Welcome to Carbon Brief’s Cropped.
We handpick and explain the most important stories at the intersection of climate, land, food and nature over the past fortnight.
Key developments
Still at sea
DARK OXYGEN: Scientists discovered “dark oxygen” being produced in the deep ocean, “apparently by lumps of metal on the seafloor”, BBC News reported. The study challenges the “long-held assumption” that oxygen is produced exclusively through photosynthesis, CNN reported. Ocean scientist and lead author Dr Andrew Sweetman “observed the phenomenon time and time again over almost a decade” at several locations in the mineral-rich Clarion-Clipperton Zone in the Pacific, the outlet added. Canada’s The Metals Company, which partially funded Sweetman’s research, “attempted to poke holes in the study”, according to E&E News, but Sweetman stood by his team’s findings.
O CAPTAIN, MY CAPTAIN: The study created ripples at the ongoing seabed mining talks in Kingston, Jamaica, delegates told Carbon Brief. However, nations negotiating rules to govern the sector are also “face[d with] a critical vote” to decide who will head the International Seabed Authority (ISA), a decision “that could impact the nascent industry for years”, the Guardian wrote. Ahead of “one of the world’s most important elections…you’ve never heard of”, Foreign Policy carried an in-depth interview with Brazilian oceanographer Leticia Carvalho. Carvalho is standing for election against the ISA’s current chief Michael Lodge, “who has been criticised for allegedly having cosy ties to eager mining firms”.
RUDDERLESS WORLD: Despite heated talks, the meeting is drawing to a close with mining rules “still far from finalised”, but no mining authorised, according to the Deep Sea Conservation Coalition. Malta, Honduras, Tuvalu and Guatemala announced they were joining in the call for a “precautionary pause” on deep-sea mining, taking the number of countries pushing for a moratorium, pause or ban to 31 countries, according to the Earth Negotiations Bulletin. Palau’s president lamented: “We are once again at the mercy of powerful external forces, reminiscent of colonial exploitation that scarred our history.” For a detailed breakdown of country positions, evolving science and state of play, read Carbon Brief’s new Q&A on deep sea mining, published today.
UN hunger report
FOOD INSECURITY: Around one in five people in Africa faced hunger in 2023 as “major drivers”, including climate change and conflict, became “more frequent and severe”, a new report from the UN Food and Agriculture Organization (FAO) found. More than 700 million people around the world were undernourished in 2023, the report estimated – an increase of around 150 million people compared to 2019. “Transforming agrifood systems is more critical than ever,” the director general of the FAO, Dr Qu Dongyu, said in a statement. He added that the FAO is “committed to supporting countries in their efforts to eradicate hunger and ensure food security for all”.
AFRICA IMPACTS: Food insecurity is an issue in many parts of the world, “but Africa is at the epicentre of the crisis, with hunger on the rise across the continent”, Context News said in its coverage of the report. East Africa had the highest number of people going hungry on the continent – more than 138 million people in 2023, the outlet noted. Dr David Laborde, director of the agrifood economics division at FAO, told the New Humanitarian that “hunger level remains high, higher than in 2015” – the year that countries adopted the UN sustainable development goals for 2030, which include an aim to end hunger.
DROUGHT: Meanwhile, the prime minister of Lesotho, Sam Matekane, declared a “national food insecurity disaster” as around 700,000 people in the small African country face drought-related hunger, according to the Lesotho Times. The “critical” situation needs “national, regional and international humanitarian intervention”, the president said. Lesotho and other southern Africa countries including Zambia, Zimbabwe and Malawi were hit by drought in recent months, scorching crops and leaving millions at risk of hunger, the Associated Press reported earlier this year. A rapid attribution study found that the El Niño weather pattern was the key driver behind this drought.
Spotlight
What Venezuela’s election means for the Amazon
In this Spotlight, Carbon Brief looks at what Venezuela’s disputed election results could mean for illegal mining in the Amazon rainforest.
Earlier this week, Nicolás Maduro was declared the winner of the Venezuelan presidential election by the “government-controlled electoral authority”, the Guardian reported.
The country’s opposition disputed the results as “fraudulent”, BBC News said, while protests broke out in the country’s capital of Caracas.
Pre-election polls showed Maduro, who has served as Venezuela’s president for the past 11 years, falling behind as “voters express[ed] exhaustion over Venezuela’s economic crisis and political repression”, Al Jazeera said.
According to Mongabay, there was “little room for discussion about environmental issues” in the build-up to the election amid focus on whether the vote would be “anything close to free and fair”. The outlet said that this is “despite the fact that the country has plunged into a crisis so severe that many observers now call it an ecocide”.
Amazon impacts
Venezuela is among the world’s most biodiverse countries and it holds almost 7% of the Amazon region.
In 2022, Mongabay reported that more than 140,000 hectares of primary forest were lost in the Venezuelan areas of the Amazon over 2016-20.
New Scientist also reported in 2022 that pristine forest loss in the Venezuelan Amazon “is estimated to be increasing by around 170% annually” due to “a state-sanctioned boom in gold mining”.
Luis Jiménez, the general coordinator of the Venezuelan conservation NGO Phynatura, believes that Maduro remaining in power would continue the “exponentially accelerated” destruction of the Amazon.
He tells Carbon Brief that mining has impacted “important protected natural areas” in Venezuela, such as the Canaima and Yapacana national parks, which “apart from protecting large, megadiverse forest spaces, are home to 31 Indigenous ethnic groups”.
Jiménez believes another Maduro term would continue this “extractivist economy, which in no way benefits local communities or the rest of Venezuelans”.
Indigenous rights
In 2022, the NGO Human Rights Watch “documented horrific abuses” of Indigenous peoples “by groups controlling illegal gold mines in southern Venezuela, operating with government acquiescence”.
Last year, the Venezuelan government launched a military option to “expel more than 10,000 illegal miners from the Amazon, according to an Agence France-Presse article published in Deutsche Welle.
The article noted that Maduro said illegal mining was “destroying” the Amazon.
On deforestation, Venezuela and Bolivia were the only Amazon countries to not sign a 2021 global pledge to work towards halting deforestation by 2030.
But, in 2022, Venezuela and Colombia proposed relaunching the 1978 Amazon Cooperation Treaty Organisation, a pact between Brazil, Bolivia, Guyana, Peru, Suriname and Venezuela to protect the Amazon.
The countries then met for the first time in 14 years last August, committing to act together to prevent the rainforest “from reaching the point of no return” – but stopped short of agreeing on a common target to end deforestation.
Politicians in the US, Chile, Argentina and around the world have cast doubt over the Venezuelan election results, Reuters said. Maduro has allegedly pledged to release the full voting records, a Brazilian government official told Bloomberg, amid continued protests and tension in the country.
News and views
MILKING THE SYSTEM: Big meat and dairy corporations are “mobilis[ing] significant resources to delay and derail progressive environmental legislation”, a Changing Markets Foundation investigation found. An examination of 22 of the biggest meat and dairy corporations across four continents revealed the use of distract, delay and derail tactics, mirroring those of “big oil”. Distraction tactics, such as greenwashing, steer the spotlight away from the lack of climate action, the report said, adding that companies are using “industry-funded academic research to downplay” the sector’s environmental impact. Delay tactics “ask governments to slow down any regulation by claiming that [companies] are already taking voluntary action”. Finally, the “most aggressive” derail tactics focus on political activity, including millions spent on donations and lobbying, the report said.
COP16 THREAT MONITORING: The organising committee of the COP16 UN biodiversity summit, which will be held in Cali, Colombia in October, sought to reassure delegates after online threats from a “dissident rebel group”, reported the Guardian. The organisers reiterated that “the safety and wellbeing of all participants, attendees and collaborators are our top priority”, the newspaper added. This came after threats made by the Central General Staff (EMC) in a post on Twitter that was addressed to Colombian president Gustavo Petro and said that COP16 would “fail”. The threat came during a ceasefire breakdown between the Colombian government and factions of the EMC, which is active near Cali. The organising committee has assured that it is “closely monitoring the situation and working to establish the validity of the [threats] on social media”.
NEW GROUPS: The new European parliament agriculture committee has been formed of “predominantly right-leaning” politicians, Euronews reported. The “heightened political significance” of the committee after EU farmer protests earlier this year “has attracted top-tier MEPs and lawmakers with little ties to the agricultural world”, Euractiv reported. Some “unexpected faces” in the committee formed after the June parliament elections include a “Spanish far-right YouTuber Luis ‘Alvise’ Pérez”. Meanwhile, the bloc’s yet-to-be-announced agriculture commissioner could be Luxembourg’s Christophe Hansen from the European People’s Party, Politico speculated.
