February 13, 2014 at 3:36 am #4848
Sea level data by CU Sea Level Research Group – University of Colorado http://sealevel.colorado.edu/
Sea level and dry land
Several terms are used to describe the changing relationships between sea level and dry land. When the term “relative” is used, it means change relative to a fixed point in the sediment pile. The term “eustatic” refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps.
The term “steric” refers to global changes in sea level due to thermal expansion and salinity variations. The term “isostatic” refers to changes in the level of the land relative to a fixed point in the earth, possibly due to thermal buoyancy or tectonic effects; it implies no change in the volume of water in the oceans. The melting of glaciers at the end of ice ages is one example of eustatic sea level rise. The subsidence of land due to the withdrawal of groundwater is an isostatic cause of relative sea level rise.
Paleoclimatologists can track sea level by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America. Areas like volcanic islands are experiencing relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink.
On other planets that lack a liquid ocean, planetologists can calculate a “mean altitude” by averaging the heights of all points on the surface. This altitude, sometimes referred to as a “sea level”, serves equivalently as a reference for the height of planetary features.
Local and eustatic sea level
Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes.
Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. Changes in ground-based ice volume also affect local and regional sea levels by the readjustment of the geoid and true polar wander. Atmospheric pressure, ocean currents and local ocean temperature changes can affect LMSL as well.
Eustatic change (as opposed to local change) results in an alteration to the global sea levels due to changes in either the volume of water in the world oceans or net changes in the volume of the ocean basins.
Global sea level trend during 1993–2012 Here we investigate the global-mean sea level (GMSL) change during 1993–2012 using Empirical Mode Decomposition, in an attempt to distinguish the trend over this period from the interannual variability. It is found that the GMSL rises with the rate of 3.2 ± 0.4 mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012. This deceleration is mainly due to the slowdown of ocean thermal expansion in the Pacific during the last decade, as a part of the Pacific decadal-scale variability, while the land-ice melting is accelerating the rise of the global ocean mass-equivalent sea level. Recent rapid recovery of the rising GMSL from its dramatic drop during the 2011 La Niña introduced a large uncertainty in the estimation of the sea level trend, but the decelerated rise of the GMSL appears to be intact. http://www.sciencedirect.com/science/article/pii/S0921818113002397
The land-ice contribution to 21st century dynamic sea-level rise .. we ﬁnd that the pattern of DSL change is independent of warming scenario, and appears to scale according to the freshwater input. Consequently, the pattern of ice melt related DSL may be linearly added to other components such as 15 those associated with heat uptake and changes to the hydrological cycle. http://www.ocean-sci-discuss.net/11/123/2014/osd-11-123-2014.pdf
An improved mass budget for the Greenland ice sheet Extensive ice thickness surveys by NASA’s Operation IceBridge enable over a decade of ice discharge measurements at high precision for the majority of Greenland’s marine-terminating outlet glaciers, prompting a reassessment of the temporal and spatial distribution of glacier change. Annual measurements for 178 outlet glaciers reveal that, despite widespread acceleration, only 15 glaciers accounted for 77% of the 739 ± 29 Gt of ice lost due to acceleration since 2000 and four accounted for ~50%. Among the top sources of loss are several glaciers that have received little scientific attention. The relative contribution of ice discharge to total loss decreased from 58% before 2005 to 32% between 2009 and 2012. As such, 84% of the increase in mass loss after 2009 was due to increased surface runoff. These observations support recent model projections that surface mass balance, rather than ice dynamics, will dominate the ice sheet’s contribution to 21st century sea level rise. http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/abstract
Warmer world may wreak havoc with the Atlantic A warming world could slow the circulation of the Atlantic Ocean, potentially triggering African droughts and more rapid sea level rise around Europe. If it happens, it won’t be the first time the Atlantic has been disrupted during a warm period. http://www.newscientist.com/article/dn25093-warmer-world-may-wreak-havoc-with-the-atlantic.html
Expert assessment of sea-level rise by AD 2100 and AD 2300Large uncertainty surrounds projections of global sea-level rise, resulting from uncertainty about future warming and an incomplete understanding of the complex processes and feedback mechanisms that cause sea level to rise. Consequently, existing models produce widely differing predictions of sea-level rise even for the same temperature scenario. Here we present results of a broad survey of 90 experts who were amongst the most active scientific publishers on the topic of sea level in recent years. They provided a probabilistic assessment of sea-level rise by AD 2100 and AD 2300 under two contrasting temperature scenarios. For the low scenario, which limits warming to <2 °C above pre-industrial temperature and has slowly falling temperature after AD 2050, the median ‘likely’ range provided by the experts is 0.4–0.6 m by AD 2100 and 0.6–1.0 m by AD 2300, suggesting a good chance to limit future sea-level rise to <1.0 m if climate mitigation measures are successfully implemented. In contrast, for the high warming scenario (4.5 °C by AD 2100 and 8 °C in AD 2300) the median likely ranges are 0.7–1.2 m by AD 2100 and 2.0–3.0 m by AD 2300, calling into question the future survival of some coastal cities and low-lying island nations. http://www.sciencedirect.com/science/article/pii/S0277379113004381
Australia’s Flooding Rains Briefly Slowed Sea Level Rise http://www.climatecentral.org/news/floods-in-australia-briefly-slowed-sea-level-rise-study-finds-16373
Rising Sea Level May Trigger Groundwater Floods http://www.climatecentral.org/news/rising-sea-level-may-trigger-groundwater-floods-15229
Each degree of global warming might ultimately raise global sea levels by more than 2 meters http://climatestate.com/2013/08/13/each-degree-of-global-warming-might-ultimately-raise-global-sea-levels-by-more-than-2-meters/
The Fingerprints of Sea Level Change http://climatestate.com/2014/02/14/the-fingerprints-of-sea-level-change/
See http://climatestate.com/forums/topic/sea-level-rise-slr/ for associated SLR impacts.
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