Trends in global average absolute sea level, 1870–2008. Changes in sea level since the end of the last glacial episode. Current sea level rise is about 3 mm/year worldwide. Between 1870 and 2004, global average sea levels rose 195 mm (7.7 in), 1.46 mm (0.057 in) per year. From 1950 to 2009, measurements show an average annual rise in sea level of 1.7 ± 0.3 mm per year, with satellite data showing a rise of 3.3 ± 0.4 mm per year from 1993 to 2009, a faster rate of increase than previously estimated. It is unclear whether the increased rate reflects an increase in the underlying long-term trend. Two main factors contribute to observed sea level rise. The first is thermal expansion: as ocean water warms, it expands. The second is from the melting of major stores of land ice like glaciers and ice sheets. On the timescale of centuries to millennia, the melting of ice sheets could result in even higher sea level rise. Overview of sea-level change Projections
Shutdown of thermohaline circulationA summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents A shutdown or slowdown of the thermohaline circulation is a postulated effect of global warming. Thermohaline circulation and fresh water The red end of the spectrum indicates slowing in this presentation of the trend of velocities derived from NASA Pathfinder altimeter data from May 1992 to June 2002. Some even fear that global warming may be able to trigger the type of abrupt massive temperature shifts which occurred during the last glacial period: a series of Dansgaard-Oeschger events – rapid climate fluctuations – may be attributed to freshwater forcing at high latitude interrupting the THC. Studies of the Florida Current suggest that the Gulf Stream weakens with cooling, being weakest (by ~10%) during the Little Ice Age. Measurements in 2004, 2005, 2008 and 2010 Bryden measurements reported late 2005 See also
Adam Was BlackSea LevelThis marker indicating sea level is situated between Jerusalem and the Dead Sea, Israel. Sea level is generally used to refer to mean sea level (MSL), an average level for the surface of one or more of Earth's oceans from which heights such as elevations may be measured. MSL is a type of vertical datum – a standardised geodetic reference point – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured in order to calibrate altitude and, consequently, aircraft flight levels. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. The term above sea level generally refers actually to above mean sea level (AMSL). §Measurement Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 200 millimetres (7.9 in) during the 20th century (2 mm/year). §Sea level and dry land
Change and Sea Level RiseMelting of Glaciers and Ice Sheets One of the most pronounced effects of climate change has been melting of masses of ice around the world. Glaciers and ice sheets are large, slow-moving assemblages of ice that cover about 10% of the world’s land area and exist on every continent except Australia. They are the world’s largest reservoir of fresh water, holding approximately 75% (1). Over the past century, most of the world’s mountain glaciers and the ice sheets in both Greenland and Antarctica have lost mass. One of the best-documented examples of glacial retreat has been on Mount Kilimanjaro in Africa. Image from global-greenhouse-warming.com When researching glacial melting, scientists must consider not only how much ice is being lost, but also how quickly. Image from UNEP In Antarctica, recent estimates show a sharp contrast between what is occurring in the East and West Antarctic Ice Sheets. Impacts The melting back of the glaciers and ice sheets has two major impacts. Sea Level Rise
IPCC - Intergovernmental Panel on Climate ChangeHebrew LanguageSOTC: Sea IceSea ice is frozen seawater that floats on the ocean surface. Blanketing millions of square kilometers, sea ice forms and melts with the polar seasons, affecting both human activity and biological habitat. In the Arctic, some sea ice persists year after year, whereas almost all Southern Ocean or Antarctic sea ice is "seasonal ice," meaning it melts away and reforms annually. While both Arctic and Antarctic ice are of vital importance to the marine mammals and birds for which they are habitats, sea ice in the Arctic appears to play a more crucial role in regulating climate. Because they are composed of ice originating from glaciers, icebergs and ice shelves are not considered sea ice. Most of the icebergs infesting North Atlantic shipping lanes originate from Greenland glaciers. Sea ice regulates exchanges of heat, moisture and salinity in the polar oceans. The seasonal sea ice cycle affects both human activities and biological habitats. Monitoring sea ice Decline in Arctic sea ice extent
Sea Levels Rising Fast on U.S. East CoastCharles Q. Choi (Also see "New York, Boston 'Directly in Path' of Sea Level Rise." ) Sea levels worldwide are expected to rise as global warming melts ice and causes water to expand. Now it seems scientists have pinpointed just such a variance. Analyzing tide-level data from much of North America, U.S. Global sea level rise averaged about 0.6 to 1 millimeter annually over the same period. "If you talk with residents of this hot spot area in their 70s or 80s who've lived there all their lives, they'll tell you water is coming higher now in winter storms than it ever did before," said study co-author Peter Howd , an oceanographer contracted with the USGS. "We're now finally getting to the point where we can measure their observations with our highfalutin scientific instruments." (Sea sea level rise pictures .) For residents of New York and cities up and down the eastern seaboard, those numbers should become a lot more than ink on paper. But it's not just cities that are expected to suffer.
EvidenceThe Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. Scientific evidence for warming of the climate system is unequivocal. The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.1 Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. The evidence for rapid climate change is compelling: Sea level rise Global temperature rise Warming oceans Glacial retreat