Is global warming faster than expected? / John Kerry

Ice loss, permafrost thaw and climatic effects are occurring at an alarming rate.

In the past decade, scientists believed they had found a way to protect humanity from the more serious dangers of climate change. In their estimation, maintaining a global warming level of less than two degrees Celsius will prevent dangers such as a devastating rise in sea level or extreme drought. Staying below the two-degree limit would require limiting the level of heat-trapping carbon dioxide in the atmosphere to 450 parts per million (ppm) compared to 395 today and 280 in pre-industrial times.

It now appears that the assessment was too optimistic. The latest data from around the world show that the earth is changing faster than expected. Floating glaciers in the Arctic Ocean region are disappearing to a greater extent than predicted, and permafrost areas in Alaska and Siberia are emitting methane, a highly influential greenhouse gas, much more than expected according to models. Ice shelves in West Antarctica are breaking off faster than previously thought possible, and the glaciers they have trapped on nearby land are sliding faster into the sea. Extreme weather events, such as floods and the great heat wave that hit most of the US in the summer of 2012, are also becoming more common. And the conclusion? "As scientists, we cannot say that if we stay below two degrees of warming everything will be fine," says Stefan Ramstorff, professor of ocean physics at the University of Potsdam in Germany.

To the website of the article in "Scientific American"

The unknown factors, which may degenerate the earth into a period of rapid climate change, are feedback loops, which until now have only been conjectured and are now apparently beginning to operate. For example, the shrinking of the floating glaciers allows the sun to warm the ocean water more, leading to more melting of the glaciers. The thawing of the permafrost releases more carbon dioxide and methane into the atmosphere, which causes further thawing of the permafrost, and so on.

The possibility of feedback acceleration has caused some scientists to become vocal prophets of rage. These experts say that even if the countries suddenly took seriously the problem of reducing greenhouse gas emissions and kept them below 450 parts per million, which seems less and less likely, it would still be too little too late. If the world does not return carbon dioxide levels to 350 parts per million, "we will start a process that is beyond the control of humanity," warns James A. Hansen, director of NASA's Goddard Institute for Space Studies. According to him, the height of the sea water may rise up to 5 meters in this century, and coastal cities from Miami to Bangkok will sink under the water. The increasing heat and drought will cause a massive famine. "The consequences are almost indescribable," continues Hansen. We may be on the verge of a big and irreversible leap into a much warmer world.

Is this a false alarm? Some scientists think so. "I don't think that a catastrophic change in climate is expected in the short term," says Ed Delugokenki of NOAA (US National Oceanic and Atmospheric Administration), basing his assessment on methane levels. Glaciologist W. Ted Pepper from the University of Colorado in Boulder examined the loss of ice around the world, and his conclusion is that the maximum increase in the level of the ocean that is possible this century is less than 2 meters, not 5 meters. However, he shares Hansen's sense of urgency, because even relatively small changes could threaten a civilization that has known only remarkably stable climates throughout its existence. "The public and decision makers need to understand how serious a rise of even 60 or 70 centimeters in sea level would be," Pepper warns. "These creeping disasters can destroy us."

Scientists may disagree on the pace of climate change, but the recognition that certain feedback loops may be amplifying change is causing great uneasiness about the planet's future. "We have to think deeply about impacts we know we don't understand, and impacts we don't know at all," says Ilko Rowling, professor of oceanography and climate change at the University of Southampton in England. "We may not know all the possible feedbacks, but changes that happened in the past show that they exist." Martin Manning, an atmospheric scientist at Victoria University in Wellington, New Zealand, fears that by the time researchers identify all the unknown factors, it will be too late. Manning, who played a central role in the 2007 Intergovernmental Panel on Climate Change (IPCC), reports: "The rate of change in this century will be such that we cannot wait for the science."

