Have tipping points already been passed for critical climate systems? (6) Permafrost: Beyond the models

by David Spratt 

Sixth in a series.    Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Permafrost is permanently frozen ground. It covers one-quarter of the land mass of the northern hemisphere, and contains 1.5 trillion tonnes of carbon, twice the amount currently in the atmosphere and triple the amount emitted by human activity since 1850.  Permafrost buried beneath the Arctic Ocean holds 60 billion tons of methane (in structures known as methane clathrates) and 560 billion tons of organic carbon.

Permafrost is releasing significant amounts of greenhouse gases, and feedbacks are under way, but the dynamics are not yet well enough understood to be able to judge whether tipping points have been reached or not.  As previously noted (in part 1 of this series), University of NSW researchers point out that: “We do not know exactly how close we are to a tipping point, or even whether we have already passed it… There are tipping points that while not yet triggered may already be fully committed to.” 

Have tipping points already been passed for critical climate systems? (5) Coral Reefs: A death spiral

by David Spratt 

Fifth in a series.    Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Updated 2 February 2022.

Great Barrier Reef bleaching 2016

Ecosystems, including coral reefs, mangroves and kelp forests in Australia, are degrading fast as the world's sixth mass extinction gathers pace. 

Coral polyps are invertebrates similar to minute jellyfish, which build limestone structures, and live in a symbiotic relationship with algae-like unicellular zooxanthellae that reside within the coral structure, and give it colour. The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, zooxanthellae supply the coral with oxygen, glucose, glycerol, and amino acids, which are the products of photosynthesis. 

Have tipping points already been passed for critical climate systems? (4) Forests and the Amazon: A faltering carbon sink

by David Spratt

Fourth in a series.    Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Deforestation in the Brazilian Amazon.
Image: Chatham House
 

 

The plant-based terrestrial biosphere may be understood as including the world’s land-based plants, soils, derived dead organic matter, such as litter, and soil organic matter. 

Plants photosynthesis uses carbon dioxide and water to produce sugar (glucose) and oxygen. Around 30% of the additional carbon dioxide (CO₂) produced by human actions has been drawn down from the atmosphere (mitigated) by increased plant photosynthesis. This adds to the land-based sink of stored carbon. But plants also respire, for example at night and in winter, by converting oxygen and stored glucose back into water and carbon dioxide. 

As the planet continues to warm, a point of warming is reached — the “thermal maximum for photosynthesis” — after which combination of the rate of photosynthesis decreasing and the rate of respiration increasing results in the net flux of CO₂ from the atmosphere decreasing.

Have tipping points already been passed for critical climate systems? (3) Greenland and the Arctic: Abrupt change

by David Spratt

Third in a series.    Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Broken-up Arctic sea-ice

“The Arctic is screaming”, says Mark Serreze, Arctic climate expert at the US National Snow and Ice Data Center.

Arctic warming is racing ahead of the worst-case estimates, now heating four times faster than the global average, and the region is undergoing abrupt climate change, understood as a transition of the climate system into a different mode on a time scale that is faster than the responsible forcing. In other words, it has passed a tipping point for rapid, system-level change. 

Researchers say that the Arctic “is currently experiencing an abrupt climate change event …  climate models underestimate the abruptness of the recent changes observed in the Arctic (and) climate models underestimate this ongoing warming”. [Models do not account well for warming due to sea-ice loss, but losing the reflective power of Arctic sea ice in the summer months would advance the 2ºC threshold by 25 years”.]

Have tipping points already been passed for critical climate systems? (2) West Antarctica and the "doomsday" glacier

 by David Spratt

Second in a series.    Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Thwaites Glacier fractures. Image: NASA

The Thwaites Glacier in West Antarctica has an eastern ice shelf 45 kilometres wide as it flows into the Amundsen Sea. On 13 December 2021, scientists announced that the ice shelf is likely to break apart in the next five years or so, resulting in a speeding up of the glacier’s flow and ice discharge, possibly heralding the collapse of the glacier itself, and triggering similar increases across the Amundsen Sea glaciers.

The researchers explain: “Over the last several years, satellite radar imagery shows many new fractures opening up… which like a growing crack in the windshield of a car [can] suddenly break apart into hundreds of panes of glass. We have mapped [the] pathway the fractures might take through the ice [and conclude] the final collapse of Thwaites Glacier’s last remaining ice shelf may be initiated … within as little as five years” (emphasis added).

Have tipping points already been passed for critical climate systems? (1) The basics

by David Spratt

First in a series.   Read 1  |  2  |  3  |  4  |  5  |  6  |  7

Tipping points and potential cascade effects

As global heating reduces the extent of floating Arctic sea-ice each summer, the heat-reflecting ice is replaced by heat-absorbing dark ocean water, adding energy to the Arctic system, driving more melting. This is a “positive feedback”, a self-reinforcing change. Examples abound in the climate system. On Greenland, for example, warming is reducing the height of the ice, and this lower elevation means it will melt more, because the temperature is higher at lower altitudes. 

Sixteen years ago, James Hansen warned that “We live on a planet whose climate is dominated by positive feedbacks, which are capable of taking us to dramatically different conditions. The problem that we face now is that many feedbacks that came into play slowly in the past, driven by slowly changing forcings, will come into play rapidly now, at the pace of our human-made forcings, tempered a few decades by the oceans thermal response time."