Εμφάνιση αναρτήσεων με ετικέτα melting of polar ice. Εμφάνιση όλων των αναρτήσεων
Εμφάνιση αναρτήσεων με ετικέτα melting of polar ice. Εμφάνιση όλων των αναρτήσεων

Τετάρτη, 14 Ιανουαρίου 2015

Sea level rise quickens more than thought in threat to coasts

Sea level rise in the past two decades has accelerated faster than previously thought in a sign of climate change threatening coasts from Florida to Bangladesh, a study said today.
The report, reassessing records from more than 600 tidal gauges, found that readings from 1901-90 had over-estimated the rise in sea levels. Based on revised figures for those years, the acceleration since then was greater than so far assumed.

The report said the earlier readings were incomplete or skewed by local factors such as subsidence.

The new analysis "suggests that the acceleration in the past two decades is 25 percent higher than previously thought," Carling Hay, a Canadian scientist at Harvard University and lead author of the study in the journal Nature, told Reuters.

The study said sea level rise, caused by factors including a thaw of glaciers, averaged about 1.2 millimetres (0.05 inch) a year from 1901-90 - less than past estimates - and leapt to 3 mm a year in the past two decades, apparently linked to a quickening thaw of ice.

Last year, the UN's Intergovernmental Panel on Climate Change (IPCC) estimated the 1901-90 rate at 1.5 mm a year, meaning less of a leap to the recent rate around 3 mm.


The Harvard-led study said the new findings might affect projections of the future pace of sea level rise, especially those based on historical trends.

John Church, a top IPCC author at the Commonwealth Scientific and Industrial Research Organisation in Australia, told Reuters he did not expect any impact on the IPCC's core sea level projections, which are not based on past trends.

IPCC scenarios, which range from a sea level rise of 28 to 98 cms this century, are based on the processes driving sea level change, for instance how ice in Greenland reacts to rising temperatures or the expansion of water as it warms, he said.

Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research and a world expert in past sea levels, said further analysis was needed to pin down 20th century sea level rise.

The new findings confirm that "sea level is rising and ... the rise has accelerated, with the most recent rates being the highest on record," he told Reuters.

Sea level rise is gnawing away at shores from Miami to Shanghai. In cities such as Jakarta, the rise is aggravated by big local subsidence.
  [buenosairesherald.com]
14/1/15
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Δευτέρα, 15 Σεπτεμβρίου 2014

Glaciers in northern Antarctic Peninsula melting faster than ever despite increased snowfall

An international team of researchers, led by Dr Bethan Davies, from Royal Holloway, University of London, has discovered that small glaciers that end on land around the Antarctic Peninsula are highly vulnerable to slight changes in air temperature and may be at risk of disappearing within 200 years.

Temperatures are currently rising rapidly in the Antarctic Peninsula. Because warmer air holds more moisture, the amount of snowfall has also increased. Some researchers have suggested that this may offset the melting of the glaciers, however this study found that just a small rise in air temperature increased melting so much that even large amounts of extra snowfall could not prevent glacier recession.


"These small glaciers around the edge of the Antarctic Peninsula are likely to contribute most to rising sea levels over the coming decades, because they can respond quickly to climate change," said Dr Davies, from the Department of Geography at Royal Holloway. "This study is the first to show how glaciers in this vulnerable region are likely to respond to climate change in future. Our findings demonstrate that the melting will increase greatly even with a slight rise in temperature, offsetting any benefits from increased snowfall."

The researchers carried out extensive fieldwork on James Ross Island, northern Antarctic Peninsula, to map and analyse the changes to a glacier, which is currently 4km long, over the past 10,000 years. They used a combination of glacier and climate modelling, glacial geology and ice-core data.

Dr Davies added: "Geological evidence from previous studies suggests that the glacier grew by 10km within the last 5,000 years, before shrinking back to its current position. It was argued that this occurred during a warmer but wetter period, suggesting that increased precipitation in the future would offset the melting of the glaciers. However, our study shows that this growth occurred during the colder 'Little Ice Age', reaching its largest size just 300 years ago."

Researcher Dr Nicholas Golledge, from Victoria University of Wellington, in New Zealand, said: "This glacier, though small, is typical of many of the small glaciers that end on land around the Antarctic Peninsula. This research is important, because it helps reduce some of the uncertainties about how these glaciers will react to changing temperature and precipitation over the next two centuries."