A warm past indicates a warm future
One major reason for scientists' growing concern about rapid climate change is a better understanding of our distant past. In the 80s they were amazed to discover, from records in ice cores, that the planet repeatedly experienced sudden and sharp fluctuations in temperature. Since then they have produced a detailed picture of the last eight hundred thousand years. As Hansen described in a new analysis, there is a very close relationship between temperature, carbon dioxide levels and sea level: they rise and fall together, almost as one body. The correlations do not prove that greenhouse gases cause warming. However, a new study by Jeremy Chacon of Harvard University and his colleagues points in this direction and shows that the increase in carbon dioxide preceded the spike in temperatures at the end of the last ice age. In a recently published article in Nature, they conclude that "warming resulting from an increase in the concentration of carbon dioxide explains most of the temperature changes." (Scientific American is part of the Nature publishing house, NPG).
Some of the changes in the past were unbelievably fast. A study conducted by Rowling on sediments in the Red Sea shows that during the last warm period between ice ages - about 125 thousand years ago - the sea level rose and fell by 2 meters within 100 years. "It's ridiculously fast," says Rowling. His analysis shows that the sea level was probably 6 meters or more higher than it is today, and in a climate very similar to ours. "It doesn't tell what will happen in the future, but it gets attention," says Richard Ely, professor of earth sciences at Pennsylvania State University.

It is also amazing how little additional energy, or "push", was required to cause oscillations in the past. For example, 55 million years ago, the Arctic was a subtropical paradise with a comfortable average temperature of 23 degrees Celsius and alligators in the Greenland region. The tropics were probably too hot for most living things. This warm period, known as the Paleocene-Eocene Epoch Heat Wave (PETM), began because of a two degree increase in the Earth's temperature, which was also warmer than today. It is possible that this warming caused a rapid release of methane and carbon dioxide, and these caused more warming and additional emission of greenhouse gases, which strengthened the process. The end result: millions of years of a hot Earth.
In the last hundred years, humans have caused a temperature jump of more than 0.8 degrees, and we are emitting greenhouse gases into the atmosphere at a rate ten times greater than before the PETM, giving the climate a very strong boost. "If we burn carbon for the next 100 years, we'll make the same jump," says Matthew Huber, a professor of earth and atmospheric sciences at Purdue University.

We are also pushing the climate harder than the known causes of the various ice ages. As the Serbian astronomer Milotin Milankovic pointed out almost 100 years ago, there is a connection between the rise and fall of the ice ages and slight changes in the Earth's orbit and tilt. Over tens of thousands of years, the Earth's orbit changes its shape from a nearly perfect circle to a slightly elliptical one, due to the changing pull of other planets. These changes change the amount of solar energy that hits the Earth's surface by an average of 0.25 watts per square meter, Hansen says. It's not much. To cause the observed fluctuations in climate, this push had to be amplified by feedbacks, such as changes in floating glaciers and greenhouse gas emissions. In previous warmings, "feedback led to feedback that led to feedback," says Ewan Nisbet, professor of earth sciences at Royal Holloway, University of London.

Pushing the climate by human-caused greenhouse gas emissions is much greater - three watts per square meter, and the number is only increasing. Will the climate change twelve times faster? Not necessarily. "It is impossible to project from the reaction in the past as it is into the future," Rowling explains. "We are learning what mechanisms are at work, what triggers them and how severe they might be."

Disturbing feedback
Scientists have discovered that the fastest feedback mechanism involves ocean currents that carry heat to the surface of the Earth. If a large amount of fresh water is added to the North Sea, for example, as a result of the collapse of glaciers or an increase in the amount of rain - the warm currents may slow down or stop, thus disrupting the driving force of the global currents in the oceans. This change will cause Greenland to warm within a decade. "The ice core records from Greenland show that changes can happen very quickly, even within 10 years," says Peter Tenes, chief scientist at NOAA's Earth System Research Laboratory.
When in the early 2000s the freshwater mechanism was clarified, "many of us were very tense," Eli says. However, according to him, more detailed models have shown that "adding fresh water is indeed a scary thing, but we are not adding it fast enough" to fundamentally change the Earth's climate.

A more troubling short-term feedback, which is starting to literally come to the surface, is related to permafrost soils. In the past, scientists believed that the organic matter in the tundra reached a depth of only one meter in the frozen ground, and that it would take a long time for warming to begin to thaw significant amounts of it at depth. According to new research, this assessment was wrong. "Almost everything we recorded surprised us," says biologist Ted Shore of the University of Florida.

