Untitled Quiz

Impacts of Climate Change: Sea Level

• Sea level is rising globally, at a rate of a few millimeters per year.
• Sea level rise is not uniform; some areas experience drops.
• When assessing trends, consider the timescales involved. Rapid acceleration is hard to quantify precisely which impacts estimates.
• Sea level is typically measured relative to land but should be measured relative to the Earth's geoid (mean gravitational distance from the Earth's center).
• Sea level change can be due to various factors over different periods and areas - local changes (mostly tides, atmospheric pressure, ocean circulation, and land changes) and global changes (density of seawater changes, total ocean mass changes, ocean basin volume changes).
• A 1°C rise in ocean temperatures (assuming heating of the entire ocean extent) leads to an 84 cm rise in sea level (based on the thermal expansion rate).
• Key changes to sea level are related to density, mass, and volume of water. Eustatic and isostatic changes through time.
• Thermal expansion of water and melting ice cause global sea level rise.
• Steric changes (e.g., thermal expansion) and eustatic changes (e.g., ice melt) contribute to sea level changes.
• Isostatic changes (e.g., land uplift or sinking) are also important in local relative sea level changes.
• Climate change is creating higher sea levels; current levels are unprecedented as the rate of rise is far greater than in past millennia.
• The IPCC Fourth Assessment Report noted that thermal expansion of water accounted for about one-quarter and melting land ice for about half of observed sea level rise (1961-2003). This balance shifted; from 1993-2008 land ice contributed 68% while thermal expansion 35%.
• Measurement methods include in-situ tide gauges (e.g., University of Hawaii Sea Level Center) and remote satellite altimetry.
• Satellites (TOPE/Poseidon, follow-on missions) provide global sea surface and geoid measurements from 1992 to the present.
• Satellites measure shorter-term variability while tide gauges capture longer-term patterns with some exceeding 100 years.
• Studies have shown that sea level rise can vary over different time frames (i.e. years, decades, centuries and even longer).
• The rate of sea level rise is accelerating.
• 300 million people living along coastlines risk devastating flooding by 2050; this estimate is three times higher than previous figures. By 2100, this figure could double to 630 million if greenhouse emissions continue to increase.
• Sea level is rising significantly, due to global warming, which will continue beyond 2100, with effects lasting centuries.
• The future rate of rise in sea levels depends on greenhouse gas emissions.
• Thermal expansion and glacier melt are the main contributors to recent sea level rise but other factors (e.g. land water storage) also contribute.
• Future sea-level rise scenarios based on greenhouse emission pathways (e.g. RCP 8.5), show increasingly higher rising levels.
• The historical data indicate that the current sea level rise is unprecedented.
• Sea levels have previously exceeded 5 m above present levels of warming exceeded by 2° Celsius.
• The recent rate of rise in sea level is significantly greater than in past millennia.
• Processes that further complicate studies, include post-glacial rebound (ice and sediment loading) and GPS vertical velocity studies.
• Ocean thermal expansion and glacier melting have driven the 20th-century rise in sea levels. Projections reveal strong confidence in thermal expansion and Greenland surface mass balance, but a lower degree of confidence around glacier loss and Antarctic surface mass balance.
• The combined factors of thermal expansion, glacier mass loss, and land water storage estimates account for >65% of global sea level rise between 1901-1990 and >90% between 1971-2010 and 1993-2010.
• Sustained global warming above specific thresholds will likely cause near complete Greenland ice-sheet loss, potentially furthering sea level rise by as much as 7m within millennia.
• Regional variations are highly likely during the 21st century as significant deviations from local and regionally averaged values are expected.

Key Concepts

• Sea level is constantly changing and often unpredictable.
• Various factors (e.g., thermal expansion, ice melt, land changes, etc.) influence sea level.
• Time ranges matter when studying sea level trends.
• Quantifying changes in sea level rise is complex; many variables contribute to its evolution.

Implications of Sea Level Rise

• Rising sea levels create significant coast erosion, and flooding threats which further endanger coastal regions.