Professor Neil Glasser, from Aberystwyth University, added: "We found that this glacier remained roughly the same size for thousands of years until it started to grow again 1,500 years ago. However, it is now melting faster than anything seen before, and over the next 200 years will become far smaller than at any point over the last 10,000 years. This unprecedented glacier recession, in response to climate change, will result in significant contributions to sea level rise from this and similar Antarctic Peninsula mountain glaciers and ice caps."

http://www.sciencedaily.com/releases/2014/09/140914211024.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily+%28Latest+Science+News+--+ScienceDaily%29
14/9/14
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Παρασκευή, 9 Νοεμβρίου 2012

Enhanced melting of Northern Greenland in a warm climate

Simulated ice thickness for the Greenland ice sheet for the last interglacial period (~126 thousand years before present). This was the most recent period with relatively warm temperatures at high northern latitudes, not unlike what is expected for the 21st century from projections of global warming. Circles show locations with ice core data.
 (Credit: Image courtesy of University of Bergen)

ScienceDaily (Nov. 9, 2012) — In a new study from the Bjerknes Centre for Climate Research, scientists show how the northern part of the Greenland ice sheet might be very vulnerable to a warming climate
The study is based on simulations with a state of the art global climate model and a dynamic ice sheet model of the last interglacial warm period. This period (~126 thousand years before present) is the most recent in Earth's history with temperatures warmer than present in the Arctic region, and has frequently been used as an analogue for a future greenhouse climate. During this period we know that the Greenland ice sheet was significantly reduced in size compared to today.


The model simulations show an extreme retreat of the northern part of the Greenland ice cap in response to the warm interglacial climate, a climate not unlike what we expect on Greenland in the very near future. This result is surprising, as temperatures on the north part of Greenland are colder than in the south. However, increased precipitation compensates for much of the increased melting of the southern part of the ice sheet in a warmer climate.
Today, most scientists expect that the southern part of the Greenland ice sheet is most vulnerable to a changing climate. In particular, there are several studies monitoring ice streams and fjord temperatures along the coast of southern Greenland. However, the new results indicate that the northern part of Greenland, at the fringe of the Arctic Ocean, should be particularly closely. In this area part of the ice sheet is grounded below sea level, and can respond rapidly once it starts receding.
If the Greenland ice sheet were to melt completely, it would result in an increase in mean global sea level by about 7 meters. However, the sea level impact of the observed recent accelerated melt of the ice sheet, as well as future projections of melt from the ice sheet, are not implemented by the current generation of climate models included in the IPCC effort.


Enhanced melting of Northern Greenland in a warm climate
9/11/12

Τετάρτη, 3 Οκτωβρίου 2012

New satellite data reveals sea-level rise

The city of Venice is investing billions in a new flood defence system to protect against sea level rises

(CNN) -- Sea-levels are rising unevenly around the world, with Pacific countries in particular suffering significant increases over the past two decades, according to accurate new satellite data.
On average, global sea-levels have been rising at about three millimeters (mm) a year, however, this masks large differences between regions of the world.

While some regions have seen sea-level rises of 12 mm a year, others have actually seen decreases of about 12 mm a year.
The results are based on radar readings from the European Space Agency (ESA) over an 18-year period from October 1992 to March 2010.
ESA used its satellites to send radar pulses to the sea surface below, recording the time delay in its return and creating a precise measurement of their height above the surface.
Scientists say sea-level rises are the result of the expansion of water due to rising temperatures, melting of glaciers and the melting of polar ice sheets.
Annual mean global sea-level changes 1992-2010 (ESA)Annual mean global sea-level changes 1992-2010 (ESA)
 
The worst hit regions over the past two decades, according to the ESA data, have been the Pacific countries of Indonesia, Papua New Guinea, Philippines and vulnerable Pacific islands like the Solomon Islands.
The Philippines for one is already frequently subjected to flooding and landslides caused by heavy rain, with seasonal monsoon rains in August killing at least 11 people.
Scientists suggest regions that have seen high sea level rises over the past 20 years will not necessarily continue to see higher than average sea-level rises in the future.
"We suspect that the bigger the differences get, the more they will tend to level out in the future," says Robert Meisner, a spokesperson for ESA.
However, a recent study of coastal cities still predicted the Philippines' capital Manila would see its vulnerability to flooding double by the end of the century, due to sea-level rises.
In some regions of the world, the increasingly accurate sea level data is being used by planners to mitigate against the risk of flooding.
In Venice, where the sea-level data was released, engineers are constructing a new set of tidal barriers to protect the historic city.
The city, which attracts millions of tourists every year, is seeing sea-level rises of around 2 mm per year, together with slow, mostly natural, subsidence of about another 2 mm every year.
The new $7.9 billion-barrier system will see giant barriers placed on the sea floor around Venice. When the water levels rise, air will be pumped into the barriers raising them up to block the tidal flow and protect the city from flooding.
The system is due to be completed in 2014 and is expected to be able to protect the city for the next 20 years.
http://edition.cnn.com/2012/10/02/tech/satellites-sea-level-rise/index.html
3/10/12

Οι νεκροί Έλληνες στα μακεδονικά χώματα σάς κοιτούν με οργή

«Παριστάνετε τα "καλά παιδιά" ελπίζοντας στη στήριξη του διεθνή παράγοντα για να παραμείνετε στην εξουσία», ήταν η κατηγορία πο...