Greenland ice sheet is melting from the bottom up and It is now the largest contributor to global sea level rise, a new study warns.
The researchers observed “unprecedented” rates of melting at the bottom of the ice sheet, caused by massive amounts of meltwater falling from the surface to the base.
As meltwater falls, the energy is converted into heat in a similar way to how hydroelectric power is generated by large dams.
This effect It is by far the largest source of heat under the second largest ice sheet in the world, and it is an international source The team of scientists led by the University of Cambridge found, Which results in tremendously high rates of melting at its base.
Warning: The Greenland ice sheet (pictured) is melting from the bottom up and is now the biggest contributor to global sea level rise, a new study finds
The researchers observed “unprecedented” rates of melting at the bottom of the ice sheet (pictured), caused by massive amounts of meltwater dripping from the surface to the base.
How does global warming affect ice retreat?
Global warming is causing temperatures to rise around the world.
This is especially evident at latitudes near the poles.
Rising temperatures, permafrost, glaciers and ice sheets struggle to stay tactful in the face of warmer climates.
As temperatures rise more than a degree above pre-industrial levels, the ice continues to melt.
For example, melting ice on the Greenland ice sheet leads to the production of “meltwater lakes”, which then contribute to increased melt.
This positive feedback loop is also found on glaciers over mountains.
Many of these have been frozen since the last Ice Age and researchers are seeing a major retreat.
Some animal and plant species are highly dependent on the cold conditions provided by the glaciers and migrate to higher altitudes to find suitable habitat.
This leads to severe pressures on ecosystems as more animals and more species live in an ever-shrinking area.
On top of the environmental stress, the lack of ice on the mountains greatly increases the risks of landslides and volcanic eruptions.
This phenomenon is found in many mountain ranges around the world.
It has also been seen in regions of Antarctica.
The lubricating effect of meltwater has a strong influence on glacier movement and the amount of ice discharged into the ocean, but directly measuring conditions under more than half a mile (one kilometer) of ice to the bottom is challenging, especially in Greenland where glaciers are among the fastest moving In the world.
Experts say this makes it difficult to understand the dynamic behavior of the Greenland ice sheets and to predict future changes
Every summer, thousands of lakes and melt streams form on the surface of the ice sheet as temperatures rise and sunlight increases daily.
But many of these lakes quickly drain to the bottom, falling through large cracks and fractures that form in the ice.
With the continued supply of water from streams and rivers, the connections between the deck and bed often remain open.
Professor Paul Kristofferson of the Scott Polar Research Institute in Cambridge has been studying meltwater lakes, how and why they are draining so quickly, and their impact on the overall behavior of the ice sheet as global temperatures continue to rise.
The current work, which includes researchers from Aberystwyth University, is the culmination of a seven-year study focused on Store Glacier, one of Greenland’s largest ice cap vents.
“When studying the primary melting of ice sheets and glaciers, we look at heat sources such as friction, geothermal energy, and latent heat released as water freezes and heat is lost in the ice above,” Kristofferson said.
But what we haven’t really looked at is the heat from the meltwater discharge itself.
“There is a lot of gravitational energy stored in the water that forms on the surface and when it falls, the energy has to go somewhere.”
To measure melt rates at the base of the ice sheet, the researchers used radio-echo sounding, a technique developed at the British Antarctic Survey and previously used on floating ice sheets in Antarctica.
“We were not sure this technology would also work on a fast-flowing Greenland glacier,” said fellow author Dr Tun Jan Young, who installed the radar system at Store Glacier as part of his PhD thesis at Cambridge.
“Compared to Antarctica, the ice deforms very quickly and there is a lot of meltwater in the summer, which complicates the work.”
The melt rates at the base were found to be as high as those measured at the surface with a weather station.
This is despite the fact that the surface receives heat from the sun while the base does not.
To interpret the results, the Cambridge researchers collaborated with scientists at the University of California Santa Cruz and the Geological Survey of Denmark and Greenland.
Every summer, thousands of lakes and melt streams form on the surface of the ice sheet as temperatures rise and sunlight increases daily.
But many of these lakes drain quickly to the bottom, falling through the cracks and large fractures that form in the ice (pictured)
The researchers estimated that up to 82 million cubic meters of meltwater was carried to the bottom of the Store Glacier per day during the summer of 2014.
They estimated that the energy produced by falling water during periods of maximum melt is comparable to the energy produced by China’s Three Gorges Dam, the world’s largest hydroelectric power plant.
Researchers have found that with a melt area of nearly one million square kilometers at the height of summer, the Greenland ice sheet produces more hydropower than the world’s ten largest hydroelectric plants combined.
“Given what we’re seeing at higher latitudes in terms of climate change, this form of hydropower could easily double or triple, and we still don’t include these numbers even when we estimate the contribution of ice sheet to sea level rise,” Christophersen said.
The researchers compared temperature measurements from sensors installed in a nearby well to check the melt rates recorded by the radar.
At the base, they found that the water has a temperature of 33 degrees Fahrenheit (0.88 degrees Celsius), which is unexpectedly warm for the base of an ice sheet with a melting point of 31 degrees Fahrenheit (-0.40 degrees Celsius).
“The well observations confirmed that meltwater rises when it hits the bed,” Kristofferson said.
The researchers estimated that up to 82 million cubic meters of meltwater was carried to the bottom of the Store Glacier per day during the summer of 2014.
As meltwater falls, the energy is converted into heat in a similar way to how hydroelectric power is generated by large dams (pictured)
The reason is that the primary drainage system is much less efficient than the fractures and channels that carry water through the ice. Low drainage efficiency results in frictional heating within the water itself.
When we extracted this heat source from our calculations, estimates of the theoretical melt rate were two whole orders of magnitude.
“The heat generated by the falling water melts the ice from the bottom up, and the rate of melting we are reporting is completely unprecedented.”
The researchers said their study provides the first concrete evidence for the mechanism of ice mass loss, which has not yet been included in global sea-level rise projections.
While high rates of melt are specific to heat generated in subglacial drainage pathways that carry surface water, the volume of surface water produced in Greenland is huge and growing, almost all of which drains to the bottom.
The study was published in the journal Proceedings of the National Academy of Sciences.
Sea levels could rise by up to 4 feet by 2300
Scientists have warned that global sea levels could rise by 1.2 meters (4 feet) by 2300 even if we meet the 2015 Paris climate goals.
The long-term change will be driven by a melting ice from Greenland to Antarctica that is set to redraw global coastlines.
Sea-level rise threatens cities from Shanghai to London, to lower swaths of Florida or Bangladesh, and to entire countries like the Maldives.
It is critical that we reduce emissions as quickly as possible to avoid an even greater rise, a team of researchers led by Germany said in a new report.
By 2300, the report predicts sea levels will rise by 0.7-1.2 metres, even if nearly 200 countries fully achieve targets under the 2015 Paris Agreement.
Targets set by the agreements include reducing greenhouse gas emissions to net zero in the second half of this century.
She added that ocean levels would rise relentlessly because industrial gases released from trapping heat would linger in the atmosphere, melting more ice.
In addition, water naturally expands when it is heated above four degrees Celsius (39.2 degrees Fahrenheit).
Every five years delay beyond 2020 in peak global emissions means an additional 20 centimeters (8 inches) sea level rise by 2300.
“Sea level is often reported as a really slow process that you can’t do much about…but the next 30 years are really important,” said lead author Dr. Matthias Mengele, from the Potsdam Institute for Climate Impact Research in Potsdam. Germany.
None of the 200 governments that signed the Paris Accords are on track to deliver on their commitments.