BIRD FLU BROILER: Extreme heat may have played a key role in the bird flu outbreak that infected five workers in the US state of Colorado earlier this month, the Guardian reported. The newspaper said the workers, tasked with culling poultry with the virus, became infected themselves, as their protective gear failed to work correctly amid extreme temperatures. CNN said temperatures at the time were above 40C, with large industrial fans being used to try to control the heat. “We understand those large fans…were moving so much air…the workers were finding it hard to maintain a good seal or a good fit either between the mask or with eye protection,” said Dr Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention, told CNN.
WASTE NOT: Leaders of Pacific Island states have come to an agreement with Japan over the latter’s “controversial” discharge of treated nuclear wastewater into the Pacific Ocean, according to the Pacific Islands News Association. Japanese prime minister Fumio Kishida assured the Pacific Islands Forum that the practice was being done “in compliance with international safety standards and practices”, while Pacific leaders “emphasised the need for Japan to continue providing sincere and transparent explanations” about the process. However, Prof Robert Richmond, the director of the University of Hawaii at Manoa’s Kewalo Marine Laboratory, “voiced significant concerns” about the efficacy of the treatment and the monitoring programme that is currently in place, the outlet said.
DAMAGED GOODS: A cattle rancher in Brazil has had his assets frozen in the “largest civil case brought for climate crimes in Brazil to date”, the Guardian reported. Dirceu Kruger will be compelled to pay more than $50m in “compensation for the damage he had caused to the climate through illegal deforestation”, according to the newspaper. The price tag was calculated based on the number of hectares that Kruger was found to have deforested, the average greenhouse gas emissions from damaging the rainforest and a calculation of the “social cost” of carbon. The money will be paid into the country’s climate emergency fund and the rancher will also “have to restore the land he degraded so it can become a valuable carbon sink again”, the outlet said.
Watch, read, listen
CLIMATE FINANCE: Dialogue Earth explored uncertainties around ocean communities being able to access “loss and damage” funding for those impacted by climate change.
US ELECTION: The “record on the environment” of Kamala Harris – US vice president and Democratic frontrunner for the country’s presidential election – was discussed on the NPR Living on Earth podcast.
GROWING PAINS: A feature in Al Jazeera looked at the “uncertain future” for women coffee farmers in the “conflict-ridden” eastern Democratic Republic of the Congo.
HOT WATER: The Financial Times examined the “dangerous effects of rising sea temperatures”.
New science
Indigenous food production in a carbon economy
Proceedings of the National Academy of Sciences
A new study has revealed that replacing locally harvested foods with imported market substitutes in Canada’s Inuvialuit Settlement region “would cost over C$3.1m [US$2.3m]…and emit over 1,000 tonnes of CO2-equivalent emissions” annually. The study modelled the cost of substituting local food harvests with market replacements in the region. The study found that gasoline use would add about “C$295,000 [US$213,611] [to harvesting costs] and result in 315 to 497 tonnes of emissions”, in contrast to the much higher costs and emissions associated with substituting local foods with imports. Disregarding local food systems could, therefore, “undermine emissions targets and adversely impact food security and health in Arctic Indigenous communities”, the study added.
Global atmospheric methane uptake by upland tree woody surfaces
Nature
New research found that tree bark can absorb methane from the atmosphere, meaning that the climate benefits of protecting forests “may be greater than previously assumed”. Researchers measured the methane exchange on tree stems in a range of forests in the Amazon, Panama, UK and Sweden. They found that microbes in bark could help trees to take in between 25-50m tonnes of atmospheric methane each year, with tropical forests taking in the highest levels of methane. The researchers conclude that identifying tree species that can absorb the most methane could help to tackle the global growth of the potent greenhouse gas in the atmosphere.
