Last week, hundreds of scientists, policymakers and journalists flocked to the University of Exeter to attend an international conference on “tipping points”.
The conference saw experts discussing the dangers of a range of Earth system tipping points, including the dieback of the Amazon, the melting of the Greenland ice sheet and the shutdown of the Atlantic Meridional Overturning Circulation (AMOC).
Attendees also explored “positive tipping points” – large-scale, self-propelling social changes that would reduce the impact of humans on the climate.
(For more on the key talking points, new research and ideas that emerged from the four-day event, see Carbon Brief’s full write-up of the event.)
On the sidelines of the conference, Carbon Brief asked a wide range of delegates which tipping point concerns them the most.
These are their responses, first as sample quotes, then, below, in full:
- Prof Gabi Hegerl: “I am particularly worried about tipping points that involve the biosphere and humans due to breaching thresholds for heat or drought that then ripple into food availability, livelihood and ecosystems.”
- Prof Carlos Nobre: “The Amazon is a very serious tipping point, because [dieback] could release around 250bn tonnes of CO2 by 2100 – which will make it impossible to [limit global warming] at 1.5C.”
- Gaia Vince: “I would say that we have already passed the tipping point for coral reef ecosystems…As a scuba diver, I find it a tragedy because I love coral reef ecosystems, but it’s also a tragedy for human systems.”
- Dr Andrew Hartley: “The tipping point I’m most concerned about is Amazon forest dieback…because of the significance of the carbon cycle and the feedback to the global climate. Also [due to] the effects that Amazon tipping has on food security, both locally and globally.”
- Prof Tim Lenton: “The Atlantic Meridional Overturning Circulation, or AMOC, for sure. The consequences of crashing that would be devastating globally – and also for where I live in the UK.”
- Prof Peter Cox: “The one that I’ve worked on most and worries me most at the moment is Amazon dieback. And that’s because we’ve got two things, two stressors, going on at once that push it in the wrong direction. Climate change is one, deforestation is another.”
- Prof Johan Rockström: “The tipping element that worries me most is coral reef systems, for the simple reason that the scientific uncertainty range is very limited.”
- Dr Patricia Pinho: “For me, it is the Amazon…I think it’s going to be a really profound, irreversible change that will affect the global population in the most dramatic way.”
- Prof Ricarda Winkelmann: “I’m mostly concerned about the Greenland and West Antarctic ice sheets. This is because we know that, even at lower warming levels, they are already at risk of transgressing tipping points in certain regions.”
- Dr Nico Wunderling: “The tipping element that worries me most is the Amazon rainforest. This is because the Amazon rainforest is not only threatened by climate change, but also by deforestation at the same time.”
- Dr Rebecca Shaw: “The coral reef tipping point…It signals the end of the most colourful and biodiverse ecosystem which supports the nutrition and livelihoods of over one billion people.”
- Dr David Obura: “The ice [tipping elements] – because they are the first ones to go that have cascading impacts on other tipping elements.”
- Dr David Armstrong McKay: “The Amazon is actually probably closer to a deforestation-induced tipping point than to a climate change-induced tipping point. So, I actually think that could be potentially in the offing sooner than we would like.”
- Kate Raworth: “The tipping point that I fear we will fail to cross is [the social tipping point] around transforming our mindsets.”
Chair in climate system science in the school of geosciences at the University of Edinburgh
I am worried about all of them, but for the immediate future, I am particularly worried about tipping points that involve the biosphere and humans due to breaching thresholds for heat or drought that then ripple into food availability, livelihood and ecosystems. The Earth system tipping points will do that too, but maybe a little bit later. Examples [of this] are the coral diebacks triggered by marine heatwaves, forest change and fires, and droughts threatening livelihoods and putting people on the move.
I did a research project on the US Dust Bowl and the trigger [for that event] was drought causing vegetation and crop dieback, [which led to] extreme heat and dust storms in response – and migration, as memorialised in [the 1939 John Steinbeck novel] The Grapes of Wrath. And, now with warming, all droughts get supercharged.
