Climate tipping points: Do we still have time?

Those of us who read James Hansen’s Storms of My Grandchildren years ago have been haunted ever since by the vision of “tipping points” that would take climate change beyond human control. The term “tipping points” as used in climate science means the critical point in an evolving system beyond which the system shifts to a new state. The change is often abrupt and irreversible. The tipping points that would bring us abrupt and irreversible climate change are fueled by feedback loops that amplify global warming.

Our continued reckless burning of fossil fuels causes cumulative CO2   levels to rise. On April 26, 2017, CO2   levels reached 412.63 parts per million (ppm) as measured at the Mauna Loa observatory in Hawaii. Under President Trump, the US has left the Paris Climate agreement, and is already demolishing emissions rules for power plants, limits on methane leaks, and the moratorium on federal coal leasing.

We are now on a trajectory to to reach temperatures 4 to 6 degrees higher than pre–industrial levels by the end of the century. According to Kevin Anderson, Deputy Director of the Tyndall Center for Climate Change, “A four degree C future is incompatible with an organized global community, is likely to be beyond adaptation, is devastating to the majority of ecosystems, and has a high probability of not being stable.”

Can we still halt climate change at two degrees C, the internationally agreed threshold, beyond which lies catastrophe? According to Anderson, “No carbon tax is going to do that. We won’t get there through innovation or new technology, even if we spend a trillion a year for the next few years. The only conceivable way to produce that level of reductions is a full scale, all–hands-on-deck mobilization, what William James called ‘the moral equivalent of war.’”

Do we still have time before climate “tipping points” take global warming beyond our ability to prevent the breakdown of civilization, and the extinction of most of the plants and animals on the planet, including Homo sapiens?

Climate tipping points

The paleoclimatic record shows that abrupt climate shifts have happened many times in the past. During the past 110,000 years there have been at least 20 such abrupt climate changes. Only one period of stable climate has existed during this time—the 11,000 years of modern climate—the Holocene, the period of time that human beings have existed on this planet. Samples taken from ice cores, and ocean and lake sediments from around the world confirm that many sudden warmings and coolings of 8 degrees Celsius happened in less than 10 years. Ice core data show that during a period known as the Younger Dryas, Greenland warmed more than 8 degrees Celsius in less than a decade.

The Arctic Sea ice collapse

The tipping point that gives scientists nightmares because it could happen as early as 2030 is the Arctic sea ice collapse. The Arctic has been warming at three times the global average and the extent of the summer sea–ice has been shrinking dramatically. White snow and white sea–ice reflect sunlight back into space—this is known as the Albedo Effect. It may seem minor, but reductions in the Albedo Effect are a powerful driver of global warming. Snow reflects 90% of the sun’s rays back into space, while earth, rocks and the dark ocean absorb 90% of the sun’s rays, heating the planet. As sea–ice melts, the darker ocean absorbs more sunlight, amplifying warming. James Hansen, perhaps the world’s most preeminent climate scientist, warns that loss of Arctic sea ice creates a grave threat of passing two other tipping points—the instability of the Greenland ice sheet and the melting of ocean methane hydrates. “Two tipping points that would have consequences that are practically irreversible on time scales of relevance to humanity,” Arctic warming also has immediate effects. It changes the Northern Hemisphere jet stream. The Northern Hemisphere jet stream flows in wavy patterns from west to east, driven by the rotation of the earth and the difference in temperature between the equator and the North Pole. When the Arctic warms faster than the equator does, the jet stream can become slower, the waves deeper, and the west to east flow can stall for days. It may be one of the reasons Hurricane Harvey stalled over Houston for so long, bringing a record–breaking 51+ inches of rain.

Meltdown of the Greenland and West Antarctic ice sheets

Ice caps and glaciers along the coast of Greenland and the West Antarctic ice shelf passed tipping points more than a decade ago. An ice shelf is a largely submerged floating sheet of ice that often abuts a grounded glacier. Once the tipping point is passed, the complete disintegration of the ice sheet is inevitable, even without further warming. When ice shelves disintegrate, they speed the movement of the grounded glacier to the sea where exposure to warm water accelerates melting.  The breakup of ice sheets can be dramatic. You may remember the one trillion ton iceberg, the size of Delaware that calved from the Larsen C ice shelf last July, changing the landscape of Antarctica forever.

Although the complete meltdown of the ice covering the interior of Greenland, and the disintegration of the entire West Antarctic ice sheet is expected to take centuries, large scale deglaciation has begun, and the melting contributes to disastrous sea level rise.  Sea level has been rising faster than scientists predicted; and it is now accelerating, rising three times faster than it did twenty years ago. According to the National Oceanic and Atmospheric Administration’s 2017 report, sea level could rise more than 8 feet by 2100.  “There’s no argument about the fact that we will lose the coastal areas, now occupied by most of the large cities of the world,” warned Hansen. “It’s only a question of how soon. It’s hard to imagine that the world would be governable if this happened relatively rapidly.”

