Notes From an Environmentalist; The biggest environmental problem facing us, how many tipping points have we passed or are about to pass?

Tipping Points for the Planet

Complex environmental systems are undergoing profound upheavals as a result of human activity.

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A fire in a tropical-looking forest. Flames are consuming grass in the foreground. In the background, dark smoke shrouds tall trees.

Burning to create pastureland for cattle in Mato Grosso State, Brazil.Credit...Victor Moriyama for The New York Times

David GellesManuela Andreoni

By David Gelles and Manuela Andreoni

Feb. 15, 2024

A drumbeat of recent reports has driven home the fact that our planet’s complex environmental systems are undergoing profound upheavals as a result of human activity.

Glaciers around the world, from Greenland to Switzerland to Antarctica, are melting faster than expected as atmospheric and ocean heat hit new highs.

New research suggests that up to half of the Amazon rainforest could rapidly transform into grasslands or weakened ecosystems in the coming decades as a result of deforestation, climate change and drought. Those stresses could eventually drive the entire forest ecosystem, home to a tenth of the planet’s land species, past a tipping point that would trigger a forest-wide collapse.

And a new study suggests that a crucial network of ocean currents that carries warm water into the North Atlantic is showing early signs of collapse because of an influx of fresh water from melting glaciers.

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All of these developments appear worrisome on the surface. But, most concerning of all, they raise the specter that the planet may be approaching some of the so-called tipping points that could trigger severe and irreversible changes.

Tim Lenton, a professor who studies climate and Earth systems at the University of Exeter, said tipping points were characterized by “amplifying feedback within a system that’s getting strong enough that it can cause a self-propelling change.”

What that means in layman’s terms: Once the key threshold is crossed, the change accelerates, and a profound transformation becomes inevitable. Change begets more change in a self-reinforcing loop.

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Amazon rainforest. Up to half of the Amazon rainforest could transform into grasslands or weakened ecosystems in the coming decades, a new study found, as climate change, deforestation and severe droughts damage huge areas beyond their ability to recover. Those stresses in the most vulnerable parts of the rainforest could eventually drive the entire forest ecosystem past a tipping point that would trigger a forest-wide collapse, researchers said.

A significant threshold. Over the past 12 months, the average temperature worldwide was more than 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, higher than it was at the dawn of the industrial age. That number carries special significance, as nations agreed under the 2015 Paris Agreement to try to keep the difference between average temperatures today and in preindustrial times to 1.5 degrees Celsius, or at least below 2 degrees Celsius.

New highs. The exceptional warmth that first enveloped the planet last summer is continuing strong into 2024: Last month clocked in as the hottest January ever measured, and the hottest January on record for the oceans, too. Sea surface temperatures were just slightly lower than in August 2023, the oceans’ warmest month on the books.

A revised history. Scientists have examined the chemical composition of the skeletons of centuries-old spongy sea creatures living in the Caribbean Sea to piece together a new history of the earliest decades of global warming. The research points to a startling conclusion: Humans have raised global temperatures by a total of about 1.7 degrees Celsius, or 3.1 Fahrenheit, not 1.2 degrees Celsius, as widely suggested until now.

A giant parasol in outer space? With Earth at its hottest in recorded history, and humans doing far from enough to stop its overheating, a small but growing number of astronomers and physicists are proposing a fix that could have leaped from the pages of science fiction: the equivalent of a giant beach umbrella, floating in outer space.

There is no consensus that any large-scale tipping points have been reached, though there is debate about whether some, on the Greenland ice sheet and in many of the world’s coral reefs, are close or have already tipped.

“Things that we actually observe happening in the climate look a whole lot like tipping point changes, or serious harbingers of those changes,” Lenton said.

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The planet’s tipping points

The phrase “tipping point” has a complicated and controversial history. Scientists started talking regularly about climate tipping points in the early 2000s. They quickly concluded that some of those tipping points were fast approaching, or might have already passed.

The self-propelling mechanism of tipping points are typically made up of various feedback loops. Here are examples of how some of them work.

Some of the most worrisome concern the world’s vast ice sheets. If the Greenland ice sheet collapses, for example, global sea levels could rise by seven meters, or 23 feet, over the next centuries. Feedback loops: As the ice melts, its surface declines in altitude, which means the air on top of it is warmer, leading to more melting. And, disappearing ice means fewer white surfaces to reflect sunlight back into space, which warms the atmosphere even more.

Thawing of permafrost could release gigatons of planet-warming methane into the atmosphere. Feedback loop: Methane causes the atmosphere to warm further, melting more permafrost, and so on.

Earth’s ecosystems — such as forests, coral reefs and lakes — are in danger, too, with far-reaching consequences. For example, the collapse of boreal forests, which burned at an unprecedented rate last year, could send enormous amounts of carbon into the atmosphere. Feedback loop: Fires create water stress, reducing the ability of trees to resist insect infestation, which makes them more vulnerable to fires.

Currents and monsoons that regulate the oceans and the atmosphere can slow down, warm up and shift in all sorts of ways. If the currents that bring warm water to the North Atlantic collapse, for example, average temperatures in Western Europe could plummet in a matter of decades. Feedback loop: These currents move saltier water from one part of the ocean to another. If they become weaker, less salt is transported, the surface water becomes less salty, which makes it less dense and less likely to sink, weakening currents further.

Since researchers started identifying tipping points, the list of systems that are close to the edge has grown steadily to the current two dozen; some closer, some farther from collapse. You can check them all out in a report about global tipping points that Lenton and his colleagues published a few months ago.

Good tipping points

It’s not only the planet that can experience tipping points. There are industrial, technological and economic tipping points, too. And some of them might help curb global warming.

Take the rapid decline in costs for renewable energy. Last year, we reported on a study that argued solar power had already passed a tipping point because market forces alone, with no help from policymakers, could make it the cheapest source of electricity by 2027. Similar dynamics could benefit wind power, batteries and other parts of the clean energy transition.

The new economics of green energy is leading to an influx of spending in the sector. Last year, for the first time, total global investments in solar were greater than investments in oil.

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Solar panels, wind turbines and batteries are all experiencing startling gains in efficiency, too. And, the adoption of electric vehicles and heat pumps continues to rise as they become more affordable.

Lenton, who is writing a book about tipping points, noted that social norms could rapidly change, as well, practically overnight. (The phrase “tipping point” was used in social science to describe a sudden rush of white families moving out of a given neighborhood as Black families moved in.)

Some people believe that we may see the animal farming industry we have today as unacceptable in the future. Could eating meat every day be frowned upon in the future? Will burning fossil fuels ever become unthinkable?

“Sometimes change really is self-propelling, and something huge happens out of nowhere,” Lenton said. “It could be really bad, if it’s bad. But it can also be very good, if it’s good.”