The first surprise was that organic carbon is found up to a depth of about 3 meters, so there is more of it. Moreover, Siberia is dotted with huge hills of frozen soil rich in organic matter, called "Yedoma" and originating from wind drifts from China and Mongolia. These carbon stocks amount to hundreds of billions of tons, "roughly twice the amount that is currently in the atmosphere," Shore says. Or, as methane hunter Joe Von Fischer of Colorado State University puts it: "This carbon is one of those ticking time bombs." The thawing allows more bacteria to digest the organic carbon and turn it into carbon dioxide and methane, which will lead to rising temperatures and further thawing.

The bomb may be ticking at a faster rate. Water from thawing often accumulates as shallow lakes on the permafrost. Katie Walter Anthony of the University of Alaska at Fairbanks discovered methane bubbling up from the bottom of the lakes. Many researchers have also found that permafrost may crack into small canyons, called thermokarsts that expose much larger surface areas to the air and thereby accelerate thawing and the release of greenhouse gases. Expeditions that recently went to Spitsbergen in Norway and Siberia discovered methane clouds rising from the ocean floor in shallow places.

If these gas emissions infer what's happening in larger areas, the numbers could be big enough to shock the climate. However, recent global measurements of methane do not necessarily show a recent increase. One of the reasons is that the emission points "are still relatively localized," says Vladimir A. Romanovsky of the University of Alaska, who deals with temperature mapping of permafrost soil. Another possible reason is that scientists have simply learned to better locate emission points that have always existed. Therefore, "I'm not worried about rapid climate change originating from changes in methane," says Dlugokenki.
Others doubt his words, mainly because there is another large potential source of methane: tropical wetlands. If the amount of rain in the tropics increases, as is expected to happen if the temperature rises, these marshes will grow and become more active, with more methane-producing anaerobic decay. Enlarged marshes will release the same or greater amount of methane from the Arctic warming vent. Should we be worried? "We don't know, but we better keep checking," says Nisbet.

The ice effect
The feedback that scares many climate scientists the most is global ice loss. For example, the dramatic shrinking of sea ice in the Arctic Ocean in recent summers was not predicted by many climate models. "This is the big failure of the models," says Nisbet. Ice is also disappearing in Greenland and Antarctica.

To understand what's going on, scientists have mapped glaciers in Greenland using satellite and ground measurements, and placed sensors under the Antarctic ice shelves, "that see things that have never been seen before," says Jerry Meehl, a senior scientist at the US National Institute for Atmospheric Research.

In Greenland, glacier researcher Sarah Dess of the Woods Hole Oceanographic Institution watched a lake, which originated from ice melt water, drain suddenly into a crevice in an ice sheet 900 meters deep. The flow was strong enough to lift the heavy glacier off the bedrock beneath it and increase its gliding speed into the ocean. Data collected by Pepper in Alaska show that the sliding of the huge Columbia Glacier into the sea has accelerated from 15 meter per day to 20 to XNUMX meters per day.

In Antarctica and Greenland, large ice shelves floating in ocean water along the coast are collapsing - a reminder of their instability. Warmer ocean water gnaws at these ice shelves from below, and warm air creates grooves in them from above. These shelves act as buttresses, preventing ice anchored to the ocean floor and glaciers at the land's edge from sinking into the sea under gravity. The melting of floating ice does not raise the water level, but sinking glaciers will. "We are working hard to find out if the rise in sea level could be much faster than expected," says Eli.

The fear of ice loss is not only related to sea level rise, but also to the activation of a powerful feedback mechanism. The ice reflects sunlight into space. Without it, the earth and the dark water from it will absorb more heat from the sun, and more ice will melt. This change in the Earth's surface albedo could explain how slight spurts in the climate record were amplified, says Hansen, "and the same thing will happen today."

So far, only a few scientists are willing to predict, like Hansen, that the oceans will rise by 5 meters by the year 2100, "but we don't know for sure," Eli says. "I still think the odds are in my favor [expecting a more modest increase], but I don't want anyone buying real estate in the coastal area based on what I'm saying."

A forest for the trees

The fluctuations in Earth's climate in the past prove that if we push hard enough, feedbacks will radically change the planet. "If we burn all the carbon we can get, we'll definitely get PETM-like warming," says Huber. It's good, maybe, for arctic alligators, but not for humans and most ecosystems.

