The warming impact of hydrogen has been “overlooked” in projections of climate change, according to authors of the latest “global hydrogen budget”.
The study, published in Nature, is the most comprehensive analysis yet of the global hydrogen cycle, showing how the gas moves between the atmosphere, land and ocean.
Hydrogen has long been recognised as a clean alternative to fossil fuels and an important component of the green energy transition.
However, while hydrogen is not itself a greenhouse gas, rising emissions are “supercharging” the warming effect of methane, the authors say.
Increasing levels of atmospheric hydrogen have led to “indirect” warming of 0.02C over the past decade, the study finds.
The authors say that limiting leaks from future hydrogen fuel projects and rapidly cutting methane emissions will be key to securing benefits from hydrogen as a clean-burning alternative to oil and gas.
The international team of scientists behind the study also produce the annual “global carbon budget”, which saw its 20th edition published last month.
‘Supercharging’ methane
Hydrogen is the lightest and most abundant element in the universe. It is also an explosive gas that contains more energy per unit of weight than fossil fuels.
The gas has long been recognised as a clean alternative to fossil fuels, because it only emits water when burned.
There are many ways to produce hydrogen. It is typically generated in a carbon-intensive process that relies on fossil fuels. However, renewable energy can be used to produce “green hydrogen” with near-zero carbon emissions.
Hydrogen “indirectly” heats the atmosphere through its interactions with other gases. This warming is mainly due to interplay between hydrogen and methane – a potent greenhouse gas that is the second biggest contributor to human-caused global warming after CO2.
This interplay involves molecules in the atmosphere called hydroxyl radicals. These naturally occurring molecules are known as the atmosphere’s “detergents” because they react with certain greenhouse gases, such as methane, converting them into other compounds that do not warm the planet.
Prof Rob Jackson is a scientist at Stanford University and an author on the study. He explains that hydrogen also reacts with hydroxyl radicals, effectively “using up” these detergents and leaving less to react with methane.
This effectively “extends the lifetime” of methane in the atmosphere, Jackson tells Carbon Brief, leading to higher concentrations and greater warming.
There is also a reciprocal effect, where more methane in the atmosphere leads to more hydrogen. This occurs because methane reacts with oxygen in the atmosphere in a process called “oxidation”, which produces hydrogen.
Jackson tells Carbon Brief that interactions between hydrogen and methane have “not really been considered in climate circles”, adding:
“I think people don’t realise that the dominant source of hydrogen in the world today is methane in the atmosphere.”
Overall, the study estimates that increasing levels of hydrogen in the atmosphere led to global warming of 0.02C over 2010-20. This climate impact has been “overlooked”, the researchers say in a press release.
Jackson tells Carbon Brief that although this level of warming “looks fairly small”, it is still “comparable” to the warming caused by emissions of individual countries, such as France.
The hydrogen cycle
The global hydrogen budget brings together a range of observed data and models to quantify sources of hydrogen emissions as well as “sinks”, which absorb the gas from the atmosphere.
The authors find that hydrogen levels in the atmosphere increased from 523 parts per billion (ppb) in 1992 to 543ppb in 2020.
The graphic below shows the main sources (up arrows) and sinks (down arrows) of hydrogen over 2010-20.
As the figure shows, the largest single contributor to rising hydrogen emissions over 2010-20 is from the oxidation of human-produced methane. Methane emissions are on the rise due to human activity, such as from the fossil fuel industry, livestock and waste.
According to the study, 56% of atmospheric hydrogen over 2010-20 was caused by the oxidation of methane and non-methane volatile organic compounds (NMVOCs) reacting with oxygen to produce hydrogen.
(NMVOCs are chemicals that are released naturally from vegetation and more rapidly during wildfires. Human-produced emissions of NMVOCs – for example, from oil refineries or car tailpipes – are also on the rise, according to the study.)
The study also points to leakage from industrial hydrogen production as another driver of rising atmospheric hydrogen levels.
