A few years ago, scientists studying satellite data discovered that there was an “unexpectedly large” source of CO2 emissions coming from tropical Africa, particularly over parts of Ethiopia and South Sudan.
This mysterious emissions source was so large, in fact, that if this region were a country, it would have been the second-largest emitter in the world, after China, in 2016 – releasing a total of 6bn tonnes of CO2, according to the study.
Now, newer research calls these results into question. Rather than using satellite data alone, it uses data taken by scientific aircraft travelling up and down the Atlantic Ocean off the western coast of tropical Africa.
This study finds that tropical Africa’s land acts as a net emitter of CO2 in the dry season, when practices such as biomass burning reach a peak, and a net sink in the wet season, when plants grow faster and take in more CO2 from the atmosphere. Thus, it concludes, tropical Africa’s land can be considered “neutral” in terms of its CO2 emissions.
However, the scientists that first reported the mysterious emissions tell Carbon Brief that they disagree with the new conclusions – and have a plan to explain where such large emissions could be coming from.
With neither study using data taken on the ground in Africa nor including African scientists, authors on both papers acknowledge the need for ground-based CO2 measurements to help solve the mystery.
Differing data
Africa is home to one-third of the world’s tropical rainforests, 3% of the world’s peatlands – including the world’s most extensive tropical peatland – and the majority of the world’s tropical savannahs. All of these ecosystems store large amounts of carbon.
Though the African tropics are a globally important carbon store, there have been few studies looking into the extent of year-to-year CO2 emissions from the land in this region.
Back in 2019, a study in Nature Communications sought to understand the extent of annual CO2 emissions from tropical Africa using data from Japan’s greenhouse gases observing satellite (GOSAT) and NASA’s orbiting carbon observatory (OCO-2).
The results showed that net CO2 emissions from Africa’s tropical land – the difference between the amount of CO2 absorbed and emitted by the land – totalled 5.4bn tonnes and 6bn tonnes in 2015 and 2016, respectively.
The maps below, taken from the paper’s supplementary information, show the extent of CO2 emissions from tropical land in 2015 and 2016. On the map, dark blue shows regions that acted as carbon sinks while yellow shows regions that were net emitters of CO2.
On the maps, a large yellow spot covers parts of Ethiopia and South Sudan – the source of the “unexpectedly large” emissions from Africa’s tropical land, the study’s lead author Prof Paul Palmer, a researcher of geosciences from the University of Edinburgh, told Carbon Brief back in 2019.
The newer study, published in the journal Global Biogeochemical Cycles, uses a different approach to study annual CO2 emissions from Africa’s tropical land.
This team of researchers used the NASA DC-8 Airborne Research Platform, an aeroplane that has been fitted out with equipment to conduct scientific research.
For four days across the northern hemisphere’s four seasons spread over the years 2016-18, the researchers flew south to north over the Atlantic Ocean to the west of tropical Africa, collecting CO2 measurements from the ocean surface to around 35,000 feet.
This approach allowed researchers to study the exhaust plume blown over to the Atlantic Ocean from tropical Africa. This plume contains particles such as dust, soot and wildfire smoke – along with gases such as CO2 .
The researchers then compared their data to estimates from models using the satellite data from the 2019 study.
The aircraft data found that Africa’s tropical land released far smaller emissions in the dry season, when compared to the estimates derived from satellite data. This led the researchers to conclude that the satellite data used in the 2019 study could have overestimated CO2 emissions from tropical Africa.
Instead of Africa’s tropical land being a large net source of CO2, the newer study concluded that it could actually be “neutral” in terms of annual CO2 emissions, says lead author Dr Benjamin Gaubert, a project scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. He tells Carbon Brief:
“Our findings suggest northern tropical Africa is a carbon source in the dry season and a sink in the wet season, with an annual exchange of around zero. Much of the seasonal biomass burning is inherently balanced over the year by photosynthetic uptake from grasses and shrubs.”
Conclusions questioned
Palmer, the author of the 2019 study, is not convinced by the new findings.
He argues that, because the aircraft data was collected over the Atlantic Ocean, to the west of tropical Africa, it is likely to be much more sensitive to CO2 plumes travelling over from western tropical Africa than from eastern tropical Africa – where his study found that most of the emissions were actually occurring. He tells Carbon Brief:
“I suspect – though I’m not 100% sure – that the team have shown with their analysis that west Africa, which is dominated by biomass burning, is close to neutral [for CO2 emissions], which would be less of a surprise.”
He added that while the Atlantic Ocean does receive plumes of CO2 blowing over from Africa’s tropical land, it is also likely to be affected by other sources of emissions from other parts of the world, muddying the ability to pinpoint emissions to specific regions.
Responding to these points, Dr Britton Stephens, co-author of the newer study and a senior scientist in the Earth Observing Laboratory at NCAR, tells Carbon Brief:
“It is true that the aircraft have a relatively broad region of influence that may not correspond precisely to the strongest postulated emission source of the [2019] study.”
He adds, however, that the emissions source from eastern tropical Africa identified in the 2019 study has not been exactly replicated by other research efforts using satellites. Instead, these studies typically produce “similar annual region-wide sources with very different within-region spatial patterns”.