However, what really keeps scientists awake is the possibility that, even if these specific feedbacks do not pose a threat to humanity in the near term, they could set in motion other threatening mechanisms. A leading candidate is the global water cycle. Each year, more evidence accumulates that climate change is causing more extreme weather events, such as floods and droughts, while fundamentally altering local climates.

A recent analysis by Ramstorf shows that heat waves, like the one that hit Russia in 2010, are five times more likely to happen due to the warming that has already occurred - "a very significant factor," he said. A new study blames the record-breaking warm winter of 2011-2012 in the United States (and the unprecedented cold in Europe at the same time) to the loss of Arctic sea ice. One of the proposed mechanisms is this: the less sea ice there is, the warmer the arctic water gets. The ocean emits excess heat in the fall and changes the temperature patterns in the atmosphere. These cause larger twists in the jet stream, which may remain in place for a longer time. These meanders bathe the Northeastern US in winter heat, while Eastern Europe is trapped in a deep freeze.

The story is further complicated by the potential for ecological feedback. Rising temperatures in the western US and Canada, for example, helped spread an epidemic of mountain pine beetles. These insects have destroyed hundreds of thousands of dunams of trees, and they threaten to turn the forests from carbon traps (healthy trees absorb carbon dioxide) to carbon sources (decay of dead trees). A fire in 2007 led to the first fire in seven thousand years in the tundra of the North Slopes in Alaska, which accelerated the thawing of permafrost soils in the region and the carbon emissions from them. Warming in Siberia is beginning to turn large cedar forests into forests of spruce and fir. The cedar sheds its needle-like leaves in the winter, allowing the sun's heat to reflect in the snow layer and return to space. The firs, on the other hand, are not deciduous, and they absorb the sun's heat before it reaches the snow. This is how the ecologist Hank Shugart from the University of Virginia explains. In his estimation, the feedbacks from vegetation changes alone can raise the temperature of the earth by a degree and a half: "We are playing here with a loaded gun."

Nisbet's "horror scenario" begins with an increase in methane emissions, and a very hot summer that causes large fires and the emission of a lot of carbon into the atmosphere. The blanket of smoke and soot envelops Central Asia and weakens the monsoons, causing widespread crop destruction in China and India. At the same time, a large "El Nino" pattern with extremely warm water in the tropical Pacific Ocean causes drought in the Amazon region and Indonesia. The tropical forest and peatlands are catching fire, adding even more carbon dioxide to the atmosphere and rapidly accelerating global warming. "This is a plausible scenario," says Nisbet. "We may be more fragile than we think."

How strong can the various feedback loops be? Climate models, which succeed in explaining the past and the present, fail when they have to predict the future. "People can capture these sudden changes better than the models," Shore says. According to him, even if the planet is at a turning point, it is doubtful that we will be able to detect it.

The alarming conclusion in terms of climate policy is that science does not have absolute answers. "We know the direction but not the pace," says Manning. However, the scientists strongly argue that uncertainty does not justify inaction. On the contrary, the uncertainty emphasizes the need for an immediate global effort to reduce greenhouse gas emissions, because it reveals how serious the risks of rapid warming are. "We are actually now conducting an experiment comparable, on a geological scale, to the great events of the past. Therefore, we can expect results similar to those obtained in the past," says Nisbet.

This is the reason why Hansen is unable to look at his grandchildren without becoming an active environmentalist for them. "It would be immoral," he says, "to leave these young people with a climate system spinning out of control."

And more on the subject
Abrupt Climate Change. US Climate Change Science Program and the Subcommittee on Global Change Research. US Geological Survey, December 2008. http://downloads.climatescience.gov/sap/sap3-4/sap3-4-final-report-all.pdf

Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Working Groups I and II of the Intergovernmental Panel on Climate Change. Cambridge University Press, 2012. http://ipcc-wg2.gov/SREX/images/uploads/SREX-All_FINAL.pdf

Paleoclimate Implications for Human-Made Climate Change. James E. Hansen and Makiko Sato in Climate Change: Inferences from Paleoclimate and Regional Aspects. Edited by André Berger et al. Springer, 2012.

www.youtube.com/watch?v=YegdEOSQotE
Video by Katie Walter Anthony of the University of Alaska at Fairbanks of methane from thawed permafrost catching fire: