Title: Fourth National Climate Assessment, Chapter 9: Oceans and Marine Resources

Agency: U.S. Global Change Research Program

Comments Close: January 31st, 2018

Summary Index: 

  1. Purpose
  2. Context: The National Climate Assessment & US Global Change Research Program; Chapter 9 Writing Process; Tips for Chapter Review
  3. Details: Key Messages; Summary of Three Key Messages



Volume II of the Fourth National Climate Assessment “summarizes the impacts of climate change on the United States, now and in the future” (GlobalChange.gov).

Chapter 9, “Oceans and Marine Resources,” reviews the ways in which ocean ecosystems, and the resources they provide, are impacted by climate change. The chapter focuses on three primary factors of ocean change: warming seas, ocean acidification, and deoxygenation. These factors can amplify by interacting with one another as well as other stressors (e.g. nutrient loading). The most acute impacts of climate change are occurring in tropical and polar ecosystems, and are leading to loss of coral reefs and polar sea ice. These ocean transformations are already impacting the US economy, and coastal communities and cultures.




The National Climate Assessment & The Global Change Research Program

The National Climate Assessment is a scientific report synthesized by the US Global Change Research Program.  The Program, established by Presidential Initiative in 1989 and mandated by Congress in 1990, is made up of 13 federal agencies that “conduct or use research on global change and its impacts on society." The purpose of the Program is “to assist the Nation and the world to understand, assess, predict and respond to human-induced and natural processes of global change” (GlobalChange.gov).

Chapter Writing Process

Chapter 9: Oceans & Marine Resources was written by a group of both early-career and senior scientists 'who have experience across the range of marine ecosystems... and with expertise on the main drivers of ecosystem change.' Stakeholder input was provided through a town hall meeting at the Association for the Study of Limnology and Oceanography Annual Meeting, as well as a webinar hosted by the National Oceanic and Atmospheric Administration. 

Tips for Chapter Review

Each chapter is broken down into sections by “Key Messages.” Chapter 9 begins with a Summary Overview and an overview of the 'State of the Ocean' before delving into each key message. Each one- to two-sentence Key Message is followed by a short section that contains a summary of the literature and data that support and expand upon the message. In Chapter 9, this includes the following sections: (1) Project Impacts, (2) Opportunities for Reducing Risk, (3) Emerging Issues / Research Gaps, and (4) Conclusion. 

At the end of each chapter is a final “Traceable Accounts” section, which gives a brief overview of how the chapter was developed. This section then goes on to address the following for each Key Message: (1) describes where evidence for that key message was drawn from, including major projects and particularly critical studies, (2) acknowledges major uncertainties in conclusions and related data, and (3) classifies scientists’ confidence in conclusions.




Chapter 9 Key Messages

  • Ocean Ecosystems
  • Marine Fisheries
  • Extreme Events


Key Message 1: Ocean Ecosystems

'The Nation’s valuable ocean ecosystems are being disrupted by increasing global temperatures through the loss of iconic and highly-valued habitats and changes in species composition and food web structure. Ecosystem disruption will intensify as ocean warming, acidification, deoxygenation, and other aspects of climate change increase. In the absence of significant reductions in carbon emissions, transformative impacts on ocean ecosystems cannot be avoided.'

Cited data and figures include:

  • Projected changes in sea surface temperature (Figure 9.1), pH conditions, and oxygen concentrations
  • Species sensitivity to changing oceans that lead to documented changes in abundance. local extinctions, and range shifts
  • Projected reorganization of marine communities and exposure of organisms to novel stressors
  • Documented coral bleaching and disease outbreaks from ocean warming
  • Documented decline of coral cover on reefs
  • Documented and projected decline of the extent of sea ice

Data sources include:

  • Peer-reviewed scientific studies
  • Recent ecosystem-modeling projects

Uncertainties include:

  • Ecosystem impacts of ocean acidification
  • Impacts of multiple interacting stressors
  • Adaptive capacity of different species
  • Projections that involve future decision-making



Key Message 2: Marine Fisheries

'The Nation’s valuable marine fisheries and fishing communities are at high risk from climate-driven changes in the distribution, timing, and productivity of fishery-related species. Ocean warming, acidification, and deoxygenation are projected to increase changes in fishery-related species, reduce catches in some areas, and challenge effective management of marine fisheries and protected species. Fisheries management that incorporates climate knowledge can help reduce impacts, promote resilience, and increase the value of marine resources in the face of changing ocean conditions.'

Cited data and figures include:

  • Projected percent change in fisheries catch potential between the 2000s and 2050 (Figure 9.2)
  • Model predictions of how climate change will impact 'spatially-explicit abundance, growth, biomass, and catch potential of exploited marine resources,' given strong evidence from ecological theory and experimental studies  'that fluctuations in ocean temperature are associated with changes in the distribution, productivity, and timing of key life-history events of fish and invertebrates'
  • Models of "climate-ready fishery management" that show how 'climate-ready, ecosystem-based fisheries management can help reduce the impacts of some anticipated changes and increase resilience'

Data sources include:

  • Peer-reviewed scientific studies
  • Results from the Dynamic Bioclimatic Envelope Model (DBEM)
  • National and regional efforts 'to characterize community vulnerability to climate change and ocean acidification'

Uncertainties include:

  • Impacts of ocean acidification on wild fish stocks
  • Interactions between fisheries management, future non-climate stressors (i.e. fishing, coastal pollution) and climate change
  • Potential for evolutionary adaptation, and the effects such adaptation might have on the outcomes of DBEM models
  • Predictions of primary productivity, oxygen and pH at regional, coastal scales


Key Message 3: Extreme Events

'Marine ecosystems and the coastal communities that depend on them are at risk of significant impacts from extreme events with combinations of very high temperatures, very low oxygen levels, or very acidified conditions. These unusual events will become more common and more severe in the future, and they expose vulnerabilities that can motivate change including technological innovations to detect, forecast, and mitigate adverse conditions.'

Cited data and figures include: 

  • Documented marine heatwaves affecting the US since 2012 (Figure 9.3)
  • Susceptibility of coastal communities and fisheries to extreme events related to heat, dissolved oxygen, or pH
  • Documented susceptibility of coastal communities and fisheries to extreme events related to heat, dissolved oxygen, or pH
  • Increased frequency of ocean acidification events, and the projected increased in intensity, duration, and frequency of these events
  • Increase in frequency and intensity of hypoxic events produced by increased ocean temperatures and the direct effects of human activities (such as increased nutrient load)

Data sources include:

  • Peer-reviewed scientific studies
  • Documentation of extreme events such as toxic algal blooms, extreme corrosive or low oxygen periods, and abrupt warming. 

Uncertainties include: 

  • How patterns of natural climate cycles will play out in the future under higher atmospheric CO2 concentrations
  • The role of sea ice loss in future weather extremes
  • Regional factors such as 'local nutrient runoff, freshwater input... variability in upwelling strength, cloud cover, and stability of sedimentary deposits'



Are you a scientist at or near the University of Washington? Attend the UW Program on Climate Change's workshop for this chapter's review. More details here



Note that all single quotes ‘’ cite from the Chapter Two draft text; material in double quotes “” may come from any of the sources below.

"Chapter 9: Oceans and Marine Resources." In Fourth National Climate Assessment. US Global Change Research Program. Chapter Lead: Andrew Pershing, Gulf of Maine Research Institute.

"About USGCRP." United States Global Change Research Program. Retrieved from: www.globalchange.gov/about









Contributor: Assistant Professor, Aquatic Ecology