An uptick in heat extremes, driven by human-caused climate change, has caused tropical bird populations to decline by up to 38% since the 1950s, according to a first-of-its-kind analysis.
The study combines ecological and climate attribution techniques to trace the fingerprint of fossil-fuelled climate change on declining wildlife populations.
It shows that an increase in heat extremes driven by climate change has caused tropical bird populations to decline by 25-38% in the period 1950-2020, when compared to a world without warming.
The findings could help to explain why tropical bird numbers have declined even in pristine rainforests, a phenomenon that previously mystified biologists, the scientists say.
‘Chance encounter’
Over the past few decades, an emerging field of science known as “climate attribution” has used a standardised set of techniques to trace the fingerprint of human-caused warming on different elements of the climate system, ranging from worsening extreme weather events to episodes of glacier melt.
The new research, published in Nature Ecology and Evolution, is the first to use climate attribution techniques to detect the fingerprint of climate change on declining wildlife populations.
The study came about following a “chance encounter” between lead author Dr Maximilian Kotz, a climate scientist at the Barcelona Supercomputing Center in Spain, and his co-authors, who are biodiversity experts at the University of Queensland in Australia, while Kotz was completing a research stay in Australia.
Kotz says to Carbon Brief:
“As far as we are aware, this is the first animal climate attribution study.”
The researchers decided to focus on birds, rather than other animal species, as they have the “best available data, covering a good range of different species and geographies”, he adds.
Heat extremes
The authors examine how an intensification of heat extremes could have impacted bird populations, while controlling for other factors known to affect wildlife, including average temperature increase and human pressures, such as land-use change.
Episodes of extreme heat are known to have an immediate and long-lasting impact on birds, Kotz says:
“High temperature extremes can induce direct mortality in bird populations due to hyperthermia and dehydration. Even when they don’t [kill birds immediately], there’s evidence that this can then affect body condition which, in turn, affects breeding behaviour and success.”
Using statistical techniques, the scientists first analyse historical records to identify how bird populations have responded to fluctuations in climate, including heat extremes, over 1950-2020.
The team sourced global data on bird populations from the database that underlies the Living Planet Index, put together by the environmental charity WWF. They note it is the most comprehensive database available, but still has “clear geographic biases”, with global north regions better represented than those in the global south.
They use an attribution framework to estimate the extent to which human-caused warming influenced the changes in heat extremes observed in that time period, then calculate the impact of these climate-change-driven heat extremes on bird population changes from 1950-2020.
(The authors defined “heat extremes” as temperatures within the top 1% of daily temperatures over 1940-70, with data taken from ERA5, a global reanalysis dataset, which combines data from weather stations, satellites and model output.)
To understand how this would compare to a world without climate change, the researchers subtract this impact from the historical records.
Comparing their results to the counterfactual world without climate change allowed them to quantify how bird populations have changed as a result of human-driven increases in heat extremes.
Mapped
The research finds that human-driven heat extremes have had “strong negative impacts” on bird population numbers, with those residing at lower latitudes being the most affected.
The map below shows the percentage change in bird population abundance attributed to heat extremes over 1950-2018, when compared to a world without climate change.
On the map, dark red shows large decreases in population abundance, while light blue indicates small increases. (Abundance refers to the number of individual animals in a given population.)
The research finds that birds in the tropics have experienced the largest declines attributable to heat extremes.
It concludes that an uptick in heat extremes has caused tropical bird abundance levels to decline by 25-38% in the period 1950-2020, when compared to a world without warming.
The range in the size of that impact reflects the results of different models, which each use slightly different techniques to simulate changes to bird populations, Kotz says.
Tropical turmoil
In their paper, the authors note that their finding that tropical birds have experienced the most substantial declines are “consistent” with other studies indicating that “birds in these regions may be closer to the thermal limits at which impacts start to occur”.
They add that the findings are “particularly pertinent, given recent documentation of declining tropical bird populations, even in undisturbed habitats”.
One previous study found that in a “relatively undisturbed” part of the Amazon rainforest, bird abundance declined by more than 50% from 2003 to 2022. Similar results were found in a forest in Panama.
The authors of the new study say:
“The source of such declines have been noted as unknown, yet they are of a similar order of magnitude to our estimates of the impacts of intensified heat extremes.”
Their results suggest that “in tropical realms, climate change impacts on bird populations may already be comparable to land pressures that lead to habitat destruction and degradation”, the authors say.
This has “potential ramifications” for commonly proposed conservation strategies, such as increasing the amount of land in the the tropics that is protected for nature, they continue:
“While we do not disagree that these strategies are necessary for abating tropical habitat loss…our research shows there is now an additional urgent need to investigate strategies that can allow for the persistence of tropical species that are vulnerable to heat extremes.”
In some parts of the world, scientists and conservationists are looking into how to protect wildlife from more intense and frequent climate extremes, Kotz tells Carbon Brief.
He references one project in Australia which is working to protect threatened wildlife following periods of extreme heat, drought and bushfires.
Informing forecasts
As well as shedding light on what could be behind the rapid decline of birds in the tropics, the findings also underscore the importance of examining changes in climate extremes, rather than just annual global temperature rise, says Prof Alex Pigot, a biodiversity scientist at University College London (UCL), who was not involved in the research. He tells Carbon Brief:
“Most of the models that have been used to make projections of risk to biodiversity under future climate change use long-term climate averages and so the results of this study suggest that our existing risk assessments could be missing these critical impacts of climate change.
“We urgently need to address this and develop early warning systems to be able to anticipate in advance where and when extreme heatwaves and droughts are likely to impact populations – and also rapidly scale up our monitoring of species and ecosystems so that we can reliably detect these effects and feed this information back into our models to refine our future projections for biodiversity.”
Dr Peter Soroye, a biodiversity scientist at the Wildlife Conservation Society Canada, who was also not involved in the research, agrees:
“It’s not just that the climate is getting gradually warmer every year with climate change, it’s that climate change is also driving increasingly frequent and severe extreme temperature events that are putting wildlife at risk.
“As we more fully understand the importance of extremes, it seems increasingly important to consider them when we model or project changes in biodiversity over time.”
The post Fossil-fuelled heat has caused tropical birds to decline by ‘up to 38%’ since 1950s appeared first on Carbon Brief.
Fossil-fuelled heat has caused tropical birds to decline by ‘up to 38%’ since 1950s
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Lena Luig is the head of the International Agricultural Policy Division at the Heinrich Böll Foundation, a member of the Global Alliance for the Future of Food. Anna Lappé is the Executive Director of the Global Alliance for the Future of Food.
As toxic clouds loom over Tehran and Beirut from the US and Israel’s bombardment of oil depots and civilian infrastructure in the region’s ongoing war, the world is once again witnessing the not-so-subtle connections between conflict, hunger, food insecurity and the vulnerability of global food systems dependent on fossil fuels, dominated by a few powerful countries and corporations.
The conflict in Iran is having a huge impact on the world’s fertilizer supply. The Strait of Hormuz is a critical trade route in the region for nearly half of the global supply of urea, the main synthetic fertilizer derived from natural gas through the conversion of ammonia.
With the Strait impacted by Iran’s blockades, prices of urea have shot up by 35% since the war started, just as planting season starts in many parts of the world, putting millions of farmers and consumers at risk of increasing production costs and food price spikes, resulting in food insecurity, particularly for low-income households. The World Food Programme has projected that an extra 45 million people would be pushed into acute hunger because of rises in food, oil and shipping costs, if the war continues until June.
Pesticides and synthetic fertilizer leave system fragile
On the face of it, this looks like a supply chain issue, but at the core of this crisis lies a truth about many of our food systems around the world: the instability and injustice in the very design of systems so reliant on these fossil fuel inputs for our food.
At the Global Alliance, a strategic alliance of philanthropic foundations working to transform food systems, we have been documenting the fossil fuel-food nexus, raising alarm about the fragility of a system propped up by fossil fuels, with 15% of annual fossil fuel use going into food systems, in part because of high-cost, fossil fuel-based inputs like pesticides and synthetic fertilizer. The Heinrich Böll Foundation has also been flagging this threat consistently, most recently in the Pesticide Atlas and Soil Atlas compendia.