The cities most threatened by sea level rise are the Asian megacities with millions of inhabitants: Shanghai, Hong Kong, Mumbai, Calcutta, Jakarta, Ho Chi Minh City, Osaka, Tokyo, and Hanoi. But eight feet of sea level rise could inundate New York and obliterate Miami, southern Florida and downtown Olympia WA.

Melting Permafrost

Arctic warming is also melting permafrost across Alaska, Canada and Siberia faster than models had predicted. Vast areas of permanently frozen ground are beginning to thaw, releasing carbon dioxide and methane that has been locked in the subsoil for thousands of years. Permafrost is land that has been frozen for at least two years. Some Arctic permafrost has been frozen since the last ice age. About a quarter of the Northern Hemisphere is covered by permafrost and it ranges in thickness from about 1,300 feet in the north to less than a foot in southern permafrost regions. Scientists estimate that the Northern Hemisphere permafrost may contain twice as much carbon from decayed organic matter as is currently in the atmosphere. As the Arctic warms, the upper layer of permafrost (the active layer) thaws in the summer, releasing CO2  and methane, both powerful greenhouse gases. The release of CO2  and methane accelerates warming, which in turn, thaws more permafrost and releases more CO2  and methane in an amplifying feedback loop. The area of summer permafrost melt has been increasing significantly in coastal areas and eastern Canada.

Although most scientists believe that widespread changes to permafrost will take centuries, Anton Vaks, a scientist from the University of Oxford who has been measuring the melting rates of permafrost in Siberian caves, found that “global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.” Vaks says that “1.5 C appears to be something of a tipping point.”

Permafrost is also structurally important. When it melts it causes landslides and ground subsidence, buckling roads and railways. You have probably seen photos of the uneven ground subsidence in Alaska, making the structures in whole villages tilt and sink into the ground. Cracking and collapsing structures are a growing problem in cities like Norilsk , a Russian city located 180 miles above the Arctic Circle. You have probably also seen photos of the enormous craters found on the Siberian tundra. Although very little is known about the craters, scientists believe that they may be caused by methane explosively released from thawing Pingos (earth–covered mounds of permafrost).

Thawing methane hydrates

Methane (CH4) is the chief constituent of natural gas, the fossil fuel we use to heat our homes, the gas which accumulates in landfills. It is formed from decaying organic matter in the soil or on the ocean floor. It is found, not only in permafrost, but also in frozen methane hydrates, known as clathrates on shallow ocean shelves. Although Methane is 20 times more potent as a greenhouse gas than CO2  it lasts in the atmosphere only 12 years, while CO2  can remain in the atmosphere up to 200 years, with a small portion lasting thousands of years. Methane hydrates are methane gas frozen into ice structures. When methane hydrates melt, the methane can be released directly into the atmosphere, or bacteria can break it down into carbon dioxide.

“We don’t know the amount of methane frozen deep beneath the ocean,” says David Archer, a computational ocean chemist at the University of Chicago who has done research on ocean methane hydrate decomposition. “We do know that some methane deposits are seeping into the atmosphere, however.” Scientific expeditions have found methane plumes wider than one kilometer rising from the Arctic Ocean directly into the atmosphere. Methane released from ocean clathrates has the same amplifying feed–back effect as methane released from permafrost; it speeds global warming, which then melts more methane hydrates in a self–perpetuating cycle.

Potential clathrate destabilization in the Arctic is one of the most serious scenarios for abrupt climate change.

A 2016 review of scientific literature done by the US Geological Survey and the University of Rochester finds that gas hydrate breakdown is unlikely to cause a massive greenhouse gas release. The study concludes that current warming of ocean waters is likely causing gas hydrates to break down in some locations. However, not only are annual emissions to the ocean from degrading gas hydrates far smaller than greenhouse gas emissions to the atmosphere from human activities, but most of methane released by gas hydrates never reaches the atmosphere. Instead, the methane often remains in the undersea sediments, dissolves in the ocean, or is converted to carbon dioxide by microbes in the sediments or water column.   

Archer agrees. He has modeled what happens if methane is released continually for several decades. “So far,” he writes, “the sources of methane from high latitudes are small, relative to the big players: wetlands in warmer climates and human emissions. It is very difficult to know whether the bubbles are a brand–new methane source caused by global warming, or a response to warming that had happened over the past 100 years, or whether plumes like this happen all the time. …Thawing methane hydrates in the ocean and permafrost peats could be a significant multiplier of the long tail of the carbon dioxide, but it will probably not be a huge player in climate change in the coming century. The real point of no return in this adventure is our ongoing release of carbon dioxide.”

Bourtai Hargrove is a climate activist, a Socialist and a grandmother.

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