As much as half of the Amazon will face several “unprecedented” stressors that could push the forest towards a major tipping point by 2050, new research finds.
The largest rainforest in the world is already under pressure from climate change, deforestation, biodiversity loss and extreme weather.
Researchers analysed data on five key drivers of water stress in the Amazon and looked at how these pressures could lead to “local, regional or even biome-wide forest collapse”.
The new study, published in Nature, finds that by 2050, between 10 and 47% of the Amazon forest will be exposed to “compounding disturbances” that “may trigger unexpected ecosystem transitions”. This could result in large swathes of lush rainforest shifting to dry savannah.
One author of the study tells Carbon Brief that this prospect by mid-century is “very scary”.
The study notes that the complexity of the Amazon “adds uncertainty about future dynamics” and that there are still “opportunities for action”.
The findings highlight the likelihood that “climate change will continue to affect the forest in very unpredictable ways”, a scientist not involved in the study says.
Amazon pressures
The Amazon forest stores a huge amount of carbon and houses at least 10% of the world’s biodiversity. It faces an uncertain future largely due to the effects of deforestation and climate change.
Last year, the Amazon river basin experienced an “exceptional drought” that was 30 times more likely to occur due to climate change, a rapid attribution study found.
Around 20% of the Amazon has already been deforested and a further 6% is “highly degraded”.
According to several studies, the Brazilian section of the Amazon is now an overall net “source” of carbon, rather than a “sink”, due to a number of factors including deforestation.
Scientists have long warned that climate change and human-driven deforestation could push the Amazon rainforest past a “tipping point” – a threshold that, if crossed, would see the “dieback” of large amounts of dense Amazon rainforest and a shift into permanent, dry savannah.
This would be characterised by a mixed tree and grassland system with an open canopy that allows the soil to become much hotter and drier.
Previous studies suggest that the Amazon could be pushed beyond this tipping point if forest loss exceeds 40%. Other research published last October found that recent drying over the Amazon could be the “first warning signal” that the rainforest is approaching a tipping point.
The new study examines five key drivers of water stress in the Amazon – global warming, annual rainfall, rainfall seasonality intensity, dry season length and accumulated deforestation – to estimate the critical limits of these issues for the Amazon.
The researchers use existing evidence from palaeorecords, observational data and modelling studies. For example, they find that rainfall levels below 1,000mm each year could result in “forests becom[ing] rare and unstable”.
For floodplain ecosystems, this critical threshold was estimated at 1,500mm per year. This implies that “floodplain forests may be the first to collapse in a drier future”, the study says.
Based on this analysis, the researchers estimate that these drivers could, in combination, potentially lead to a large-scale Amazon tipping point by 2050.
Dr Bernardo Flores, the lead author of the study and a researcher at the Federal University of Santa Catarina, Brazil, says the study aims to show the effects of these combined pressures. He tells Carbon Brief:
“It is surprising how the combination of stressors and disturbances are already affecting parts of the central Amazon… [which] can already transition into different ecosystems.
“Then, when you put everything together, the possibility that by 2050 we could cross this tipping point, a large-scale tipping point, is very scary and I didn’t really think it could be so soon.”
Ecosystem transitions
The findings highlight how the combination of different disturbances – such as intensified droughts and fires – could trigger “unexpected ecosystem transitions even in remote and central parts” of the Amazon.
Flores says that most of the Amazon is warming “significantly” and many areas are becoming drier than in previous years, adding:
“When you combine this with things like deforestation, fires and logging…when these disturbances act together, they can have a synergistic effect.”
These issues occurring at the same time “could cause large parts of the Amazon to transition into a different ecosystem”, Flores says. He tells Carbon Brief:
“When you lose more forest, you could cross that tipping point in forest loss and then trigger a large-scale tipping point when the whole system would start accelerating to a large-scale collapse.”
The study finds that around half (47%) of the Amazon biome has a moderate potential for these changes. Larger, remote areas covering 53% of the Amazon have a low chance of ecosystem transition – which mostly accounts for protected areas and Indigenous territories.
Within these figures, the researchers find that 10% of the Amazon has a “relatively high transition potential” – meaning that it is already seeing more than two types of disturbances.
The study then looks at the three “most plausible” trajectories for Amazon ecosystems impacted by compounding stressors. These are: degraded forest, white-sand savannah and degraded open-canopy ecosystem.
Using examples of existing “disturbed” forests across the Amazon, the researchers identify these as possible futures for different parts of the forest. The figure below shows the different disturbances and feedback loops in each of these ecosystems.
1.5C ‘safe boundary’
Prof Dominick Spracklen, a professor of biosphere-atmosphere interactions at the University of Leeds, who was not involved in the study, says the research “highlights the urgency to keep both global warming and deforestation within safe limits” to protect the Amazon.
Based on their analysis, the authors say that staying within 1.5C of global warming (the aspirational limit included under the Paris Agreement) is a “safe boundary” for the Amazon forest to avoid large-scale transformations.
(A 2020 study concluded that there is a “significant likelihood” that multiple tipping points will be crossed around the world if temperatures exceed 1.5C.)
The new study suggests that ending deforestation and forest degradation – alongside boosting restoration in degraded areas – are key factors in improving the state of the Amazon.
However, Flores notes that action to stop deforestation without also stopping greenhouse gas emissions may be “useless” to prevent the forest reaching a major tipping point.
The rate of deforestation in Brazil’s Amazon soared under former president Jair Bolsonaro, but has almost halved in 2023 since Luiz Inácio Lula da Silva took over office. Meanwhile, forest loss in the Bolivian sections of the Amazon reached record-high levels in 2022.
Spracklen says this disparity “highlights the need for a pan-Amazon alliance to help collaboratively reduce deforestation”. (Last year, the leaders of the eight Amazon basin countries committed to work together to protect the rainforest – but stopped short of agreeing to end deforestation.)
Dr Patricia Pinho, the deputy science director at the Amazon Environmental Research Institute (IPAM), who was not involved in the study, says that more research is needed to assess the “cascading” effects of tipping points for people living in forest regions. She tells Carbon Brief:
“From the point of view of some people in the Amazon…A tipping point of the forest has been reached already. People are already feeling the limits of cultivating their traditional foods or encountering the biodiversity that they use for rituals, for tradition, for foods, for medicine.”
Another study author, Dr David Lapola, a researcher at the University of Campinas in Brazil and a Carbon Brief contributing editor, says the research was “necessary to investigate other potential drivers” towards this tipping point. He adds:
“Of course, there needs to be more research because even though the article points out possibilities, there is still a lot of uncertainty surrounding how the tipping point would operate and the chances of it [happening].”
Pinho adds that the “quite depressing” findings raise a lot of “red flag” issues around the Amazon, saying:
“If we don’t [take] action right now as soon as possible to avoid greenhouse emissions… climate change will continue to affect the forest in very unpredictable ways.”
She says the study is a “great contribution” to Amazon tipping point research, noting that “the bad news is that we are approaching sooner than expected those critical transitions”.
The post ‘Unprecedented’ stress in up to half of the Amazon may lead to tipping point by 2050 appeared first on Carbon Brief.
‘Unprecedented’ stress in up to half of the Amazon may lead to tipping point by 2050
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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.”
The post Heatwaves driving recent ‘surge’ in compound drought and heat extremes appeared first on Carbon Brief.
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