Cost-effectiveness of natural forest regeneration and plantations for climate mitigation
Nature Climate Change
A new research effort has created global maps illustrating what is likely to be the most cost-effective reforestation method in 138 low- and middle-income countries. To create the maps, the researchers used machine learning to combine data on the likely implementation costs of passive natural regeneration and reforestation through plantations, as well as household survey data on the opportunity costs of reforestation, data on the most suitable tree species to plant in each area and the likely carbon accumulation in each area. The research found that plantations offer the most cost-effective form of reforestation over 54% of the land included in the study, while natural regeneration would be most effective over 46% of the land.
In the diary
- 9 August: International day of the world’s Indigenous peoples
- 11-15 August: World Water Congress and Exhibition | Toronto
- 12-16 August: Working group on benefit-sharing from the use of digital sequence information | Montreal, Canada
This is an online version of Carbon Brief’s fortnightly Cropped email newsletter. Subscribe for free here.
Cropped is researched and written by Dr Giuliana Viglione, Aruna Chandrasekhar, Daisy Dunne, Orla Dwyer and Yanine Quiroz. Antara Basu also contributed to this issue. Please send tips and feedback to cropped@carbonbrief.org.
The post Cropped 31 July 2024: Deep-sea mining talks; UN hunger report; Venezuela election and the Amazon appeared first on Carbon Brief.
Cropped 31 July 2024: Deep-sea mining talks; UN hunger report; Venezuela election and the Amazon
Human-caused greenhouse gas (GHG) emissions in 2024 continued to drive global warming to record levels.
This is the stark picture that emerges in the third edition of the “Indicators of Global Climate Change” (IGCC) report, published in Earth System Science Data.
IGCC tracks changes in the climate system between Intergovernmental Panel on Climate Change (IPCC) science reports.
In doing so, the IGCC fills the gap between the IPCC’s sixth assessment (AR6) in 2021 and the seventh assessment, expected in 2028.
Following IPCC methods, this year’s assessment brings together a team of over 60 international scientists, including former IPCC authors and curators of vital global datasets.
As in previous years, it is accompanied by a user-friendly data dashboard focusing on the main policy-relevant climate indicators, including GHG emissions, human-caused warming, the rate of temperature change and the remaining global carbon budget.
Below, we explain this year’s findings, highlighting the role that humans are playing in some of the fundamental changes the global climate has seen in recent years.
(For previous IGCC reports, see Carbon Brief’s detailed coverage in 2023 and 2024.)
An ‘unexceptional’ record high
Last year likely saw global average surface temperatures hit at least 1.5C above pre-industrial levels. This aligns with other major assessments of the Earth’s climate.
Our best estimate is a rise of 1.52C (with a range of 1.39-1.65C), of which human activity contributed around 1.36C. The rest is the result of natural variability in the climate system, which also plays a role in shaping global temperatures from one year to the next.
Our estimate of 1.52C differs slightly from the 1.55C given by the World Meteorological Organisation (WMO) state of the global climate 2024 report, published earlier this year. This is because they make slightly different selections on which of the available global land and ocean temperature datasets to include. (The warming estimate has varied by similar amounts in past years and future work will aim to harmonise the approaches.)
The height of 2024’s temperatures, while unprecedented in at least the last 2,000 years, is not surprising. Given the high level of human-induced warming, we might currently expect to see annual temperatures above 1.5C on average one year in six.
However, with 2024 following an El Niño year, waters in the North Atlantic were warmer than average. These conditions raise this likelihood to an expectation that 1.5C is surpassed every other year.
From now on, we should regard 2024’s observed temperatures as unexceptional. Temperature records will continue to be broken as human-caused temperature rise also increases.
Longer-term temperature change
Despite observed global temperatures likely rising by more than 1.5C in 2024, this does not equate to a breach of the Paris Agreement’s temperature goal, which refers to long-term temperature change caused by human activity.
IGCC also looks at how temperatures are changing over the most recent decade, in line with IPCC assessments.
Over 2015-24, global average temperatures were 1.24C higher than pre-industrial levels. Of this, 1.22C was caused by human activity. So, essentially, all the global warming seen over the past decade was caused by humans.
Observed global average temperatures over 2015-24 were also 0.31C warmer than the previous decade (2005-14). This is unsurprising given the high rates of human-caused warming over the same period, reaching a best estimate of 0.27C per decade.
This rate of warming is large and unprecedented. Over land, where people live, temperatures are rising even faster than the global average, leading to record extreme temperatures.
