Coastal Climate Change

Earth’s climate is now changing faster than at any point in the history of modern civilization, primarily as a result of human activities. Global climate change has already resulted in a wide range of impacts across every region of the United States. Oceans are warming, rising, and becoming more acidic, and heavy precipitation events occur more often leading to increased flooding along the U.S. coastline.

Below are links to reports that provide a general overview of climate change as it affects coastal areas.

The Fifth National Climate Assessment

The Fifth National Climate Assessment is the US Government’s preeminent report on climate change impacts, risks, and responses. It is a congressionally mandated interagency effort that provides the scientific foundation to support informed decision-making across the United States.

  • Overview
    • The effects of human-caused climate change are already far-reaching and worsening across every region of the United States. Rapidly reducing greenhouse gas emissions can limit future warming and associated increases in many risks. Across the country, efforts to adapt to climate change and reduce emissions have expanded since 2018, and US emissions have fallen since peaking in 2007. However, without deeper cuts in global net greenhouse gas emissions and accelerated adaptation efforts, severe climate risks to the United States will continue to grow.
  • Chapter 9: Coastal Effects
    • Climate impacts, including rising sea levels and shifting storm patterns, are transforming coastal landscapes and undermining the resilience of communities and ecosystems. Proactive community-led adaptation strategies, including nature-based solutions and planned relocation, can help communities adapt to both current and future increases in the severity of coastal hazards across the US.
  • Chapter 10: Ocean Ecosystems and Marine Resources
    • Climate change is altering US marine ecosystems in unprecedented ways, leading to shifts in species’ location, productivity, and seasonal timing. This poses risks to fisheries, tourism, recreation, transportation, energy, and other economic sectors—and also undermines critical connections between people and the ocean, especially within Indigenous communities. Swift implementation of equity-focused adaptation and mitigation could help limit future risks.
  • Chapter 22: Southeast
    • The Southeast’s growing population faces increasing threats from climate change, with impacts on human health, ecosystems, economies, infrastructure, and food systems. While there have been notable advancements in adaptation throughout the region, these efforts tend to be concentrated in wealthier coastal and metropolitan areas, leaving rural and other under-resourced communities at risk. Coordinated climate strategies could improve equity, well-being, and economic vitality.
  • Chapter 31: Adaptation
    • Adaptation activities are occurring across the US but have been small in scale, incremental in approach, and lacking in sufficient investment. Transformative approaches will be necessary to adequately address current and future risks. To improve capacity and promote an equitable future, adaptation activities must address the uneven distribution of climate harms and incorporate collaboration with local communities.

Another Year of Record Heat for the Oceans

Changes in ocean heat content (OHC), salinity, and stratification provide critical indicators for changes in Earth’s energy and water cycles. These cycles have been profoundly altered due to the emission of greenhouse gasses and other anthropogenic substances by human activities, driving pervasive changes in Earth’s climate system. In 2022, the world’s oceans, as given by OHC, were again the hottest in the historical record and exceeded the previous 2021 record maximum. According to IAP/CAS data, the 0–2000 m OHC in 2022 exceeded that of 2021 by 10.9 ± 8.3 ZJ (1 Zetta Joules = 1021 Joules); and according to NCEI/NOAA data, by 9.1 ± 8.7 ZJ. Among seven regions, four basins (the North Pacific, North Atlantic, the Mediterranean Sea, and southern oceans) recorded their highest OHC since the 1950s. The salinity-contrast index, a quantification of the “salty gets saltier—fresh gets fresher” pattern, also reached its highest level on record in 2022, implying continued amplification of the global hydrological cycle. Regional OHC and salinity changes in 2022 were dominated by a strong La Niña event. Global upper-ocean stratification continued its increasing trend and was among the top seven in 2022.

Cheng, L., Abraham, J., Trenberth, K.E. et al. Another Year of Record Heat for the Oceans. Adv. Atmos. Sci. 40, 963–974 (2023).

