Is sea level rising?
Global mean sea level has been rising at an average rate of 1 to 2 mm/year over the past 100 years, which is significantly larger than the rate averaged over the last several thousand years. Projected increase from 1990-2100 is anywhere from 0.09-0.88 meters, depending on which greenhouse gas scenario is used and many physical uncertainties in contributions to sea-level rise from a variety of frozen and unfrozen water sources.
Global mean sea level has been rising at an average rate of 1.7 mm/year (plus or minus 0.5mm) over the past 100 years, which is significantly larger than the rate averaged over the last several thousand years. Depending on which greenhouse gas increase scenario is used (high or low) projected sea-level rise is projected to be anywhere from 0.18 (low greenhouse gas increase) to 0.59 meters for the highest greenhouse gas increase scenario. However, this increase is due mainly to thermal expansion and contributions from melting alpine glaciers, and does not include any potential contributions from melting ice sheets in Greenland or Antarctica. Larger increases cannot be excluded but our current understanding of ice sheet dynamics renders uncertainties too large to be able to assess the likelihood of large-scale melting of these ice sheets.
According to the 2007 Intergovernmental Panel on Climate Change’s Fourth Assessment Report (IPCC AR4), there is strong evidence that global sea level rose gradually in the 20th century and is currently rising at an increased rate. After little change up to 1900, the average rate of global average sea level rise for the 20th century was 1.7 ± 0.5 millimeters per year. The IPCC predicts a conservative rise in the global average sea level between 0.18 and 0.59 meters (between 0.6 and 2 feet) in the next century. The range depends on the degree of warming, which in turn depends on choices made regarding energy choices, economic development and consequently greenhouse gas emissions. This estimate is conservative, as the models do not include all the non-linear processes which could accelerate the rate at which ice sheets melt, such as the impact of warming ocean temperatures below and around ice shelves (that buttress land-based ice sheets) or the acceleration of ice sheet movement due to m
…there is strong evidence that global sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is projected to rise at an even greater rate in this century. The two major causes of global sea level rise are thermal expansion of the oceans (water expands as it warms) and the loss of land-based ice due to increased melting… Yes, there is strong evidence that global sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is projected to rise at an even greater rate in this century. The two major causes of global sea level rise are thermal expansion of the oceans (water expands as it warms) and the loss of land-based ice due to increased melting. Global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (approximately 21,000 years ago)
