It Every day begins at night. As the light fades, billions of zooplankton, crustaceans and other marine life rise to the ocean's surface to feed on microscopic algae, returning to the depths at sunrise. The waste from this frenzy – the largest migration of Earth's species – removes millions of tonnes of carbon from the atmosphere and onto the ocean floor every year.
This activity is one of thousands of natural processes that regulate Earth's climate. Together, the planet's oceans, forests, soils and other natural carbon sinks absorb about Half of human emissions.
But scientists are increasingly concerned that as the Earth warms, those critical processes are breaking down.
In 2023, the hottest year on record, preliminary findings by an international team of researchers show that the amount of carbon sequestered by land has temporarily declined. The bottom line is that forests, plants and soil – as a net category – absorb almost no carbon.
There are also warning signs in the sea. Greenland's glaciers and Arctic ice are melting faster than expected, disrupting the Gulf Stream ocean current and slowing the rate at which the oceans absorb carbon. For algae-eating zooplankton, melting sea ice exposes them to more sunlight – a change scientists say disrupts the vertical migration that stores carbon on the sea floor, keeping them at depth longer.
“We see cracks in the resilience of Earth's systems. We are seeing massive cracks in the land – terrestrial ecosystems are losing their carbon storage and carbon absorption capacity, but the oceans are also showing signs of instability,” Johan Rockström, Director of Climate Impact Research at Potsdam, said at an event in the Neue. September is York Climate Week.
“Nature has so far balanced our abuse. It is coming to an end,” he said.
The breakdown of the land carbon sink in 2023 may be temporary: without the stress of drought or wildfires, the land will resume absorbing carbon. But it demonstrates the fragility of these ecosystems with massive implications for the climate crisis.
Achieving net zero is inherently impossible. In the absence of technology to remove large-scale atmospheric carbon, Earth's vast forests, grasslands, peat bogs and oceans are the only way to absorb human carbon pollution. A record 37.4 billion tonnes in 2023.
At least 118 countries rely on land to meet national climate targets. But rising temperatures, increased extreme weather and drought are pushing ecosystems into uncharted territory.
The rapid land sink decline seen in 2023 is not factored into most climate models. If this continues, it raises the possibility of faster global warming than those models predict.
'We've become silent – we can't see the crisis'
For the past 12,000 years, Earth's climate has been in delicate balance. Its stable weather patterns allowed the development of modern agriculture, which now supports more than 8 billion people.
As human emissions increased, so did the amount absorbed by nature: more carbon dioxide meant faster plant growth. Saves more carbon. But this balance is starting to shift, driven by rising temperatures.
Photo: G Kuni/Getty
“This stressful planet is silently helping us, allowing us to sweep our debt under the rug thanks to biodiversity,” says Rockstrom. “We've been pushed into a comfort zone – we can't really see the crisis.”
Only one major tropical rainforest – the Congo Basin – is a strong carbon sink that removes more than it releases into the atmosphere. Exacerbated by El Niño weather patterns, deforestation and global warming, the Amazon basin is experiencing record drought, with rivers at all-time lows. The expansion of agriculture has turned tropical rainforests in Southeast Asia into a net source of emissions in recent years.
Emissions from soil – the second largest active carbon store after the oceans – are expected to increase by 40% by the end of the century if they continue at current rates, as soils dry out and microbes break them down faster.
Tim Lenton, Professor of Climate Change and Earth System Sciences at the University of Exeter, says: “Just as we are in climate, we are seeing some surprising responses in the biosphere that are not predicted.
“You have to ask the question: To what extent can we trust them as carbon sinks or carbon stores?” He says.
A paper published in July found that while the total amount of carbon absorbed by forests remained constant between 1990 and 2019, it varied significantly by region. Boreal forests – home to a third of all carbon found on land across Russia, Scandinavia, Canada and Alaska – have seen a sharp decline in the amount of carbon they absorb. More than a third are related to climate crisis-related beetle outbreaks, fires and tree removal.