Jackson tells Carbon Brief that hydrogen leakage is on the rise “not because manufacturing is getting dirtier, but because we’re making more hydrogen from coal and natural gas”.
Hydrogen can also be produced as an unintentional byproduct from the combustion of fossil fuels. The study finds that these emissions of hydrogen are decreasing.
At the same time, natural sources of hydrogen emissions have not shown any increasing or decreasing trend over time, the authors say.
One of the largest natural sources of hydrogen is through “nitrogen fixing” – a chemical process in which nitrogen is converted into ammonia, which releases hydrogen as a byproduct. This process locks down nitrogen into the soil and ocean, where it is used by plants and algae to grow.
Meanwhile, hydrogen sinks have “increased in response to rising atmospheric hydrogen” over the past three decades, the study says.
Nearly three-quarters of the global hydrogen sink comes from hydrogen getting trapped in soil – for example, by microbes taking in hydrogen to use for energy, or hydrogen seeping into the soil through diffusion.
Dr Zutao Ouyang is an assistant professor at the University of Harvard and lead author on the study. He tells Carbon Brief that soil uptake is “the main mechanism removing hydrogen from the atmosphere”, but adds that it also has “the greatest uncertainty” because there is “not much long-term data” on this component of the hydrogen budget.
Mapped
Drawing on data including observational measurements and emissions inventories, the authors map the sources and sinks of hydrogen and their relative strength.
The maps below show the sources (top) and sinks (bottom) over 1990-2020, where darker colours indicate a stronger source or sink.
The largest “hotspots” for hydrogen emissions are in “south-east and east Asia”, according to the research. More widely, it says that “tropical regions” contribute about 60% of total hydrogen emissions.
The authors explain that these “hotspots” occur because the oxidation of methane and NMVOCs – processes that happen in the atmosphere and produce hydrogen as a byproduct – happen more quickly at higher temperatures.
They also find that these regions have more vegetation, which leads to higher NMVOC emissions.
For emissions related to human activity, east Asia and North America “contributed the most hydrogen emissions from fossil fuel combustion”, the study says, due to the “intensive fossil fuel use”.
Hydrogen emissions due to nitrogen fixation – when plants draw down nitrogen and release hydrogen as a byproduct – are highest in South America. The report links these emissions to the region’s “extensive cultivation” of crops such as soybeans and peanuts.
Dr Maria Sand is a senior researcher at CICERO and was not involved in the study. She tells Carbon Brief that the paper “provides a valuable and much-needed assessment of the global hydrogen budget”. She adds:
“By better constraining the sources and sinks of hydrogen, this study helps reduce the uncertainty in the climate impact [of hydrogen].”
Dr Nicola Warwick is a researcher at the National Centre for Atmospheric Science and assistant research professor at the University of Cambridge. She tells Carbon Brief that the study “provides an important update to our understanding of the atmospheric hydrogen budget by better constraining the key sources and sinks of hydrogen”.
She adds that better understanding of hydrogen uptake by soil – including how it responds to “climate-driven changes in soil moisture and temperature” – are “essential for reliably assessing the climate impacts of any future changes in hydrogen emissions”.
Study author Jackson tells Carbon Brief that he hopes the study will “prompt people to evaluate some of these emissions and sources and sinks in new ways and new places”.
Hydrogen economy
In the pursuit of net-zero, hydrogen may play an increasingly important role in the global energy system.
There are many ways to produce hydrogen gas. Most hydrogen is currently generated through a process called steam reforming, which brings together fossil gas and steam to produce hydrogen, with CO2 as a by-product.
According to the study, more than 90% of hydrogen produced today uses this “carbon-intensive” method.
However, electricity can be used to split water into hydrogen and oxygen atoms, in a process called electrolysis. If renewable energy is used, hydrogen can be produced and consumed with near-zero carbon emissions.
Hydrogen can be stored, liquified and transported via pipelines, trucks or ships. It can be used to make fertiliser, fuel vehicles, heat homes, generate electricity or drive heavy industry.