But every fraction of a degree matters, increasing climate impacts and loss and damage that is already affecting billions of people.
Driven by emissions
Undoubtedly, these changes are being caused by GHG emissions remaining at an all-time high.
Over the last decade, human activities have released, on average, the equivalent of around 53bn tonnes of CO2 into the atmosphere each year. (The figure of 53bn tonnes expresses the total warming effect of CO2 and other greenhouse gases, such as methane and nitrous oxide, using CO2 as a reference point.)
Emissions have shown no sign of the peak by 2025 and rapid decline to net-zero required to limit global warming to 1.5C with no or limited “overshoot”.
Most of these emissions were from fossil fuels and industry. There are signs that energy use and emissions are rising due to air conditioning use during summer heatwaves. Last year also saw high levels of emissions from tropical deforestation due to forest fires, partly related to dry conditions caused by El Niño.
Notably, emissions from international aviation – the sector with the steepest drop in emissions during the Covid-19 pandemic – returned to pre-pandemic levels.
The amount of CO2 in the atmosphere, alongside the other major GHGs of methane (CH4) and nitrous oxide (N2O), is continuing to build up to record levels. Their concentrations have increased by 3.1, 3.4 and 1.7%, respectively, since the 2019 values reported in the last IPCC assessment.
At the same time, aerosol emissions, which have a cooling effect, are continuing to fall as a result of important efforts to tackle air pollution. This is currently adding to the rate of GHG warming.
Notably, cutting CH4 emissions, which are also short-lived in the atmosphere, could offset this rise. But, again, there is no real sign of a fall – despite major initiatives such as the Global Methane Pledge.
The effect of all human drivers of climate change on the Earth’s energy balance is measured as “radiative forcing”. Our estimate of this radiative forcing in 2024 is 2.97 Watts per square metre (W/m2), 9% above the value recorded in 2019 that was quoted in the last IPCC assessment.
This is shown in the figure below, which illustrates the percentage change in an array of climate indicators since the data update given in the last IPCC climate science report.
Continued emissions and rising temperatures are meanwhile rapidly eating into the remaining carbon budget, the total amount of CO2 that can be emitted if global warming is to be kept below 1.5C.
Our central estimate of the remaining carbon budget from the start of 2025 is 130bn tonnes of CO2.
This has fallen by almost three-quarters since the start of 2020. It would be exhausted in a little more than three years of global emissions, at current levels.
However, given the uncertainties involved in calculating the remaining carbon budget, the actual value could lie between 30 and 320bn tonnes, meaning that it could also be exhausted sooner – or later than expected.
Beyond global temperatures
Our assessment also shows how surplus heat is accumulating in the Earth’s system at an accelerating rate, becoming increasingly out of balance and driving changes around the world.
The data and their changes are displayed on a dedicated Climate Change Tracker platform, shown below.
The radiative forcing of 2.97 W/m2 adds heat to the climate system. As the world warms in response, much of this excess heat radiates to space, until a new balance is restored. The residual level of heating is termed the Earth’s “energy imbalance” and is an indication of how far out of balance the climate system is and the warming still to come.
This residual rate of heat entering the Earth system has now approximately doubled from levels seen in the 1970s and 1980s, to around 1W/m2 on average during the period 2012-24.
Although the ocean is storing an estimated 91% of this excess heat, mitigating some of the warming we would otherwise see at the Earth’s surface, it brings other impacts, including sea level rise and marine heatwaves.
Global average sea level rise, from both the melting of ice sheets and thermal expansion due to deep ocean warming, is included in the IGCC assessment for the first time.
We find that it has increased by around 26mm over the last six years (2019-24), more than double the long-term rate. This is the indicator that shows the clearest evidence of an acceleration.
Sea level rise is making storm surges more damaging and causing more coastal erosion, having the greatest impact on low-lying coastal areas. The 2019 IPCC special report on the oceans and cryosphere estimated that more than one billion people would be living in such low-lying coastal zones by 2050.
Multiple indicators
Overall, our indicators provide multiple lines of evidence all pointing in the same direction to provide a clear and consistent – but unsurprising and worsening – picture of the climate system.
It is also now inevitable that global temperatures will reach 1.5C of long-term warming in the next few years unless society takes drastic, transformative action – both in cutting GHG emissions and stopping deforestation.