Decreasing drought conditions in the Amazon and parts of the tropics have contributed to the collapse of the land sink by 2023 – causing a spike in atmospheric carbon levels.
“CO Accumulation in 20232 is very high in the atmosphere and this translates into very, very low absorption by the terrestrial biosphere,” says researcher Philippe Cias of the French Climate and Environmental Sciences Laboratory. Latest paper.
“More than half of the Northern Hemisphere is CO2 We have seen a declining trend in absorption for eight years,” he says. “There's no good reason to believe it will bounce back.”
Oceans – Nature's largest CO sink2 – Has soaked up 90% of warming from fossil fuels in recent decades, increasing ocean temperatures. Studies have also found signs that this is weakening the ocean carbon sink.
'No model has factored this in'
The flow of carbon through land and ocean is one of the least understood areas of climate science, researchers say. Although human emissions are relatively simple to measure, the sheer number and complexity of processes in the natural world represent important gaps in our understanding.
Satellite technology has improved monitoring of forests, peatlands, permafrost and ocean cycles, but estimates and forecasts in international reports often have large margins of error. This makes it difficult to predict how the world's natural carbon sinks will behave in the future – and many models do not factor in the sudden breakdown of many ecosystems.
“Overall, the models agree that both land subsidence and ocean subsidence will decrease in the future as a result of climate change. But the question is how quickly that will happen. “Models tend to show this slowing over the next 100 years,” says Professor Andrew Watson, head of the University of Exeter's Ocean and Atmospheric Sciences Group.
“It can happen very quickly,” he says. “Climate scientists [are] Worrying about climate change is not because of what is in the models, but because of the knowledge that the models are missing some things.”
Many recent Earth system models used by scientists factor in some of the effects of global warming on nature, such as the shrinking of the Amazon or slowing ocean currents. But scientists say the events that have become major sources of emissions in recent years are not linked.
“None of these models factor in losses as extreme as last year's wildfires in Canada, which account for six months of US fossil fuel emissions. Two years ago, we wrote a paper that found Siberia lost the same amount of carbon,” says Sias.
“Another process missing from climate models is the basic fact that trees die from drought. This is observed and none of the samples representative of the land sink have drought-induced mortality,” he says. “The fact that the models don't have these factors makes them more promising.”
'What happens when natural sinks stop working?'
The consequences for climate goals are stark. Even by weakening nature's ability to absorb carbon by a small amount, the world would need to cut greenhouse gas emissions very deeply to reach net zero. The weakness of land sinks – which until now has been regional – has also had the effect of nullifying countries' progress towards decarbonisation and climate goals, which is proving a struggle for many countries.
In Australia, large soil carbon losses from extreme heat and drought in the vast interior known as rangelands will push it short of its climate targets if emissions continue to rise. A study this year found that In Europe, France, Germany, the Czech Republic and Sweden have all experienced significant declines in the amount of carbon absorbed by land, driven by climate-related bark beetle outbreaks, drought and increased tree mortality.
Finland, which has one of the most ambitious carbon neutrality targets among the developed world, has seen the largest land sink in recent years – meaning that while all industries have cut their emissions by 43%, the country's total emissions have remained unchanged.
So far, these changes have been regional. Some countries, such as China and the United States, have yet to experience such a decline.
“The issue of natural sinks has never been properly thought through in the political and governmental spheres. It is assumed that natural sinks are always with us. The truth is, we don't understand them and we don't think they will always be with us. What if the climate changes and the natural sinks they once relied on stop working? Watson says.
In recent years, many estimates have been published on how the world could increase the amount of carbon absorbed by its forests and natural ecosystems. But many researchers say the real challenge is to protect the carbon sinks and stores we already have by stopping deforestation, reducing emissions and ensuring we stay as healthy as possible.
“We should not depend on natural forests to work. We have to tackle a really big problem: fossil fuel emissions in all sectors,” says Professor Pierre Friedlingstein of the University of Exeter, who oversees the annual. Global Carbon Budget Calculations.
“We cannot assume that we have forests and that the forest will remove some CO2Because it's not going to work in the long run.
