Scientists warn of perilous climate shift within decades, not centuries – ‘We are in a position of potentially causing irreparable harm to our children, grandchildren, and future generations’Posted by Jim at Friday, March 25, 2016
By Brian Mastroianni
23 March 2016
(CBS News) – A sobering new report on the impact of climate change finds that extreme weather like killer storms and high-rising seas could be mere decades, not centuries, away.
The report, "Ice Melt, Sea Level Rise, and Superstorms" [pdf] published Tuesday in the journal Atmospheric Chemistry and Physics, says that the 2-degree Celsius (or 3.6 degrees Fahrenheit) global warming threshold previously agreed upon by global leaders and scientists is too high. The research in the 52-page report is derived from observations of ancient climate change -- "paleo-climatology" -- as well as observations of current climate shifts, and data from computer modeling to forecast where the planet is headed.
"So, the question arises again: Have we passed the point of no return?" asked lead author James Hansen, a former NASA climate scientist, in a video message that accompanied the study release.
Hansen said that preventing such dire outcomes is all dependent on how quickly we act to "slow down" man-made climate change.
"I think the conclusion is clear, we are in a position of potentially causing irreparable harm to our children, grandchildren, and future generations," he said in the video.
So, what does the paper's doomsday scenario look like? The research points to the significant melting of Greenland and Antarctic ice sheets happening so quickly that they lead to as much as several meters of sea level rise within the next 50 to 150 years.
What will happen during this time is a "stratification" of the polar oceans, with a pool of cooler meltwater trapped at the ocean's surface while warmer water rests just underneath. This is dangerous, the paper argues, because the warmer water layer would hit the base of the polar ice sheets, melting them from below. This would result in accelerated ice melting and continued stratification, along with more rapid sea level increases.
Unfortunately, as you go through the paper, the news gets worse and worse. The North Atlantic area would actually cool, creating a bigger disparity between the ever-warming equatorial region, which in turn whips up huge storms and giant ocean waves.
"Many of the most significant and devastating storms in eastern North America and western Europe, popularly known as superstorms, have been winter cyclonic storms, though sometimes occurring in late fall or early spring, that generate near-hurricane-force winds and often large amounts of snowfall," the report states. "Continued warming of low-latitude oceans in coming decades will provide a larger water vapor repository that can strengthen such storms."
None of this is unprecedented. Hansen's team looked at events traced by paleoclimate scientists and geologists who determined that similar climate events took place 80,000 to 130,000 years ago, when temperatures warmed before the last ice age.
During that period, storms were so powerful they generated waves 40 meters (130 feet) high that could pick up and hurl huge boulders inland. "On rocky, steep coasts, giant limestone boulders were detached and catapulted onto and over the coastal ridge by ocean waves," the report says. [more]
By Justin Gillis
22 March 2016
(New York Times) – The nations of the world agreed years ago to try to limit global warming to a level they hoped would prove somewhat tolerable. But leading climate scientists warned on Tuesday that permitting a warming of that magnitude would actually be quite dangerous.
The likely consequences would include killer storms stronger than any in modern times, the disintegration of large parts of the polar ice sheets and a rise of the sea sufficient to begin drowning the world’s coastal cities before the end of this century, the scientists declared.
“We’re in danger of handing young people a situation that’s out of their control,” said James E. Hansen, the retired NASA climate scientist who led the new research. The findings were released Tuesday morning by a European science journal, Atmospheric Chemistry and Physics.
A draft version of the paper was released last year, and it provoked a roiling debate among climate scientists. The main conclusions have not changed, and that debate seems likely to be replayed in the coming weeks.
The basic claim of the paper is that by burning fossil fuels at a prodigious pace and pouring heat-trapping gases into the atmosphere, humanity is about to provoke an abrupt climate shift.
Specifically, the authors believe that fresh water pouring into the oceans from melting land ice will set off a feedback loop that will cause parts of the great ice sheets in Greenland and Antarctica to disintegrate rapidly. […]
The paper, written by Dr. Hansen and 18 other authors, dwells on the last time Earth warmed naturally, about 120,000 years ago, when the temperature reached a level estimated to have been only slightly higher than today. Large chunks of the polar ice disintegrated then, and scientists have established that the sea level rose 20 to 30 feet.
Climate scientists agree that humanity is about to cause an equal or greater rise in sea level, but they have tended to assume that such a large increase would take centuries, at least. The new paper argues that it could happen far more rapidly, with the worst case being several feet of sea-level rise over the next 50 years, followed by increases so precipitous that they would force humanity to beat a hasty retreat from the coasts.
ABSTRACT: We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.