Prof Carlos Nobre
Scientist and meteorologist who spearheaded the multi-disciplinary, multinational large-scale biosphere-atmosphere experiment in Amazonia
The Amazon is a very serious tipping point, because [dieback] could release around 250bn tonnes of CO2 by 2100 – which will make it impossible to [limit global warming] at 1.5C. We could also lose the largest [host to] biodiversity on the planet, which would induce a tremendous, large number of epidemics and several pandemics. Also, of course, the Amazon forest controls aspects of the global climate. In South America, the climate is entirely controlled by the Amazon forest.
I’m most worried about Amazon [dieback] because I have worked on it for 40 years. But the other tipping points deeply concern me. The melting of the permafrost will release more than 200bn tonnes [of greenhouse gases], mostly methane. Ice sheet melt in Greenland is a very serious tipping point because it could raise sea level rise by three metres in 200 years. The melting of Greenland has already started. Species extinction is also very serious.
One thing that was not much talked about [at this conference] is that when the ocean heats up, particularly the Arctic Ocean, then a tremendous amount of methane is released. And if that happens – if the Arctic Ocean warms up by 3-4C – the amount of methane that would be released could see [air] temperatures reach 8-10C [above pre-industrial levels]. At 8-10C, the only inhabitable places for us humans will be the top of the Alps, the Andes and the north and south poles. The rest of the planet would be uninhabitable.
Gaia Vince
Science writer and broadcaster
I would say that we have already passed the tipping point for coral reef ecosystems, for example. That really is a tragedy. As a scuba diver, I find it a tragedy because I love coral reef ecosystems, but it’s also a tragedy for human systems. They are the nursery for our fisheries. And, of course, they’re not just fisheries – they are a valid ecosystem and a biodiversity hotspot. This will have untold consequences and cascading impacts for other parts of the ecosystem, for example, the cycling of nutrients and coral reefs are really important to stop coastal erosion. And they actually provide sand, the lovely white sand that people go on holiday for Bucha.
Dr Andrew Hartley
Climate impacts scientist at the Met Office Hadley Centre
The tipping point I’m most concerned about is Amazon forest dieback and reduction in the function of the Amazon forest, because of the significance of the carbon cycle and the feedback to the global climate. Also [due to] the effects that Amazon tipping has on food security, both locally and globally, because of [the Amazon’s] contribution to major commodity markets, such as soybean and maize.
This might interact with climate change in the future to lead to more severe events, particularly in populated areas of Brazil. If an Amazon tipping point were to occur, it might lead to more severe events on the coast of Brazil which would affect a much larger population. There are negative impacts across the forest from the drying of the forest, for example for the Indigenous communities, but also globally.
Prof Tim Lenton
Founding director of the Global Systems Institute and chair in climate change and Earth system science at the University of Exeter
The Atlantic Meridional Overtoning Circulation, or AMOC, for sure. The consequences of crashing that would be devastating globally – and also for where I live in the UK. By our own calculation, we could have less than half the viable area for growing a couple of major staple crops, wheat and maize worldwide. We would have a widespread water crisis. We could have collapses of the monsoons in West Africa and India that would displace hundreds of millions of people. It is hard to see that as anything other than a catastrophe.
Prof Peter Cox
Professor of climate system dynamics in mathematics and director of the Global Systems Institute at the University of Exeter
The one that I have worked on most and worries me most at the moment is Amazon dieback. And that’s because we’ve got two things, two stressors going on at once that push it in the wrong direction. Climate change is one, deforestation is another. You can imagine crossing the boundary in various ways – but, if you push diagonally, you get there quicker.
If I had spoken to you 25 years ago, I would have said I’m really worried about [Amazon dieback]. Then I went through a phase of thinking that the models have overdone it. And now I’m thinking the models that don’t include land-use change are underdoing it. So, I’m more concerned about that one.
There are others as well, but that is the one that is also quite fast. The other [tipping points] we worry about, we’re worried about a long-term commitment. It takes a while for the AMOC to shut down, it really does. It takes a while for the Greenland ice sheet to melt. We’ve done work that suggests you can overshoot even a little bit for these slow systems. The Amazon forest is a decadal dieback, especially if it is fire driven.
Prof Johan Rockström
Director of the Potsdam Institute for Climate Impact Research (PIK) and professor in Earth system science at the University of Potsdam
There is not a simple answer to this – there is a two-part answer.