Prof Emanuel Gloor is a researcher of CO2 emissions from tropical land at the University of Leeds, who was not an author on either paper. (He did act as a reviewer for the newer study.)
He tells Carbon Brief that the findings of the newer study – that Africa’s tropical land is neutral in CO2 terms – is much more in keeping with scientists’ understanding of the global carbon cycle:
“Essentially the result they find is exactly what you would expect.”
Mysterious emissions
As Gloor sees it, there were several issues with the 2019 study.
One of the major ones, he says, was that the scientists concluded that there could be a very large source of CO2 emissions coming from parts of Ethiopia and South Sudan – an area not only with very little infrastructure and commercial activity, but also very little forest cover. He tells Carbon Brief:
“Where would these emissions be coming from if they were really coming from Ethiopia? That’s not where you have massive amounts of biomass.”
Although the region is not covered by large areas of forest, it is home to some very carbon-rich soils, the 2019 study noted.
At the time, the scientists suggested that land degradation and deforestation could have potentially caused large amounts of carbon to be released from soils, with Palmer telling Carbon Brief in 2019:
“Substantial changes in land use over a region with high levels of soil organic carbon are conditions that could potentially release carbon from the soils.”
The detected CO2 spike could have also been influenced by the 2015-16 El Niño event, which was one of the strongest on record, another scientist not involved in the research told Carbon Brief at the time. (Warming can cause soils to release CO2 at a higher rate.)
Speaking to Carbon Brief in 2024, Palmer says that his research team do now have a firmer idea of where such a large amount of CO2 emissions could be coming from in the region comprising Ethiopia and South Sudan.
However, he declined to give more details on what this source was, arguing that it was still an area of active research and saying that he hoped to soon publish a research paper on his findings.
Data drought
Neither study uses data taken on the ground in Africa nor includes African scientists.
This is amid a backdrop of unequal participation for African scientists and institutions in global climate research.
Previous analysis by Carbon Brief found that just 1% of the most highly-cited climate research papers from the years 2017-21 featured African scientists.
And further Carbon Brief analysis showed that Africa has the lowest density of weather stations of any continent – hamstringing the ability to study how climate change could be affecting factors relevant to carbon loss from ecosystems, such as air and soil temperatures, soil moisture, rainfall and cloud cover.
Africa is the world’s second-largest continent and encompasses 20% of Earth’s land surface, meaning a lack of understanding of how its ecosystems are changing could hold consequences for scientists’ understanding of the global carbon cycle.
Carbon Brief asked the authors of both of the papers whether it was a weakness to not include data taken on the ground in Africa.
Stephens agrees that having “ground-based CO2 measurements in the region would be a big help”.
He adds, however, that to fully capture how emissions disperse in the atmosphere, these measurements should be complemented with a “systematic programme of airborne observations” – something his colleagues “recently started pursuing”.
Palmer also agrees that having on-the-ground measurements would have been preferable.
He adds that his team did have plans to travel to the region where they detected the large source of CO2 emissions via satellite data in order to take on-the-ground measurements. However, ongoing conflicts in South Sudan and Ethiopia made this impossible, he says.
The post Mystery over ‘unexpectedly large’ emissions from Africa’s tropical ecosystems appeared first on Carbon Brief.
Mystery over ‘unexpectedly large’ emissions from Africa’s tropical ecosystems
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.
Heatwaves driving recent ‘surge’ in compound drought and heat extremes
Greenhouse Gases
DeBriefed 6 March 2026: Iran energy crisis | China climate plan | Bristol’s ‘pioneering’ wind turbine
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Energy crisis
ENERGY SPIKE: US-Israeli attacks on Iran and subsequent counterattacks across the Middle East have sent energy prices “soaring”, according to Reuters. The newswire reported that the region “accounts for just under a third of global oil production and almost a fifth of gas”. The Guardian noted that shipping traffic through the strait of Hormuz, which normally ferries 20% of the world’s oil, “all but ground to a halt”. The Financial Times reported that attacks by Iran on Middle East energy facilities – notably in Qatar – triggered the “biggest rise in gas prices since Russia’s full-scale invasion of Ukraine”.
‘RISK’ AND ‘BENEFITS’: Bloomberg reported on increases in diesel prices in Europe and the US, speculating that rising fuel costs could be “a risk for president Donald Trump”. US gas producers are “poised to benefit from the big disruption in global supply”, according to CNBC. Indian government sources told the Economic Times that Russia is prepared to “fulfil India’s energy demands”. China Daily quoted experts who said “China’s energy security remains fundamentally unshaken”, thanks to “emergency stockpiles and a wide array of import channels”.
‘ESSENTIAL’ RENEWABLES: Energy analysts said governments should cut their fossil-fuel reliance by investing in renewables, “rather than just seeking non-Gulf oil and gas suppliers”, reported Climate Home News. This message was echoed by UK business secretary Peter Kyle, who said “doubling down on renewables” was “essential” amid “regional instability”, according to the Daily Telegraph.
China’s climate plan
PEAK COAL?: China has set out its next “five-year plan” at the annual “