AGENDA

  • 21 September 2021
  • 10:00-10:30

Could Amazon deforestation trigger a climate tipping point?

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The Amazon is the world’s largest and most biodiverse tropical rainforest – but could deforestation push it past a tipping point? Scientists believe that could happen within the next 20 years, with dire consequences for the climate. Here’s all you need to know about Amazon dieback, plus the Gulf Stream, the West Antarctic ice sheet and other climate tipping points.

This session will be in English

If the Amazon rainforest were a country, it would be the seventh largest in the world.
Spanning nine countries across South America, it covers around 5.5 million square kilometers, which makes it almost twice the size of India.

The Amazon is home to at least 10% of all known species on the entire planet, along with around 30 million people from more than 350 different ethnic groups.

It’s also one of our most important defenses against climate change, storing up to 200 billion tons of carbon, which is roughly five years’ worth of global carbon emissions from the burning of fossil fuels.

But humans are slowly tearing it down. About 18% of the Amazon has already been destroyed, and many scientists now believe we could soon reach a tipping point where the Amazon starts to dry up and can no longer function as a rainforest.

Chapter: Amazon dieback (0:48)

So, what would that mean for its people, for wildlife – and for the rest of the world?

As the word suggests, a rainforest is a mostly evergreen forest that gets large amounts of rainfall. Rainforests are found on every continent except Antarctica, from the Amazon in South America to the Congo Rainforest in Central Africa to the various rainforests of Southeast Asia and New Guinea. They’re home to more than half of the world’s known species – despite covering just 6% of the Earth’s surface.

There are two types of rainforest: temperate and tropical, and the world’s largest tropical rainforest is – you guessed it – the Amazon.

Now, the way that rainforests can sustain themselves is that they’re often self-watering. Tropical rainforests are hot and humid, and that humidity leads to frequent and intense rainfall. Plants soak up that rainwater and then release it back into the atmosphere through evaporation and transpiration. So, rainfall and humidity help sustain the rainforest, but at the same time, the rainforest also helps keep the climate rainy and humid. In fact, rainforests can generate up to 75% of their own rain.

But what happens when a rainforest gets cut down? Deforestation is one of the biggest threats to rainforests across the globe. The Amazon has already lost 18% of its tree cover, and it’s losing an extra 1% roughly every three years. Some of the main drivers include logging, ranching, mining and agriculture.

Scientists fear that the Amazon could soon hit a tipping point where it starts to permanently dry out. Here’s how that would work: fewer trees means less transpiration, and once tree cover drops below a certain point, the rainforest will no longer produce enough rainfall to sustain itself. So, in as little as 15 to 20 years’ time, we could see large parts of the Amazon start to turn from a rainforest into a much drier ecosystem with far fewer trees, in a process known as ‘dieback.’

That would release huge amounts of carbon dioxide into the atmosphere, contributing to climate change. It would also mean the loss of biodiversity and ecosystem services like pollination, clean water and recreation, which would have drastic consequences even thousands of kilometers away.

That’s because the trees in the Amazon provide moisture that gets carried by the wind across the Americas and perhaps even as far as the midwestern US. So, the collapse of the Amazon could lead to more frequent droughts and lower crop yields across the Western Hemisphere.
These changes could cause trillions of dollars in damage to the global economy – and they could take centuries to reverse, if they can be reversed at all.

Chapter: What are climate tipping points? (3:24)

Amazon dieback is a prime example of what’s known as a climate tipping point: a small shift in the climate system that could have drastic long-term consequences for the entire planet.

You can think of it like a game of Jenga: as the Earth’s temperature rises, we’re removing blocks from the tower and placing them on top, causing it to become increasingly unstable, until eventually, the tower can no longer support itself and collapses.

In 2019, a team of climate scientists identified nine key tipping points in the climate system, from Amazon dieback to the loss of coral reefs to the melting of Arctic permafrost. Crossing any one of these thresholds would most likely cause climate change to accelerate rapidly and irreversibly, and could even trigger other tipping points, causing a domino effect.

Chapter: Greenland and Antarctic ice sheets (4:12)

Unfortunately, there’s one tipping point that we’re very close to crossing. Around 99% of the world’s freshwater is currently stored in the ice sheets of Greenland and Antarctica.

Remember that one of the biggest threats from climate change is rising sea levels, which is mainly due to the melting of land and sea ice near the poles. The western part of Antarctica holds enough ice to raise global sea levels by 3.3 m, or almost 11 feet.

There are two glaciers in West Antarctica that have scientists particularly worried: Thwaites Glacier, the widest glacier on Earth, covering an area the size of Great Britain, and right next to it, Pine Island Glacier, which is only slightly smaller.