The tipping element that worries me most is coral reef systems, for the simple reason that the scientific uncertainty range is very limited. We have, unfortunately, ample evidence that at 1.5C we’re very likely to knock over, potentially, the entire tropical coral reef system on Earth. [This threatens] the livelihoods of 400 million people and a fundamental nursing ground for the whole ocean food web. So that is one deep concern. It is the canary in the coal mine – the first kid on the block to fall over. We’re so close.
The second one is AMOC – the whole overturning of heat in the Atlantic, which connects the entire ocean system. Not only is the latest science showing that we are going from low likelihood to uncomfortably high likelihood, but we also know – with very little uncertainty – that this would cause a catastrophic impact across the entire world, and it would go fast. So the AMOC, I would argue, is today the most important scientific message to the world. If you want a really hard-hitting reason to act at a level of planetary emergency, it is the AMOC. That is the second one.
From a planetary boundary perspective, it is important to recognise that – on climate science grounds – the Amazon basin is not at risk of tipping until 3-5C of warming. But as soon as you factor in loss of biodiversity, deforestation and changes in hydrology – then the temperature risk goes down to between 1.5-2C. So suddenly – when taking a more integrated [assessment] approach – the conclusion is that it is also very close to a tipping point.
Dr Patricia Pinho
Deputy science director at the Amazon Environmental Research Institute (IPAM)
For me, it is the Amazon. When we think of the planetary crisis, we think about the Amazon and all the regulating climate services it provides. This is not only regionally, but we know it’s a global “climate good”, if you will. But it is highly sensitive to land-use change and increasing temperature. So, if we transition to a point of no return – Amazon dieback – and transforming or transitioning to another ecosystem, the function of the forest will not be doing what it has been doing for the past millennium and so on. And then we cannot revert this loss. I think it is going to be a really profound, irreversible change that will affect the global population in the most dramatic way.
Of course, we have the people on the front line that I’m working with – Indigenous people, traditional population – that are safeguarding this resource, but they are also at the front line of climate risks and the impacts that we already observe. If we miss this opportunity of really reverting from increasing greenhouse emissions and increasing temperature, we’re going to miss the window of opportunity to really protect the region, protect the ecosystem and the forest for the global society.
Prof Ricarda Winkelmann
Founding director of the Max Planck Institute of Geoanthropology and professor of climate system analysis at PIK and the University of Potsdam
So I am thinking about this from a risk perspective – so both the likelihood as well as the impacts – and I think the answer depends on that. Because when it comes to the likelihood and the particular threshold – and we know about those – I’m mostly concerned about the Greenland and the West Antarctic ice sheets. This is because we know that, even at lower warming levels, they’re already at risk of transgressing tipping points in certain regions.
But when it comes to the impacts and also the timescales over which those play out, there are other tipping elements that worry me most. In particular, regional tipping elements. So if we think of the mountain glaciers, for instance, these impacts are already experienced right now and several mountain glaciers are undergoing these accelerated changes. And so thinking about the timescales when it comes to the impacts is also incredibly important.
Dr Nico Wunderling
Junior professor at the Center for Critical Computational Studies at Goethe University Frankfurt and researcher at the Potsdam Institute for Climate Impact Research.
The tipping element that worries me most is the Amazon rainforest. This is because the Amazon rainforest is not only threatened by climate change, but also by deforestation at the same time. So that means that the critical threshold from climate change alone, at around 3-4C of global warming, can come down to 1.5-2C. Climate change and deforestation basically go hand-in-hand to lower the [Amazon’s tipping] threshold because of this double threat.
Dr Rebecca Shaw
Chief scientist and senior vice-president at WWF
The coral reef tipping point – it comes first because of warming surface waters, and then the outcome is sealed by ocean acidification. It signals the end of the most colourful and biodiverse ecosystem which supports the nutrition and livelihoods of over one billion people and has captured the imagination of more people than any other through the characters like Nemo the clownfish, SpongeBob SquarePants, and, of course, Frank the coral [a character from an educational YouTube video].
If humanity is not motivated to act in the face of the loss of coral reefs, is there hope that we will act in time to prevent the Amazon and glacier tipping points?
