Climate tipping points that might already have been reached

As storms and fires become increasingly frequent and devastating, we are bombarded with more, increasingly alarming articles about climate change. Yesterday I wrote an introduction to climate tipping points. I did that because I came upon an interesting paper that goes into detail about three tipping points that might already have been reached.

In a 2019 paper, Professor Timothy Lenton, a global leader on the subject, identified nine climate tipping points, from melting permafrost in the Arctic to the loss of tropical coral reefs. Here we will focus on what he deems the three most critical tipping points: the Amazon rainforest, the West Antarctic ice sheet and the Gulf Stream system.

Lenton highlights these three because the West Antarctic ice sheet may have already passed a tipping point; the Amazon because it is a crucial crucible of biodiversity and for its warehouse of carbon; and the Gulf Stream system because of its potential for profound changes with connected ramifications all around the planet.

CBS News spoke to Lenton and several other scientists about the state of climate tipping points. While they have different areas of expertise, ranging from oceans to atmosphere to biosphere, their message was unanimous: Changes are happening faster than what was expected and the chance of hitting tipping points in the climate system, which just a decade ago appeared remote and far off, now seems much more likely and more immediate.

“This is why I have been raising the alarm,” Lenton said. “In just a decade the risk level has gone up markedly — that should be triggering urgent action.”

Climate tipping points may have been reached already, experts say
BY JEFF BERARDELLI, CBS News, APRIL 26, 2021

 Climate tipping points –too risky to bet against. The growing threat of abrupt and irreversible climate changes must compel political and economic action o emissions by Timothy Lentan et al, Nature, Nov 27, 2019

The Amazon rainforest

Deforestation and climate change are destabilizing the Amazon — the world’s largest rainforest, which is home to one in ten known species. Estimates of where an Amazon tipping point could lie range from 40% deforestation to just 20% forest-cover loss8. About 17% has been lost since 1970. The rate of deforestation varies with changes in policy. Finding the tipping point requires models that include deforestation and climate change as interacting drivers, and that incorporate fire and climate feedbacks as interacting tipping mechanisms across scales.

Climate tipping points –too risky to bet against. The growing threat of abrupt and irreversible climate changes must compel political and economic action o emissions by Timothy Lentan et al, Nature, Nov 27, 2019

Having studied the Amazon for 56 years and visited hundreds of times, Dr. Thomas Lovejoy is one of those experts. 

“We are really right at that tipping point. We see the signs in longer dry seasons, hotter dry seasons, tree species that prefer drier conditions gaining dominance over those that prefer wet conditions,” explains Lovejoy, a professor at George Mason University and founder of the Amazon Biodiversity Center. “So we know that it’s right there at the tipping point right now.”

When Lovejoy started studying the Amazon in the 1960s, 10 million people lived there and the forest was 97% intact. Now there are 30 million people living there and deforestation in the Brazilian Amazon is at 20% — the critical level at which scientists believe the Amazon starts to tip towards the point of no return, where it no longer survives as a lush wet rainforest and transitions into an arid savanna.

Lovejoy says this transition from rainforest to savanna could happen as fast as a mortgage cycle. “I would say it’s a matter of something that happens on the timescale of decades like 10, 20, 30 years, not centuries. So, a lot of the people alive today would actually get to see that negative consequence.” 

Climate tipping points may have been reached already, experts say
BY JEFF BERARDELLI, CBS News, APRIL 26, 2021


West Antarctic ice sheet

The latest research finds that global warming thresholds that would trigger tipping points on both the Greenland and Antarctic ice sheets are not that far away. The authors of a 2018 study find that these tipping points will likely occur between 1.5 and 2 degrees Celsius of global warming above pre-industrial levels — the level at which the Paris Climate Agreement aims to halt warming. The Earth has already warmed by 1.2 degrees, and 1.5 degrees of warming may be less than 15 years away.

Of all the threats posed by climate change, sea level rise is arguably the biggest. That’s because with billions of people living along the world’s coastlines, rapid sea-level rise will force massive disruption. Given the immense amount of heat already absorbed in the ocean system due to human-caused climate change, there’s no doubt several feet — and likely much more — of sea level rise is already locked in, but the question is how fast will it happen?

Climate tipping points –too risky to bet against. The growing threat of abrupt and irreversible climate changes must compel political and economic action o emissions by Timothy Lentan et al, Nature, Nov 27, 2019


Research in the past decade has shown that the Amundsen Sea embayment of West Antarctica might have passed a tipping point3: the ‘grounding line’ where ice, ocean and bedrock meet is retreating irreversibly. A model study shows5 that when this sector collapses, it could destabilize the rest of the West Antarctic ice sheet like toppling dominoes — leading to about 3 metres of sea-level rise on a timescale of centuries to millennia. Palaeo-evidence shows that such widespread collapse of the West Antarctic ice sheet has occurred repeatedly in the past.

The Greenland ice sheet is melting at an accelerating rate3. It could add a further 7 m to sea level over thousands of years if it passes a particular threshold. Beyond that, as the elevation of the ice sheet lowers, it melts further, exposing the surface to ever-warmer air. Models suggest that the Greenland ice sheet could be doomed at 1.5 °C of warming3, which could happen as soon as 2030.

Climate tipping points –too risky to bet against. The growing threat of abrupt and irreversible climate changes must compel political and economic action o emissions by Timothy Lentan et al, Nature, Nov 27, 2019


The Gulf Stream system 

Lenton described a potential tipping point in the Gulf Stream system as “profound.” That’s because the Atlantic Ocean circulation is a linchpin in Earth’s climate system. It is the driving force behind the Global Ocean Conveyor Belt (pictured below) and transports 20% of the excess heat which accumulates at the Equator towards the Northern Hemisphere polar regions. This is how Earth attempts to balance out unequal heating from the sun, and the flux of heat is a big factor controlling weather patterns. 

What concerns scientists is that this current is slowing down. In fact, a new study found it is moving the slowest it has in at least 1,600 years and may decrease speed by up to 45% by 2100, possibly tipping the circulation into collapse. 

ocean-conveyor.png
Climate tipping points may have been reached already, experts say
BY JEFF BERARDELLI, CBS News, APRIL 26, 2021

Before we go any further, it is worth mentioning that the Gulf Stream system is a newly popularized nickname for the Atlantic Meridional Overturning Circulation (AMOC for short). One look at that name and it’s clear why the Gulf Stream system may be preferable. 

But in that AMOC name there are some clues as to why this current system is so important. “Meridional” means transport in a north-to-south or south-to-north direction. And “overturning” implies that the current moves vertically as well. So this current is the engine that propels ocean heat to the ends of the Earth. 

gulf-stream-current-2.jpg
Climate tipping points may have been reached already, experts say
BY JEFF BERARDELLI, CBS News, APRIL 26, 2021

Climate tipping points may have been reached already, experts say
BY JEFF BERARDELLI, CBS News, APRIL 26, 2021

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