Nitrogen fertilisers, manure and other agricultural sources drove almost three-quarters of human-caused nitrous oxide emissions in recent years.
That is according to the Global Carbon Project’s second “global nitrogen budget” – an assessment of the origins and climate impacts of the world’s nitrous oxide emissions.
The research, published in Earth System Science Data, finds that nitrous oxide emissions from human activities rose by 40% over the past four decades, partly driven by growing global demand for meat and dairy.
Nitrous oxide emissions over the past decade exceeded even the highest projected levels in emissions pathways, the research finds.
Continuing to emit the greenhouse gas at current rates would “really affect” the world’s ability to achieve the long-term goal of the Paris Agreement to limit global warming to “well below” 2C, the lead author of the study tells Carbon Brief.
One expert, who was not involved in the research, says the findings show “all too clearly” that nitrous oxide emissions “are still going rapidly in the wrong direction”.
Potent greenhouse gas
Nitrous oxide (N2O) is a long-lasting greenhouse gas that is around 270 times more potent than CO2. It is the third-largest contributor to climate change, after CO2 and methane.
Various natural sources generate nitrous oxide, including tiny organisms in the world’s oceans and soils. These natural emitters accounted for 65% of all nitrous oxide emissions over 2010-19.
Human activities caused the remaining 35% of emissions, particularly nitrogen fertiliser use and manure management in agriculture. The burning of fossil fuels and biomass also produce nitrous oxide, but to a lesser extent.
The new study assesses both natural and human-caused sources of nitrous oxide to see how they have changed over time and how they are contributing to climate change.
It divides the sources and sinks into 21 categories, such as direct emissions from nitrogen use in agriculture and the exchange of CO2 between the land and atmosphere .
The researchers use a range of satellite data, models, algorithms and inventories to assess emissions over time.
The study finds that human-caused nitrous oxide emissions “significantly increased” from 1980 to 2020, growing by 40% during this time period. This rise was spurred on, in part, by growing demand for meat and dairy.
This is a jump of 10% in these human-caused emissions from the last nitrous oxide assessment, which covered data over 1980-2016.
However, the new study includes more categories than the previous global assessment, including emissions from microbe activity in the shallow waters over continental shelves. The researchers in the study say this explains some of the higher estimates in the new report.
Concentrations of the greenhouse gas in the atmosphere have also risen faster in the past three years than any other time since 1980.
Prof Hanqin Tian is the lead author of the study and an environmental sciences professor at Boston College. He tells Carbon Brief that nitrous oxide emissions continuing at current rates would “really affect the Paris climate agreement” goals.
Natural nitrous oxide emissions, on the other hand, were “relatively stable” over the period covered by the research. Tian explains:
“In terms of the total number, natural emissions are very high. But over long time periods, they stay stable. So natural emissions do not really contribute to climate change from pre-industrial times to now.”
Human-caused emissions have increased significantly. The below infographic outlines the changes in different nitrous oxide emissions sources from 2010 to 2019.
Prof Dave Reay, the chair in carbon management and education at the University of Edinburgh, who was not involved in the study, says that the research is “really significant” for both scientists and policymakers. He tells Carbon Brief:
“Nitrous oxide’s importance can sometimes be obscured by the larger climate forcing effects of CO2 and methane, yet every missed opportunity to cut nitrous oxide emissions drags the world still further away from achieving the Paris climate goals.”
The researchers highlight that human-caused nitrous oxide emissions need to be cut by at least one-fifth by 2050 to help limit long-term warming to 2C, according to the Intergovernmental Panel on Climate Change (IPCC).
Reay says this study shows “all too clearly” that these emissions are “still going rapidly in the wrong direction”.
Agricultural emissions
Agriculture was the “major driver” of increased human-caused nitrous oxide emissions over the past four decades, the study says. In total, the researchers find that the sector was responsible for 74% of these emissions over 2010-19.
While agricultural emissions increased over time, other human-caused nitrous oxide emissions from fossil fuels and industry decreased slightly between 1980 and 2020.
Cutting nitrogen use in agriculture is a “quite complex issue related to food production, food security” and a range of other issues, Tian says.
Requirements to cut nitrous oxide emissions, particularly from livestock, have been a major political issue in the Netherlands and other countries. Nitrous oxide emissions are “expected to continue rising” over the next few decades due to the growing demand for food, the study says.
Reay says that reducing nitrogen use in agriculture “can yield benefits not just for climate change mitigation, but for food production, air and water quality and biodiversity, too”. He adds:
“The array of strategies to address these losses – primarily through improving so-called nitrogen use efficiency across our food systems – are already showing positive results in some areas of Europe and south-east Asia.”