Dr David Obura
Chair of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services and founding director of CORDIO East Africa
The ice [tipping elements] – because they are the first ones to go that have cascading impacts on other tipping elements. When [ice masses] reduce, we lose their albedo, waters heat up more [and] the AMOC can collapse. That has the biggest impact across the planetary system, including the Amazon.
My own [research], of course, is coral reefs. So, in a way, the coral reef tipping point does concern me the most. [But] it doesn’t have cascading impacts on other tipping elements. It does on people, in socioeconomic terms – but not on other system elements. So, in a sense, it is the least worrying one.
Dr David Armstrong McKay
Lecturer in geography, climate change and society in the school of global studies at the University of Sussex and lead author on an influential tipping points assessment, published in Science in 2022
One of the tipping systems that concerns me the most is Amazon rainforest dieback. Because even though we assessed it a few years ago as having a warming threshold that’s a bit higher than what we might be seeing – we’ve thought it is maybe at a best estimate of 3.5C – there’s also deforestation as well. The Amazon is actually probably closer to a deforestation-induced tipping point than to a climate change-induced tipping point. So I actually think that could be potentially in the offing sooner than we would like. That would have huge impacts for biodiversity, for South America as a whole, by shifting rainfall patterns, which would really affect a lot of people for agriculture or ecosystems. Also, the Amazon as an ecosystem is so incredibly biodiverse and amazing in itself, it would be a tragedy to lose it.
Kate Raworth
Senior visiting research associate and lecturer at the University of Oxford’s Environmental Change Institute and co-founder and conceptual lead of Doughnut Economics Action Lab
The tipping point that I fear we will fail to cross is [the social tipping point] around transforming our mindsets. We need to move from the extractive, degenerative economy towards a regenerative one. This all starts within our head and it underlies everything.
[A failure to do this] is what is driving us towards all these [Earth system tipping points].
The post Experts: Which climate tipping point is the most concerning? appeared first on Carbon Brief.
Experts: Which climate tipping point is the most concerning?
Drought and heatwaves occurring together – known as “compound” events – have “surged” across the world since the early 2000s, a new study shows.
Compound drought and heat events (CDHEs) can have devastating effects, creating the ideal conditions for intense wildfires, such as Australia’s “Black Summer” of 2019-20 where bushfires burned 24m hectares and killed 33 people.
The research, published in Science Advances, finds that the increase in CDHEs is predominantly being driven by events that start with a heatwave.
The global area affected by such “heatwave-led” compound events has more than doubled between 1980-2001 and 2002-23, the study says.
The rapid increase in these events over the last 23 years cannot be explained solely by global warming, the authors note.
Since the late 1990s, feedbacks between the land and the atmosphere have become stronger, making heatwaves more likely to trigger drought conditions, they explain.
One of the study authors tells Carbon Brief that societies must pay greater attention to compound events, which can “cause severe impacts on ecosystems, agriculture and society”.
Compound events
CDHEs are extreme weather events where drought and heatwave conditions occur simultaneously – or shortly after each other – in the same region.
These events are often triggered by large-scale weather patterns, such as “blocking” highs, which can produce “prolonged” hot and dry conditions, according to the study.
Prof Sang-Wook Yeh is one of the study authors and a professor at the Ewha Womans University in South Korea. He tells Carbon Brief:
“When heatwaves and droughts occur together, the two hazards reinforce each other through land-atmosphere interactions. This amplifies surface heating and soil moisture deficits, making compound events more intense and damaging than single hazards.”
CDHEs can begin with either a heatwave or a drought.
The sequence of these extremes is important, the study says, as they have different drivers and impacts.
For example, in a CDHE where the heatwave was the precursor, increased direct sunshine causes more moisture loss from soils and plants, leading to a drought.
Conversely, in an event where the drought was the precursor, the lack of soil moisture means that less of the sun’s energy goes into evaporation and more goes into warming the Earth’s surface. This produces favourable conditions for heatwaves.
The study shows that the majority of CDHEs globally start out as a drought.
In recent years, there has been increasing focus on these events due to the devastating impact they have on agriculture, ecosystems and public health.
