocean ecosystems, these climate-driven changes are likely to have significant implications for U.S ocean uses and international activities as well as the communities and economies that depend on them. Effectively responding to these challenges requires mitigating the pace and scope of climate change through concerted efforts to reduce emissions of greenhouse gases and protect and enhance those natural environments that act as car- bon sinks as well as helping species, ecosystems, and the societies that depend on them to adapt to the changes we can no longer avoid.This report was produced by a team of experts as a contribution to the third National Climate Assessment (NCA), conducted under the auspices of the U.S. Global Change Research Program (USGCRP). The report provides an assessment of scientific knowl- edge of the current and projected impacts of climate change and ocean acidification on the physical, chemical, and biological components and human uses of marine ecosys- tems under U.S. jurisdiction. It also provides assessment of the international implica- tions for the U.S. due to climate impacts on ocean ecosystems and of efforts to prepare for and adapt to climate and acidification impacts on ocean ecosystems.

U.S marine ecosystems are inherently connected to U.S. coastal and terrestrial areas through the flow of water from land to sea, the effect of oceans on the physical climate system, the connectivity and movement of species, and the extensive and diverse uses of marine resources and services that occur throughout the Nation. Therefore, climate impacts on oceans and marine resources intersect with many regions and sectors that are also considered in the NCA.