Resources

Terminology

• What is the difference between "climate prediction" and "climate projection"?

  A climate projection estimates future climate conditions based on various scenarios of greenhouse gas emissions and human activities, providing a range of potential outcomes. In contrast, a climate prediction uses current climate data and models to forecast specific future conditions over a shorter timescale, similar to a weather forecast but for longer periods.

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• What is the difference between a "sea level projection" and a "sea level scenario"?

  A "sea level projection" is a detailed estimate of how much sea levels might rise based on different levels of greenhouse gas emissions and other factors. A "sea level scenario" simplifies these projections into a few possible futures to help policymakers make decisions about coastal development and conservation.

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• What is meant by an "ice sheet fingerprint"?

  Ice sheet fingerprints are called so because they create unique, location-specific patterns of sea level change around the world, much like a fingerprint uniquely identifies an individual. The fingerprints arise because of changes that happen to the gravitation, rotation and deformation of Earth when ice melts.

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Impacts and Causes of Sea Level Rise

• What are the connections between emissions, temperature change, and sea level rise?

  There is strong evidence in the geologic record that global carbon dioxide levels, temperature levels, and sea levels have changed together through time. Human activities, especially emissions of greenhouse gasses, are the dominant cause of increasing global temperatures since the industrial revolution.

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• What causes sea level rise?

  The two major causes of global mean sea level rise are the expansion of ocean water as it warms (thermal expansion) and the added water from land-based ice (e.g., mountain glaciers and ice sheets) as it melts. Both of these processes are driven by increased global temperatures that are associated with greenhouse gas emissions from human activities. At a local level, any vertical land motion that may be occurring — from either natural or anthropogenic factors — can cause changes in ‘relative sea level.’

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• What are the impacts of sea level rise?

  Tens of millions of people in the U.S. and hundreds of millions globally live in areas that are at risk of coastal flooding. Sea level rise does not act alone — rising sea levels, along with sinking lands, will combine with other coastal flood factors like storm surge, wave effects, river flows, and heavy rains to significantly increase the exposure of coastal communities, ecosystems, and economies. Sea level rise threatens infrastructure necessary for local jobs, regional industries, and public safety, such as roads, subways, drinking water supplies, power plants, oil and gas wells, and sewage treatment systems.

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• Why isn’t the rate of sea level rise the same everywhere?

  The global sea level is the average ocean height across the entire planet. It gives an overall picture of how sea levels are changing. Local, or relative, sea level is the height of the ocean compared to the land next to it. The local sea level depends on many factors. Changes in land height, ocean currents, and other natural factors all play a role. When factored in, sea level rise locally can differ from the global rise by 100% or more.

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• How much has sea level risen in the past 100 years?

  Global mean sea level, or the average height of the ocean surface, has risen 6 - 8 inches (15 - 20 centimeters) since 1920. The rate of this sea level rise is increasing...

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• What's the difference between melting sea ice and melting land ice on sea levels?

  Melting sea ice doesn't raise sea levels because it's already floating in the ocean, like ice in a glass of water. However, melting land ice, such as ice in the ice sheets, adds extra water to the ocean, causing sea levels to rise.

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Sea Level Scenarios

• What is the difference between "sea level rise" and "sea level change"?

  Sea Level Change is a broader term that includes both increases and decreases in sea level, affected by various factors. Sea Level Rise is a narrower term, specifically referring to the long-term increase in sea levels due to global warming and climate change.

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• How were the sea level scenarios in the 2022 Technical Report created?

  The 2022 Interagency Technical Report created sea level scenarios by using IPCC AR6 projections to define a range of possible sea level rises from 1 ft to 6.6 ft by 2100. They generated thousands of samples for different emissions pathways, filtered these through set targets, and constructed five time-varying Sea Level Scenarios to guide policy and planning decisions.

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• What does it mean to have “uncertainty” in sea level rise scenarios?

  When considering future sea level changes, there are two main types of uncertainty: process uncertainty, which relates to how well we understand and model the physical processes driving sea level change, and emissions uncertainty, which depends on future human behavior and emissions. Process uncertainty is reflected in the range of values for each scenario, while emissions uncertainty is captured in the range between different scenarios, such as the Low, Intermediate, and High sea level rise scenarios. Additionally, there is ongoing scientific debate about the potential for rapid ice sheet melt, which, though uncertain, could significantly impact the highest sea level rise scenarios.

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2022 Interagency Technical Report

• How are the sea level rise scenarios in the 2022 report different from the 2017 report?