An excess of nitrogen used on the land can wash into lakes, rivers and oceans. This run-off causes damage to plants, animals and humans and spurs on toxic algae. Nitrous oxide also contributes to depletion of the ozone layer.
Top-emitting countries
The study also examines emissions in 18 different regions, finding that they grew in some countries and decreased in others over the past four decades.
China, India, the US, Brazil and Russia were the five biggest nitrous oxide emitters in 2020, the study findings show.
Human-caused emissions increased by 157% in India, 135% in China and 131% in Brazil over 1980-2020.
China alone made up 40% of the overall increase in global human-caused nitrous oxide emissions between 1980 and 2020.
Although the country remains the biggest emitter, China’s nitrous oxide emissions have decreased in recent years as a result of efforts to use nitrogen fertilisers more efficiently, Tian says.
Nitrous oxide emissions have reduced in several parts of the world since 1980: Europe, Russia, Australia, New Zealand, Japan and Korea.
Europe – the biggest nitrous oxide emitter in 1980 – has seen the most significant drop in the four decades since. Emissions fell by one-third (31%) during this time, largely due to fossil fuel and industry emissions cuts in the 1990s.
Agriculture-related nitrous oxide emissions also decreased in Europe during this time, but the drop has levelled off since the 2000s, the study notes.
Exceeding future projections
The scientists also explore how current nitrous oxide emissions compare with those from scenarios of future projections of climate change.
The charts below show how global nitrous oxide concentrations in the atmosphere (black line) compare with projections under the “Representative Concentration Pathways” (RCPs, left) and the “Shared Socioeconomic Pathways” (SSPs, right).
The charts highlight that atmospheric concentrations of the greenhouse gas over the past decade have exceeded even the projections under the very-high-emissions trajectory, RCP8.5 (red dashed line).
The researchers outline some “major uncertainties” with their findings and the scientific understanding of where nitrous oxide comes from.
These include the understanding of emissions from soils in tropical ecosystems in the Amazon Basin, the Congo Basin and south-east Asia, alongside areas using high levels of fertilisers, such as the US “corn belt”.
The study also mentions uncertainties around estimates for the impact of deforestation on nitrous oxide emissions.
The researchers propose setting up a global network to better monitor and model nitrous oxide emissions. Reay says that this is a “very timely suggestion”, adding:
“With all nations needing to submit their updated national plans for climate action in the run up to COP30 in Brazil next year, better measurement of nitrous oxide emissions holds the promise of better reporting and, crucially, better efforts to cut them.”
The post Agriculture ‘major driver’ of rise in nitrous oxide emissions over past 40 years appeared first on Carbon Brief.
Agriculture ‘major driver’ of rise in nitrous oxide emissions over past 40 years
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Drought and heatwaves occurring together – known as “compound” events – have “surged” across the world since the early 2000s, a new study shows.
Compound drought and heat events (CDHEs) can have devastating effects, creating the ideal conditions for intense wildfires, such as Australia’s “Black Summer” of 2019-20 where bushfires burned 24m hectares and killed 33 people.
The research, published in Science Advances, finds that the increase in CDHEs is predominantly being driven by events that start with a heatwave.
The global area affected by such “heatwave-led” compound events has more than doubled between 1980-2001 and 2002-23, the study says.
The rapid increase in these events over the last 23 years cannot be explained solely by global warming, the authors note.
Since the late 1990s, feedbacks between the land and the atmosphere have become stronger, making heatwaves more likely to trigger drought conditions, they explain.
One of the study authors tells Carbon Brief that societies must pay greater attention to compound events, which can “cause severe impacts on ecosystems, agriculture and society”.
Compound events
CDHEs are extreme weather events where drought and heatwave conditions occur simultaneously – or shortly after each other – in the same region.
These events are often triggered by large-scale weather patterns, such as “blocking” highs, which can produce “prolonged” hot and dry conditions, according to the study.
Prof Sang-Wook Yeh is one of the study authors and a professor at the Ewha Womans University in South Korea. He tells Carbon Brief:
“When heatwaves and droughts occur together, the two hazards reinforce each other through land-atmosphere interactions. This amplifies surface heating and soil moisture deficits, making compound events more intense and damaging than single hazards.”
CDHEs can begin with either a heatwave or a drought.
The sequence of these extremes is important, the study says, as they have different drivers and impacts.
For example, in a CDHE where the heatwave was the precursor, increased direct sunshine causes more moisture loss from soils and plants, leading to a drought.
