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Questions and Answers
What contributes the most to global mean sea level rise in the 20th century?
What contributes the most to global mean sea level rise in the 20th century?
What percentage of global mean sea level rise is explained by thermal expansion, glacier mass loss, and land water storage from 1971-2010?
What percentage of global mean sea level rise is explained by thermal expansion, glacier mass loss, and land water storage from 1971-2010?
What is the likely consequence of sustained global warming beyond a certain threshold?
What is the likely consequence of sustained global warming beyond a certain threshold?
What is the confidence level regarding future global mean sea level rise continuing beyond 2100?
What is the confidence level regarding future global mean sea level rise continuing beyond 2100?
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Which factor is projected to have a high confidence in its effect on sea level rise?
Which factor is projected to have a high confidence in its effect on sea level rise?
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What is the primary method used for monitoring longer-term sea level changes?
What is the primary method used for monitoring longer-term sea level changes?
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Which satellite mission has been instrumental in measuring sea surface since 1992?
Which satellite mission has been instrumental in measuring sea surface since 1992?
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What influences the short-term sea level variability measured by satellites?
What influences the short-term sea level variability measured by satellites?
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Which of the following methods aids scientists in correlating sedimentary cycles globally?
Which of the following methods aids scientists in correlating sedimentary cycles globally?
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During which geological period did the most recent significant glaciation occur?
During which geological period did the most recent significant glaciation occur?
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What evidence shows that sea levels have alternated between high and low stands throughout Earth's history?
What evidence shows that sea levels have alternated between high and low stands throughout Earth's history?
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What term describes the expected future occurrence of ice sheets at high latitudes?
What term describes the expected future occurrence of ice sheets at high latitudes?
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How much did eustatic sea level drop due to the large ice sheets during the Last Glacial Maximum?
How much did eustatic sea level drop due to the large ice sheets during the Last Glacial Maximum?
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What does thermal expansion of seawater primarily lead to?
What does thermal expansion of seawater primarily lead to?
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Which organization is associated with the monitoring of sea levels through tide gauges?
Which organization is associated with the monitoring of sea levels through tide gauges?
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Which factor is considered an eustatic change affecting sea level?
Which factor is considered an eustatic change affecting sea level?
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What is the estimated coverage area of satellite altimeters in terms of latitude?
What is the estimated coverage area of satellite altimeters in terms of latitude?
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What is the approximate rise in sea level from a 1ºC increase in ocean temperature assuming the entire ocean heats uniformly?
What is the approximate rise in sea level from a 1ºC increase in ocean temperature assuming the entire ocean heats uniformly?
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During the assessment period from 1961-2003, what percentage of observed sea-level rise was accounted for by thermal expansion according to the IPCC?
During the assessment period from 1961-2003, what percentage of observed sea-level rise was accounted for by thermal expansion according to the IPCC?
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How does isostatic sea level change primarily occur?
How does isostatic sea level change primarily occur?
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Which of the following best describes steric sea level change?
Which of the following best describes steric sea level change?
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What is the coefficient of thermal expansion of seawater?
What is the coefficient of thermal expansion of seawater?
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What denotes a steric change in sea level, specifically related to temperature?
What denotes a steric change in sea level, specifically related to temperature?
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Which change is NOT associated with contributing to rising sea levels?
Which change is NOT associated with contributing to rising sea levels?
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What is the main cause of melt-water pulses (MWP)?
What is the main cause of melt-water pulses (MWP)?
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Which of the following statements about the last glacial maximum is true?
Which of the following statements about the last glacial maximum is true?
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Which factor contributes most significantly to the fluctuation of sea levels during the Quaternary period?
Which factor contributes most significantly to the fluctuation of sea levels during the Quaternary period?
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What would be the predicted increase in sea level if all polar ice melted?
What would be the predicted increase in sea level if all polar ice melted?
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At what rate is the sea level currently rising?
At what rate is the sea level currently rising?
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What is one of the long-term changes affecting sea level apart from ice melting?
What is one of the long-term changes affecting sea level apart from ice melting?
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Which process is not primarily responsible for changes in the volume of water impacting mean sea level?
Which process is not primarily responsible for changes in the volume of water impacting mean sea level?
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What is the potential impact of post-glacial rebound on mean sea level studies?
What is the potential impact of post-glacial rebound on mean sea level studies?
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The ocean's mean sea level can primarily be affected by which of the following?
The ocean's mean sea level can primarily be affected by which of the following?
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During the last melt-water pulse (MWP1A), what was the rise in sea level?
During the last melt-water pulse (MWP1A), what was the rise in sea level?
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By what year could 300 million people living along the world's coasts be affected by devastating flooding according to the estimates?
By what year could 300 million people living along the world's coasts be affected by devastating flooding according to the estimates?
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Which factor is NOT mentioned as causing local changes in sea level?
Which factor is NOT mentioned as causing local changes in sea level?
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What is the general trend of global average sea level rise per year?
What is the general trend of global average sea level rise per year?
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Which of the following statements about sea level change is accurate?
Which of the following statements about sea level change is accurate?
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What does the term 'inundation' refer to in the context of sea level?
What does the term 'inundation' refer to in the context of sea level?
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Which of these factors is believed to have the least impact on long-term sea level change?
Which of these factors is believed to have the least impact on long-term sea level change?
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What is essential to understand when discussing trends in sea level change?
What is essential to understand when discussing trends in sea level change?
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What type of distance should sea level ideally be measured against?
What type of distance should sea level ideally be measured against?
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Study Notes
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.
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