Saturday, August 29, 2015

New NASA videos show stark ice loss from Earth's ice sheets

See the link below for videos of changes over time.

Aug. 27, 2015

The US space agency, NASA, yesterday released brand new images showing the pace of ice loss from Earth's two vast ice sheets, Greenland and Antarctica.

The amount of ice lost from the frozen expanses at the very north and south of the planet is accelerating, say the scientists, and together have helped raise global sea level by more than 7cm since 1992.


Changing ocean currents and temperatures are also melting the Greenland ice sheet from the bottom up, scientists say. A new three-year NASA project called Oceans Melting Greenland (OMG ) aims to get a better handle on how the rate of ice loss compares to surface melting.


As ice on land melts, it raises global sea levels. On top of the contribution from melting ice sheets and glaciers, sea water expands as it gets warmer, raising sea levels further still.

NASA scientists have been measuring the height of the surface of the ocean in detail since 1992, first with the Topex/Poseidon satellite and later with its successors, Jason-1 and -2.

Together with the GRACE satellites and the ARGO network of more than 3,000 ocean sensors, scientists now have a good idea of how sea levels are changing.

Globally, sea level has risen by about 19cm since the start of the 20th century, 7.4cm in the last 20 years alone. About a third of that is from warming water, the rest from melting land ice, say the NASA scientists.

But sea level rise doesn't happen at the same speed everywhere. A third new video from NASA below shows how sea level has changed in different parts of the world since 1992. Red is where sea level has risen, blue is where it has fallen.


Differences in sea level rise from one place to another are largely down to ocean currents and natural cycles such El NiƱo and the Pacific Decadal Oscillation, explains Josh Willis, oceanographer at NASA's Jet Propulsion Laboratory and chief scientist behind the coming Jason-3 satellite mission.

But that looks set to change, he says. Scientists predict meltwater from ice sheets will overtake natural cycles to become the most significant contributor to overall sea level change.


So, how much more can we expect sea levels to rise?

Steve Nerem, head of NASA's sea level team, says what we've seen so far from the ice sheets is just the beginning. He says:

"Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it's pretty certain we are locked into at least 3 feet [91cm] of sea level rise and probably more."

The question is whether it will happen over the course of this century or longer, says Nerem.

This is at the upper end of the range of 52-98cm by 2100 put forward in the latest report from the Intergovernmental Panel on Climate Change (IPCC) in 2013, assuming emissions stay very high (RCP8.5). But if the ice sheets collapse altogether, we can expect a lot more than that, says Tom Wagner, scientist at NASA Headquarters in Washington. He says:

"We've seen from the paleoclimate record that sea level rise of as much as 10 feet [3m] in a century or two is possible, if the ice sheets fall apart rapidly."


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