Both of these glaciers have what are known as ice shelves, which are large walls of ice that float on top of the ocean and act as a ‘cork in the bottle’ to hold the rest of the ice sheet in place. But as the Earth gets warmer, the front of the ice shelves is breaking apart, causing ice to flow into the ocean faster than ever.

On top of that, both Thwaites and Pine Island lie on bedrock that’s below sea level. As warm water undercuts the ice shelves, it’s causing the glaciers to melt from below. That pushes back the point where the edge of the glacier sits on the bedrock, which causes even more ice to be lifted off the land and float on the water. That’s causing global sea levels to rise, just like adding ice cubes to a drink.

Since 2017, Pine Island has receded by about 4.5 km each year, almost double the rate in 1992. If both of these glaciers were to melt, they could raise global sea levels by more than a meter.

While we don’t know where these tipping points lie, some climate scientists believe they could be triggered if global temperatures rise by as little as 1.5 degrees. Others say Thwaites has already passed a tipping point and will collapse eventually.

Either way, the only way to prevent a total collapse of West Antarctica is to reduce our greenhouse gas emissions as quickly as possible to keep global warming to a minimum.

Chapter: The Gulf Stream (6:13)

Have you ever wondered why winters in Western Europe are so much warmer than in eastern North America? For instance, Lisbon is at almost the exact same latitude as Washington, DC, but its mean temperature in January is about 11 degrees Celsius, compared to just 3 degrees in Washington.

The answer has a lot to do with ocean currents in the Atlantic. One of these currents is known as the Gulf Stream, which carries warm water from the Gulf of Mexico up north across the Atlantic and towards Europe, where it releases heat into the atmosphere.

The Gulf Stream is part of a larger system known as the Atlantic Meridional Overturning Circulation, or AMOC. AMOC works like a global ocean conveyor belt that helps distribute heat and energy around the world. As water moves north, it becomes colder and saltier due to evaporation, making it denser. That cold water sinks deeper into the ocean near Iceland and Greenland and travels back south all the way to Antarctica and into the Indian and Pacific Oceans, where it rises back up to the surface. Eventually, it makes its way back to the Atlantic to complete a full cycle that can take roughly 1,000 years.

But scientists have discovered that the system is slowing down. It’s already about 15% weaker than it was in the 1950s, and it’s now at its weakest point in at least 1,600 years.

Climate change is making the problem worse. Remember that cold and salty water is denser, which causes it to sink, while warmer and less salty water rises. As the Earth gets warmer, glaciers are melting and rainfall is increasing. The more it rains, and the more glaciers melt, the less salty the ocean becomes. That makes the water less able to sink, and so the entire circulation slows down.

So now, the big question is: could it cross a tipping point where it shuts down entirely, just like in the Hollywood film The Day After Tomorrow?

Okay, so the movie is based on some pretty sketchy science, and the world isn’t really heading towards another ice age. But we would probably still see colder weather across much of the northern hemisphere, more frequent winter storms in Europe, drastic changes to rainfall patterns, and a half-meter sea level rise, in addition to all other impacts of climate change.

And once again, scientists aren’t sure where the tipping point lies, but we’re already seeing early signs that AMOC could be on the brink of collapse. Still, we’ve got a good chance of preventing it – if we can keep global warming below 2 degrees Celsius.

Chapter: Why we need climate action (8:44)

So, there’s a common thread running through these climate tipping points: we need to act now to stop runaway climate change. According to the UN, the world is on track for over 3 degrees of warming by the year 2100 – and world leaders are doing nowhere near enough to prevent that from happening.

In the Brazilian Amazon, deforestation has soared under President Jair Bolsonaro, who has weakened environmental protections and encouraged development in the Amazon since taking office in 2019. Brazil’s deforestation rates are now at their highest in 12 years.

And despite new climate targets from rich countries like the US, Canada, Japan and the UK, they’re still only enough to limit global warming to 2.4 degrees – not to mention there hasn’t been much in the way of actual policies to achieve those targets.

But the climate crisis won’t wait. Heatwaves are going to become much more likely in the coming decades as the planet gets hotter. And as wildfires, floods, hurricanes and other climate disasters grow more frequent and more intense, the onus is on us to act before it’s too late.

So, that’s it for today’s episode. Let us know in the comments what you think it would take to keep global warming below 2 degrees. And if you enjoyed this video, please remember to smash that like button and subscribe to our channel for more content from Landscape TV. Thank you for watching, and we’ll see you next time.