IPCC Synthesis Report of the Sixth Assessment Report
IPCC Sixth Assessment Report: Climate Change 2022: Impacts, Adaptation and Vulnerability

The Working Group II contribution to the IPCC Sixth Assessment Report assesses the impacts of climate change, looking at ecosystems, biodiversity, and human communities at global and regional levels. It also reviews vulnerabilities and the capacities and limits of the natural world and human societies to adapt to climate change.

Cross-Chapter Papers

2022 Global and Regional Sea Level Rise Scenarios for the United States: Technical Report; Sea Level Rise and Coastal Flood Hazard and Tools Interagency Task Force

The Sea Level Rise Technical Report provides the most up-to-date sea level rise projections available for all U.S. states and territories; decision-makers will look to it for information.

This multi-agency effort, representing the first update since 2017, offers projections out to the year 2150 and information to help communities assess potential changes in average tide heights and height-specific threshold frequencies as they strive to adapt to sea level rise.

There were four main takeaways from the report:

  • The Next 30 Years of Sea Level Rise. Sea level along the U.S. coastline is projected to rise, on average, 10 – 12 inches (0.25 – 0.30 meters) in the next 30 years (2020 – 2050), which will be as much as the rise measured over the last 100 years (1920 – 2020). Sea level rise will vary regionally along U.S. coasts because of changes in both land and ocean height.
  • More Damaging Flooding Projected. Sea level rise will create a profound shift in coastal flooding over the next 30 years by causing tide and storm surge heights to increase and reach further inland. By 2050, “moderate” (typically damaging) flooding is expected to occur, on average, more than 10 times as often as it does today, and can be intensified by local factors.
  • Emissions Matter. Current and future emissions matter. About 2 feet (0.6 meters) of sea level rise along the U.S. coastline is increasingly likely between 2020 and 2100 because of emissions to date. Failing to curb future emissions could cause an additional 1.5 – 5 feet (0.5 – 1.5 meters) of rise for a total of 3.5 – 7 feet (1.1 – 2.1 meters) by the end of this century.
  • Continual Tracking. Continuously tracking how and why sea level is changing is an important part of informing plans for adaptation. Our ability to monitor and understand the individual factors that contribute to sea level rise allows us to track sea level changes in a way that has never before been possible (e.g., using satellites to track global ocean levels and ice sheet thickness). Ongoing and expanded monitoring will be critical as sea levels continue to rise.
Climate Change 2021: The Physical Science Basis

The Working Group I contribution to the Sixth Assessment Report is the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science, and combining multiple lines of evidence from paleoclimate, observations, process understanding, and global and regional climate simulations.

  • Summary for Policymakers
    • The Summary for Policymakers (SPM) provides a high-level summary of the understanding of the current state of the climate, including how it is changing and the role of human influence, and the state of knowledge about possible climate futures, climate information relevant to regions and sectors, and limiting human-induced climate change. (39 pages)
  • Chapter 9: Ocean, cryosphere, and sea level change
    • This chapter assesses past and projected changes in the ocean, cryosphere and sea level using paleo-reconstructions, instrumental observations and model simulations. In the following summary, we update and expand the related assessments from the IPCC Fifth Assessment Report (AR5), the Special Report on Global Warming of 1.5oC (SR1.5) and the Special Report on Ocean and Cryosphere in a Changing Climate (SROCC). Major advances in this chapter since the SROCC include the synthesis of extended and new observations, which allows for improved assessment of past change, processes and budgets for the last century, and the use of a hierarchy of models and emulators, which provide improved projections and uncertainty estimates of future change. In addition, the systematic use of model emulators makes our projections of ocean heat content, land-ice loss and sea level rise fully consistent both with each other and with the assessed equilibrium climate sensitivity and projections of global surface air temperature across the entire report.
  • Chapter 11: Weather and climate extreme events in a changing climate
    • This chapter assesses changes in weather and climate extremes on regional and global scales, including observed changes and their attribution, as well as projected changes. The extremes considered include temperature extremes, heavy precipitation and pluvial floods, river floods, droughts, storms (including tropical cyclones), as well as compound events (multivariate and concurrent extremes).
State of the Climate in 2020

This is the 31st issuance of the State of the Climate, published in the Bulletin of the American Meteorological Society since 1996. As a supplement to the Bulletin, its foremost function is to document the status and trajectory of many components of the climate system. However, as a series, the report also documents the status and trajectory of our capacity and commitment to observe the climate system.