Conversely, in an event where the drought was the precursor, the lack of soil moisture means that less of the sun’s energy goes into evaporation and more goes into warming the Earth’s surface. This produces favourable conditions for heatwaves.
The study shows that the majority of CDHEs globally start out as a drought.
In recent years, there has been increasing focus on these events due to the devastating impact they have on agriculture, ecosystems and public health.
In Russia in the summer of 2010, a compound drought-heatwave event – and the associated wildfires – caused the death of nearly 55,000 people, the study notes.
The record-breaking Pacific north-west “heat dome” in 2021 triggered extreme drought conditions that caused “significant declines” in wheat yields, as well as in barley, canola and fruit production in British Columbia and Alberta, Canada, says the study.
Increasing events
To assess how CDHEs are changing, the researchers use daily reanalysis data to identify droughts and heatwaves events. (Reanalysis data combines past observations with climate models to create a historical climate record.) Then, using an algorithm, they analyse how these events overlap in both time and space.
The study covers the period from 1980 to 2023 and the world’s land surface, excluding polar regions where CDHEs are rare.
The research finds that the area of land affected by CDHEs has “increased substantially” since the early 2000s.
Heatwave-led events have been the main contributor to this increase, the study says, with their spatial extent rising 110% between 1980-2001 and 2002-23, compared to a 59% increase for drought-led events.
The map below shows the global distribution of CDHEs over 1980-2023. The charts show the percentage of the land surface affected by a heatwave-led CDHE (red) or a drought-led CDHE (yellow) in a given year (left) and relative increase in each CDHE type (right).
The study finds that CDHEs have occurred most frequently in northern South America, the southern US, eastern Europe, central Africa and south Asia.
Threshold passed
The authors explain that the increase in heatwave-led CDHEs is related to rising global temperatures, but that this does not tell the whole story.
In the earlier 22-year period of 1980-2001, the study finds that the spatial extent of heatwave-led CDHEs rises by 1.6% per 1C of global temperature rise. For the more-recent period of 2022-23, this increases “nearly eightfold” to 13.1%.
The change suggests that the rapid increase in the heatwave-led CDHEs occurred after the global average temperature “surpasse[d] a certain temperature threshold”, the paper says.
This threshold is an absolute global average temperature of 14.3C, the authors estimate (based on an 11-year average), which the world passed around the year 2000.
Investigating the recent surge in heatwave-leading CDHEs further, the researchers find a “regime shift” in land-atmosphere dynamics “toward a persistently intensified state after the late 1990s”.
In other words, the way that drier soils drive higher surface temperatures, and vice versa, is becoming stronger, resulting in more heatwave-led compound events.
Daily data
The research has some advantages over other previous studies, Yeh says. For instance, the new work uses daily estimations of CDHEs, compared to monthly data used in past research. This is “important for capturing the detailed occurrence” of these events, says Yeh.
He adds that another advantage of their study is that it distinguishes the sequence of droughts and heatwaves, which allows them to “better understand the differences” in the characteristics of CDHEs.
Dr Meryem Tanarhte is a climate scientist at the University Hassan II in Morocco, and Dr Ruth Cerezo Mota is a climatologist and a researcher at the National Autonomous University of Mexico. Both scientists, who were not involved in the study, agree that the daily estimations give a clearer picture of how CDHEs are changing.
Cerezo-Mota adds that another major contribution of the study is its global focus. She tells Carbon Brief that in some regions, such as Mexico and Africa, there is a lack of studies on CDHEs:
“Not because the events do not occur, but perhaps because [these regions] do not have all the data or the expertise to do so.”
However, she notes that the reanalysis data used by the study does have limitations with how it represents rainfall in some parts of the world.
Compound impacts
The study notes that if CDHEs continue to intensify – particularly events where heatwaves are the precursors – they could drive declining crop productivity, increased wildfire frequency and severe public health crises.
These impacts could be “much more rapid and severe as global warming continues”, Yeh tells Carbon Brief.
Tanarhte notes that these events can be forecasted up to 10 days ahead in many regions. Furthermore, she says, the strongest impacts can be prevented “through preparedness and adaptation”, including through “water management for agriculture, heatwave mitigation measures and wildfire mitigation”.
The study recommends reassessing current risk management strategies for these compound events. It also suggests incorporating the sequences of drought and heatwaves into compound event analysis frameworks “to enhance climate risk management”.
Cerezo-Mota says that it is clear that the world needs to be prepared for the increased occurrence of these events. She tells Carbon Brief:
“These [risk assessments and strategies] need to be carried out at the local level to understand the complexities of each region.”
The post Heatwaves driving recent ‘surge’ in compound drought and heat extremes appeared first on Carbon Brief.
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