Every year of delay brings reaching 1.5C – or even higher temperatures – closer.
This year, countries are unveiling new “nationally determined contributions” (NDCs), the national climate commitments aimed at collectively reducing GHG emissions and tackling climate change in line with the Paris Agreement.
While the plans put forward so far represent a step in the right direction, they still fall far short of what is needed to significantly reduce, let alone stop, the rate of warming.
At the same time, evidence-based decision-making relies on international expertise, collaboration and global datasets.
Our annual update relies on data from NASA and the National Oceanic and Atmospheric Administration (NOAA) and input from many of their highly respected scientists. It is this type of collaboration that allows scientists to generate well-calibrated global datasets that can be used to produce trusted data on changes in the Earth system.
It would not be possible to maintain the consistent long-term datasets employed in our study if their work is interrupted.
At a time when the planet is changing at the fastest rate since records began, we are at risk of failing to track key indicators – such as greenhouse gas concentrations or deep ocean temperatures – and losing core expertise that is vital for understanding the data.
The post Guest post: Why 2024’s global temperatures were unprecedented, but not surprising appeared first on Carbon Brief.
Guest post: Why 2024’s global temperatures were unprecedented, but not surprising
Climate Change
Guest post: How the world’s rivers are releasing billions of tonnes of ‘ancient’ carbon
The perception of how the land surface releases carbon dioxide (CO2) typically conjures up images of large-scale deforestation or farmers churning up the soil.
However, there is an intriguing – and underappreciated – role played by the world’s rivers.
Right now, plants and soils absorb about one-third of the CO2 released by human activity, similar to how much the oceans take up.
Over thousands to millions of years, some of this land-fixed carbon can end up being buried in sediments, where it eventually forms rocks.
The waters that feed rivers flow through plants, soils and rocks in landscapes, picking up and releasing carbon as they go.
This process is generally considered to be a sideways “leakage” of the carbon that is being taken up by recent plant growth.
However, the age of this carbon – how long it resided in plants and soils before it made it into rivers and then to the atmosphere – has remained a mystery.
If the carbon being released by rivers is young, then it can be considered a component of relatively quick carbon cycling.
However, if the carbon is old, then it is coming from landscape carbon stores that we thought were stable – and, therefore, represents a way these old carbon stores can be destabilised.
In our new study, published in Nature, we show that almost 60% of the carbon being released to the atmosphere by rivers is from these older sources.
In total, this means the world’s rivers emit more than 7bn tonnes of CO2 to the atmosphere each year – more than the annual fossil-fuel emissions from North America.
This means that there is a significant leak of carbon from old stores that we thought were safely locked away.
Previous work has shown that local land-use change, such as deforestation and climate-driven permafrost thaw, will directly release old carbon into rivers. Whether this is happening at the global scale remains a significant unknown for now.
Who are you calling old?
How do you tell how old carbon is? We employ the same technique that is used to determine the age of an archaeological relic or to verify the age of a vintage wine – that is, radiocarbon dating.
Radiocarbon is the radioactive isotope of carbon, which decays at a known rate. This enables us to determine the age of carbon-based materials dating back to a maximum age of about 60,000 years old.
We know that some of the carbon that rivers release is very young, a product of recent CO2 uptake by plants.
We also know that rivers can receive carbon from much older sources, such as the decomposition of deep soils by microbes and soil organisms or the weathering and erosion of ancient carbon in rocks.
Soil decomposition can release carbon ranging from a few years to tens of thousands of years. An example of very old soil carbon release is from thawing permafrost.
Rock weathering and erosion releases carbon that is millions of years old. This is sometimes referred to as “radiocarbon-dead” because it is so old all the radiocarbon has decayed.
Rivers are emitting old carbon
In our new study, we compile new and existing radiocarbon dates of the CO2 emissions from around 700 stretches of river around the world.
We find that almost 60% of the carbon being released to the atmosphere by rivers is from older sources (hundreds to thousands of years old, or older), such as old soil and ancient rock carbon.
In the figure below, we suggest how different processes taking place within a landscape can release carbon of different ages into rivers, driving its direct emission to the atmosphere.
So, while rivers are leaking some modern carbon from plants and soils as part of the landscape processes that remove CO2 from the atmosphere, rivers are also leaking carbon from much older landscape carbon stores.