This potential hydrogen “economy” is shown in the graphic below. The illustrations, with numbered captions from one to three, show how hydrogen could be made, moved and used
The graphic below, from Carbon Brief’s explainer, illustrates the elements of a potential hydrogen economy.
Jackson tells Carbon Brief that, in his opinion, hydrogen is a “brilliant” choice to replace fossil fuels on-site, for industries such as steel manufacturing. However, he says he is “concerned” about “a hydrogen economy that distributes hydrogen around the world in millions of users”, because there is potential for lots of the gas to leak.
He adds:
“We know that methane leakage is bad. Hydrogen is a smaller molecule than methane. So wherever you have methane and hydrogen together, if methane leaks, hydrogen is likely to leak even more.”
The authors model hydrogen emissions under a range of future warming scenarios over the coming century.
They find that in “low-warming scenarios with high hydrogen usage”, methane emissions are low, limiting the formation of hydrogen via the oxidation of methane. In this instance, changes in atmospheric hydrogen levels depend strongly on leakage.
Meanwhile, in higher-warming scenarios, the authors find that hydrogen use is “relatively low”, but methane emissions remain “largely unmitigated”. In this instance, they find that the additional hydrogen formed through the oxidation of methane can outweigh hydrogen released through leaks.
Overall, the authors suggest that hydrogen could cause additional warming of 0.01-0.05C by the year 2100. Study author Zutao tells Carbon Brief that this additional warming was not included in the climate projections in the last assessment report from the Intergovernmental Panel on Climate Change.
The post Hydrogen emissions are ‘supercharging’ the warming impact of methane appeared first on Carbon Brief.
Hydrogen emissions are ‘supercharging’ the warming impact of methane
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 “two sessions” meeting of the National People’s Congress, including its climate strategy out to 2030, according to the Hong Kong-based South China Morning Post. The plan called for China to cut its carbon emissions per unit of gross domestic product (GDP) by 17% from 2026 to 2030, which “may allow for continued increase in emissions given the rate of GDP growth”, reported Reuters. The newswire added that the plan also had targets to reach peak coal in the next five years and replace 30m tonnes per year of coal with renewables.
ACTIVE YET PRUDENT: Bloomberg described the new plan as “cautious”, stating that it “frustrat[es] hopes for tighter policy that would drive the nation to peak carbon emissions well before president Xi Jinping’s 2030 deadline”. Carbon Brief has just published an in-depth analysis of the plan. China Daily reported that the strategy “highlights measures to promote the climate targets of peaking carbon dioxide emissions before 2030”, which China said it would work towards “actively yet prudently”.
Around the world
- EU RULES: The European Commission has proposed new “made in Europe” rules to support domestic low-carbon industries, “against fierce competition from China”, reported Agence France-Presse. Carbon Brief examined what it means for climate efforts.
- RECORD HEAT: The US National Oceanic and Atmospheric Administration has said there is a 50-60% chance that the El Niño weather pattern could return this year, amplifying the effect of global warming and potentially driving temperatures to “record highs”, according to Euronews.
- FLAGSHIP FUND: The African Development Bank’s “flagship clean energy fund” plans to more than double its financing to $2.5bn for African renewables over the next two years, reported the Associated Press.
- NO WITHDRAWAL: Vanuatu has defied US efforts to force the Pacific-island nation to drop a UN draft resolution calling on the world to implement a landmark International Court of Justice (ICJ) ruling on climate, according to the Guardian.
98
The number of nations that submitted their national reports on tackling nature loss to the UN on time – just half of the 196 countries that are part of the UN biodiversity treaty – according to analysis by Carbon Brief.
Latest climate research
- Sea levels are already “much higher than assumed” in most assessments of the threat posed by sea-level rise, due to “inadequate” modelling assumptions | Nature
- Accelerating human-caused global warming could see the Paris Agreement’s 1.5C limit crossed before 2030 | Geophysical Resea