  The 2022 technical report presents five possible global sea level rise scenarios by 2100, ranging from Low (1 foot) to High (6.6 feet), similar to the 2017 report but excluding the Extreme scenario. The projections for 2100 remain unchanged, but updated modeling of ice sheet behavior results in less acceleration in higher scenarios until about 2050, followed by greater acceleration toward the century's end. Consequently, the near-term range of sea level rise is narrower, while the likely range for each scenario is broader compared to the 2017 report.

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• What is included in the 2022 technical report?

  The 2022 Interagency Technical Report uses IPCC AR6 projections to develop sea level rise scenarios tailored for practical use in the United States, providing detailed and localized information for policy-makers, planners, and stakeholders. It includes updated global and regional sea level scenarios to 2150, near-term observation-based trajectories to 2050, and a national set of extreme water level probabilities illustrating changes in high tide flooding frequency by 2050. This report bridges the gap between global scientific assessments and local implementation needs.

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• What are observation-based extrapolations in the 2022 technical report and what do they tell us?

  Observation-based extrapolations, or sea level rise trajectories, estimate relative sea level rise to 2050 by analyzing regional tide gauge data and satellite altimetry, filtering out natural variability effects. The 2022 technical report provides these extrapolations globally and for eight U.S. coastal regions, offering additional evidence and confidence in near-term sea level rise projections. These extrapolations closely align with model-based projections, reinforcing the expected acceleration in sea level rise due to continued global warming

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• What are extreme water levels as used in the report?

  The 2022 Technical Report define extreme water levels as those experienced during various flooding events, ranging from frequent minor floods to rare major floods with a 1% annual chance of occurring. These levels are assessed using NOAA’s flood severity categories and are based on measurements from NOAA tide gauges, reflecting still water levels without wave influences. Extreme water level probabilities are determined through regional frequency analysis of historical tide gauge data, offering a broader and more accurate assessment of flood risk compared to single-gauge data or FEMA estimates, especially for more frequent flooding events.

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• What does it mean when the 2022 Interagency Technical Report says there will be a “flood regime shift” by 2050?

  The 2022 technical report provides information on extreme water levels, ranging from rare to common flooding events, to assess current and future flood exposure considering sea level rise. By 2050, there is expected to be a "flood regime shift," where the frequency of moderate high tide flooding will exceed today's frequency of minor flooding due to rising sea levels. This means that tides and storm surges currently causing minor floods will lead to more severe flooding events, impacting infrastructure and requiring emergency responses more frequently.

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Questions About This Site

• Who is the intended audience for this site?

  This site aims to provide scientifically accurate information on sea level change in an accessible and usable format for journalists, congressional members and staff, K-12 educators, coastal residents, local and regional decision-makers, government employees, and community planners and resilience staff.

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• How does the information on SeaLevel.gov differ from what is in the 2022 technical report?

  The data and methodologies used come directly from the 2022 technical report, but the observed data has been updated to the present.

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• What is included on this site?

  This site provides authoritative, science-based information on sea level change from participating agencies, covering topics like causes, regional differences, measurement methods, projections, and impacts on communities. It features a data explorer with interactive charts, graphs, and audio explainers, and offers downloadable summaries and key messages. The site also includes access to the 2022 Technical Report, Companion Application Guide, and other relevant resources.

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• Why was this site created?

  This site was created to make research on sea level change accessible and usable for the public, without having to navigate numerous sources of information that may or may not be trustworthy, applicable to their use case, or understandable without an advanced science education.

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• This site provides state summaries of the scenarios, high tide flooding. How applicable is the state-level summary data to my town? How do the state summaries compare to the regions that the states are in?

  If your town does not have a tide gauge located nearby, users may choose to look at state-level or region-level information to find out more about what they can expect sea level rise to look like in their area. While the region-level summaries were provided in the 2022 technical report, the state summaries are new to this site. The state-level summary information has been compiled using the same vetted and tested methodologies used in the 2022 technical report to show information that is representative of what each state or territory can expect on average in terms of sea level change.

  In the 2022 technical report, differences across the U.S. coastlines were highlighted by dividing the coast into 10 different regions and providing summary statistics for each of these regions. While useful for looking at high-level differences, in some cases, the applicability of these regional averages to smaller areas was unclear. By further localizing the scenarios and information in the technical report to the state-level, the targeted audiences of this site can have access to more relevant information to understand the changes happening where they are without altering the key messages and science in the 2022 report. Based on how the regions were created and defined in the 2022 technical report, the state-level summaries do not diverge significantly from the summaries of the regions that they are in.

  More local factors - those at more specific locations than state-level - like coastal development, soil and groundwater, coastal armoring, storms, precipitation, and riverine factors can highly influence what coastal inundation and flooding look like locally. The information on this site is a starting point for users to understand past and future changes in sea level, but ithowever should not be a substitute for or supersede localized expertise in topics like engineering, floodplain management, or stormwater management.