One major implication of this finding is that modern plants and soils are leaking less carbon back to the atmosphere than previously thought, making them more important for mitigating human-caused climate change.
We find that the proportion of old carbon contributing to river emissions varies across different ecosystems and the underlying geology of the landscapes they drain.
In the figure below, we show that landscapes underlain by sedimentary rocks, which are the most likely to contain substantial ancient (or “petrogenic”) carbon, also had the oldest river emissions. We also show that the type of ecosystem (biome) was also important, although the patterns were less clear.
What is obvious is that at least some old carbon was common across most of the rivers we observed, regardless of size and location.
We provide evidence that there is a geological control on river emissions. And the variability in the ecosystem also indicates important controlling factors, such as soil characteristics, vegetation type and climate – especially rainfall patterns and temperature which are known to impact the rate of carbon release from soils and rock weathering.
Are old carbon stores stable?
Long-term carbon storage in soils and rocks is an important process regulating global climate.
For example, the UK’s peatlands are important for regulating climate because they can store carbon for thousands of years. That is why restoring peatlands is such a great climate solution.
Rivers emit more than 7bn tonnes of CO2 to the atmosphere each year – that’s equivalent to about 10-20% of the global emissions from fossil fuel burning annually.
If 60% of river carbon emissions are coming from old carbon stores, then this constitutes a significant leak of carbon from old stores we thought were safely locked away.
Another major implication of our study is that these old carbon stores can be mobilised and routed directly to the atmosphere by rivers, which would exacerbate climate change if these stores are further destabilised.
As can be seen in the figure below, we found that river carbon emissions appeared to be getting older since measurements first began in the 1990s (lower F14Catm means older radiocarbon ages).
We found that river carbon emissions appeared to be getting older since measurements first began in the 1990s.
While there are several caveats to interpreting this trend, it is a warning sign that human activities, especially climate change, could intensify the release of carbon to the atmosphere via rivers.
Given the strong link between soil carbon and river emissions, if this trend is a sign of human activity disturbing the global carbon cycle, it is likely due to landscape disturbance mobilising soil carbon.
Using rivers to monitor global soil carbon storage
Rivers collect waters from across the landscapes they flow through and therefore provide a tool to track processes happening out of sight.
A drop of water landing in a landscape travels through soils and rock before reaching the river, and its chemistry, including its radiocarbon age, reflects the processes occurring within the landscape.
Monitoring the age of carbon in rivers can therefore tell you a lot about whether their landscapes are storing or releasing carbon.
This has been shown to help identify carbon loss in degraded tropical peatlands, thawing Arctic permafrost and due to deforestation.
River radiocarbon is sensitive to environmental change and could therefore be a powerful monitoring tool for detecting the onset of climate tipping points or the success of landscape restoration projects, for example.
While we present data spread out across the world, there are quite a few gaps for important regions, notably where glacier change is happening and others where droughts and flood frequencies are changing.
These include areas with low amounts of data in Greenland, the African continent, the Arctic and Boreal zones, the Middle East, eastern Europe, western Russia, Central Asia, Australasia and South America outside of the Amazon.
All these regions have the potential to store carbon in the long-term and we do not yet know if these carbon stores are stable or not under present and future climate change.
River radiocarbon offers a powerful method to keep tabs on the health of global ecosystems both now and into the future.
The post Guest post: How the world’s rivers are releasing billions of tonnes of ‘ancient’ carbon appeared first on Carbon Brief.
Guest post: How the world’s rivers are releasing billions of tonnes of ‘ancient’ carbon
Climate Change
A National Quest for Uranium Comes to Remote Western Alaska, Raising Fears in a Nearby Village
Demand for low-carbon nuclear energy could boost uranium prospects on Alaska’s Seward Peninsula. But residents of the small village of Elim fear a mine would pollute the river they depend on.
This story was published in partnership with Northern Journal and is the second in a two-story series.
A National Quest for Uranium Comes to Remote Western Alaska, Raising Fears in a Nearby Village
The Senate makes some improvements, but our defense work continues
Guest post: Why 2024’s global temperatures were unprecedented, but not surprising
Guest post: How the world’s rivers are releasing billions of tonnes of ‘ancient’ carbon
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