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Special Report on the Ocean and Cryosphere in a Changing Climate (2019)

This special report assesses new knowledge since the IPCC 5th Assessment Report and the Special Report on Global Warming of 1.5°C on how the ocean and cryosphere have and are expected to change with ongoing global warming, the risks and opportunities these changes bring to ecosystems and people, and mitigation, adaptation and governance options for reducing future risks. Global mean sea level (GMSL) is rising, with acceleration in recent decades due to increasing rates of ice loss from the Greenland and Antarctic ice sheets (very high confidence), as well as continued glacier mass loss and ocean thermal expansion. Increases in tropical cyclone winds and rainfall, and increases in extreme waves, combined with relative sea level rise, exacerbate extreme sea level events and coastal hazards (high confidence). Extreme wave heights, which contribute to extreme sea level events, coastal erosion and flooding, have increased in the Southern and North Atlantic Oceans by around 1.0 cm yr–1 and 0.8 cm yr–1 over the period 1985–2018 (medium confidence). Sea ice loss in the Arctic has also increased wave heights over the period 1992–2014 (medium confidence). 

State of the Climate in 2019

This is the 30th edition of what is now known as the State of the Climate report. Compared to that 30-year record, this 2019 edition is the richest report in the series, well above climatological averages, and indeed setting records for climate variables tracked and for author participation. This year, 528 authors and editors contributed to the report, together representing 61 countries. As usual, an overview of findings is presented in the Abstract. Chapter 2 features global-scale climate variables; Chapter 3 highlights the global oceans; and Chapter 4 discusses tropical climate phenomena including tropical cyclones. The Arctic and Antarctica respond differently through time and are reported in separate chapters (5 and 6, respectively). Chapter 7 provides a regional perspective authored largely by regional government climate specialists. A list of relevant datasets and their sources for all chapters is provided as an Appendix. Authors, acknowledgments, and references are now listed with each individual chapter.

State of the Climate 2018

This report, produced by the American Meteorological Society, endeavors to bring a comprehensive set of measurements to detail the status of the climate system and our capacity and willingness to observe it. An overview of findings is presented in the Abstract. Chapter 2 features global-scale climate variables; Chapter 3 highlights the global oceans; and Chapter 4 discusses tropical climate phenomena including tropical cyclones. The Arctic and Antarctica respond differently through time and are reported in separate chapters (5 and 6, respectively). Chapter 7 provides a regional perspective authored largely by local government climate specialists. A list of relevant datasets and their sources for all chapters is provided as an Appendix.

Fourth National Climate Assessment Volume II: Impacts, Risks, and Adaptation in the United States (2017)

Volume II of the Fourth National Climate Assessment focuses on the human welfare, societal, and environmental elements of climate change and variability for 10 regions and 18 national topics, with particular attention paid to observed and projected risks, impacts, consideration of risk reduction, and implications under different mitigation pathways. Where possible, NCA4 Vol. II provides examples of actions underway in communities across the United States to reduce the risks associated with climate change, increase resilience, and improve livelihoods.

Climate Science Special Report: Fourth National Climate Assessment (NCA4), Volume I (2014)

The Climate Science Special Report (CSSR) is designed to be an authoritative assessment of the science of climate change, with a focus on the United States, to serve as the foundation for efforts to assess climate-related risks and inform decision-making about responses. This report provides: 1) an updated detailed analysis of the findings of how climate change is affecting weather and climate across the United States; 2) an executive summary and other CSSR materials that provide the basis for the discussion of climate science found in the second volume of the NCA4; and 3) foundational information and projections for climate change, including extremes, to improve “end-to-end” consistency in sectoral, regional, and resilience analyses within the second volume.