We’ve seen this before: Russia’s invasion of Ukraine in 2022 sparked global disruptions in fertilizer supply and food price volatility. As the conflict worsened, fertilizer prices spiked – as much from input companies capitalizing on the crisis for speculation as from real cost increases from production and transport – triggering a food price crisis around the world.
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Since then, fertilizer industry profit margins have continued to soar. In 2022, the largest nine fertilizer producers increased their profit margins by more than 35% compared to the year before—when fertilizer prices were already high. As Lena Bassermann and Dr. Gideon Tups underscore in the Heinrich Böll Foundation’s Soil Atlas, the global dependencies of nitrogen fertilizer impacted economies around the world, especially state budgets in already indebted and import-dependent economies, as well as farmers across Africa.
Learning lessons from the war in Ukraine, many countries invested heavily in renewable energy and/or increased domestic oil production as a way to decrease dependency on foreign fossil fuels. But few took the same approach to reimagining domestic food systems and their food sovereignty.
Agroecology as an alternative
There is another way. Governments can adopt policy frameworks to encourage reductions in synthetic fertilizer and pesticide use, especially in regions that currently massively overuse nitrogen fertilizer. At the African Union fertilizer and Soil Health Summit in 2024, African leaders at least agreed that organic fertilizers should be subsidized as well, not only mineral fertilizers, but we can go farther in actively promoting agricultural pathways that reduce fossil fuel dependency.
In 2024, the Global Alliance organized dozens of philanthropies to call for a tenfold increase in investments to help farmers transition from fossil fuel dependency towards agroecological approaches that prioritize livelihoods, health, climate, and biodiversity.
In our research, we detail the huge opportunity to repurpose harmful subsidies currently supporting inputs like synthetic fertilizer and pesticides towards locally-sourced bio-inputs and biofertilizer production. We know this works: There are powerful stories of hope and change from those who have made this transition, despite only receiving a fraction of the financing that industrial agriculture receives, with evidence of benefits from stable incomes and livelihoods to better health and climate outcomes.
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Inspiring examples abound: G-BIACK in Kenya is training farmers how to produce their own high-quality compost; start-ups like the Evola Company in Cambodia are producing both nutrient-rich organic fertilizer and protein-rich animal feed with black soldier fly farming; Sabon Sake in Ghana is enriching sugarcane bagasse – usually organic waste – with microbial agents and earthworms to turn it into a rich vermicompost.
These efforts, grounded in ecosystems and tapping nature for soil fertility and to manage pest pressures, are just some of the countless examples around the world, tapping the skill and knowledge of millions of farmers. On a national and global policy level, the Agroecology Coalition, with 480+ members, including governments, civil society organizations, academic institutions, and philanthropic foundations, is supporting a transition toward agroecology, working with natural systems to produce abundant food, boost biodiversity, and foster community well-being.
Fertilizer industry spins “clean” products
We must also inoculate ourselves from the fertilizer industry’s public relations spin, which includes promoting the promise that their products can be produced without heavy reliance on fossil fuels. Despite experts debunking the viability of what the industry has dubbed “green hydrogen” or “green or clean ammonia”, the sector still promotes this narrative, arguing that these are produced with resource-intensive renewable energy or Carbon Capture and Storage (CCS), a costly and unreliable technology for reducing emissions.
As we mourn this conflict’s senseless destruction and death, including hundreds of children, we also recognize that peace cannot mean a return to business-as-usual. We need to upend the systems that allow the richest and most powerful to have dominion over so much.
This includes fighting for a food system that is based on genuine sovereignty and justice, free from dependency on fossil fuels, one that honors natural systems and puts power into the hands of communities and food producers themselves.
The post Middle East war is another wake-up call for fossil fuel-reliant food systems appeared first on Climate Home News.
Middle East war is another wake-up call for fossil fuel-reliant food systems
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