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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• What is the difference between absolute sea level change and relative sea level change?

  Absolute sea level change refers to changes in the height of the ocean's surface relative to the center of the Earth, while relative sea level change is the change in sea level experienced at a specific location, accounting for both the absolute change in the ocean's surface and the vertical movement of the land.

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

  Uncertainty in sea level rise projections from the IPCC AR6 refers to the range of possible future outcomes due to various factors that affect the precision and reliability of predictions. It reflects the complexity of the climate system and the limitations of current scientific understanding and modeling capabilities.

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• What are Shared Socioeconomic Pathways, or SSPs?

  Shared Socioeconomic Pathways (SSPs) are scenarios used in climate research to explore how global society, demographics, and economics might evolve over the 21st century, affecting greenhouse gas emissions and climate change.

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• What is the IPCC Assessment Report Process?

  The Intergovernmental Panel on Climate Change (IPCC) Assessment Report (AR) process involves producing comprehensive evaluations of the current state of climate science, assessing knowledge on climate change, its impacts, and strategies for mitigation and adaptation. 

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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, educators, coastal residents, local and regional decision-makers, government employees, and community planners and resilience staff.

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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. 

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