In Russia in the summer of 2010, a compound drought-heatwave event – and the associated wildfires – caused the death of nearly 55,000 people, the study notes.
The record-breaking Pacific north-west “heat dome” in 2021 triggered extreme drought conditions that caused “significant declines” in wheat yields, as well as in barley, canola and fruit production in British Columbia and Alberta, Canada, says the study.
Increasing events
To assess how CDHEs are changing, the researchers use daily reanalysis data to identify droughts and heatwaves events. (Reanalysis data combines past observations with climate models to create a historical climate record.) Then, using an algorithm, they analyse how these events overlap in both time and space.
The study covers the period from 1980 to 2023 and the world’s land surface, excluding polar regions where CDHEs are rare.
The research finds that the area of land affected by CDHEs has “increased substantially” since the early 2000s.
Heatwave-led events have been the main contributor to this increase, the study says, with their spatial extent rising 110% between 1980-2001 and 2002-23, compared to a 59% increase for drought-led events.
The map below shows the global distribution of CDHEs over 1980-2023. The charts show the percentage of the land surface affected by a heatwave-led CDHE (red) or a drought-led CDHE (yellow) in a given year (left) and relative increase in each CDHE type (right).
The study finds that CDHEs have occurred most frequently in northern South America, the southern US, eastern Europe, central Africa and south Asia.
Threshold passed
The authors explain that the increase in heatwave-led CDHEs is related to rising global temperatures, but that this does not tell the whole story.
In the earlier 22-year period of 1980-2001, the study finds that the spatial extent of heatwave-led CDHEs rises by 1.6% per 1C of global temperature rise. For the more-recent period of 2022-23, this increases “nearly eightfold” to 13.1%.
The change suggests that the rapid increase in the heatwave-led CDHEs occurred after the global average temperature “surpasse[d] a certain temperature threshold”, the paper says.
This threshold is an absolute global average temperature of 14.3C, the authors estimate (based on an 11-year average), which the world passed around the year 2000.
Investigating the recent surge in heatwave-leading CDHEs further, the researchers find a “regime shift” in land-atmosphere dynamics “toward a persistently intensified state after the late 1990s”.
In other words, the way that drier soils drive higher surface temperatures, and vice versa, is becoming stronger, resulting in more heatwave-led compound events.
Daily data
The research has some advantages over other previous studies, Yeh says. For instance, the new work uses daily estimations of CDHEs, compared to monthly data used in past research. This is “important for capturing the detailed occurrence” of these events, says Yeh.
He adds that another advantage of their study is that it distinguishes the sequence of droughts and heatwaves, which allows them to “better understand the differences” in the characteristics of CDHEs.
Dr Meryem Tanarhte is a climate scientist at the University Hassan II in Morocco, and Dr Ruth Cerezo Mota is a climatologist and a researcher at the National Autonomous University of Mexico. Both scientists, who were not involved in the study, agree that the daily estimations give a clearer picture of how CDHEs are changing.
Cerezo-Mota adds that another major contribution of the study is its global focus. She tells Carbon Brief that in some regions, such as Mexico and Africa, there is a lack of studies on CDHEs:
“Not because the events do not occur, but perhaps because [these regions] do not have all the data or the expertise to do so.”
However, she notes that the reanalysis data used by the study does have limitations with how it represents rainfall in some parts of the world.
Compound impacts
The study notes that if CDHEs continue to intensify – particularly events where heatwaves are the precursors – they could drive declining crop productivity, increased wildfire frequency and severe public health crises.
These impacts could be “much more rapid and severe as global warming continues”, Yeh tells Carbon Brief.
Tanarhte notes that these events can be forecasted up to 10 days ahead in many regions. Furthermore, she says, the strongest impacts can be prevented “through preparedness and adaptation”, including through “water management for agriculture, heatwave mitigation measures and wildfire mitigation”.
The study recommends reassessing current risk management strategies for these compound events. It also suggests incorporating the sequences of drought and heatwaves into compound event analysis frameworks “to enhance climate risk management”.
Cerezo-Mota says that it is clear that the world needs to be prepared for the increased occurrence of these events. She tells Carbon Brief:
“These [risk assessments and strategies] need to be carried out at the local level to understand the complexities of each region.”