The fertilizer that supports around half of the food we consume has become one of the leading driver of human-influenced greenhouse gas emissions, with China, India, the US, Brazil and Russia the biggest culprits, according to the new Global Nitrous Oxide (N₂O) Budget report.
When Nobel Prize-winning chemists Fritz Haber and Carl Bosch cracked the code on how to harness ('fix') plentiful but plant-inaccessible atmospheric nitrogen for agriculture use in the early 1900s, they could not have imagined that their breakthrough that changed the world would, a century later, be reaching a dangerous tipping point in terms of cost-benefit.
Nitrogen fertilizer, along with animal manure, directly produce nearly three-quarters of our N₂O emissions. Once in the atmosphere, it's 300 times more powerful in warming the planet than carbon dioxide, and will trap heat as it lingers in the atmosphere for more than a century. N₂O also eats away at the ozone layer that shields us from dangerous solar radiation. And we've boosted its presence in the atmosphere a massive 40% since 1980.
This second report of its kind, coordinated by the Global Carbon Project and featuring an international team of researchers, the Global Nitrous Oxide Budget shines a stark spotlight on where we're at with (N₂O).
“N₂O in the atmosphere contributes to global warming as well as depleting the ozone layer," said Pep Canadell from Australia's national science agency, the CSIRO. "It is a long-lived potent greenhouse gas and has been accumulating in the atmosphere since the pre-industrial period."
Nitrogenous fertilizer, used on most crops besides legumes – which can naturally fix nitrogen – produces (N₂O), the less 'famous' greenhouse gas of the big trio alongside carbon dioxide and methane. Temporal research reveals there is 40% more (N₂O) in the atmosphere now than 40 years ago, and if 2020 to 2022 is any indication, it's on track to get far worse.
“Our report shows N₂O accumulation in the atmosphere has accelerated in the last four decades," said Canadell. "Growth rates over the past three years – from 2020-2022 – are 30% higher than any previously observed year since 1980.”
"Direct agricultural emissions" from nitrogen fertilizer and animal manure made up 74% of the anthropogenic N₂O emissions, with fossil fuel and industry, waste and wastewater, and biomass burning also contributing.
The report, which assesses global N₂O sources and sinks across 21 natural and anthropogenic categories, also shows how population demands and growing economies provide a massive trigger for these emissions.
“The once top emitter, Europe, has reduced its emissions since the 1980s by 31%, through industrial emission reductions," said study leader Hanqin Tian from Boston College. "However, emerging economies have grown in response to growing population and food demand.
“The top five country emitters by volume of anthropogenic N₂O emissions in 2020 were China (16.7%), India (10.9%), USA (5.7%), Brazil (5.3%), and Russia (4.6%)," he added.
There's an intrinsic link between climate change and agriculture and food supply. For instance, if climate variables shrink yields or degrade substrates, it's more likely we'll be using a greater amount of nitrogenous fertilizers. Which, of course, would most likely create one concerning feedback loop.
Researchers have been working to find ways producers can use these fertilizers more efficiently, to mitigate emissions without compromising yields.
“The observed atmospheric N₂O concentrations in recent years have exceeded projected levels, underscoring the importance of reducing anthropogenic N₂O emissions,” said Canadell. “For net-zero emission pathways consistent with the Paris Agreement to stabilize global temperatures below [an increase of] 2 °C (3.6 °F), anthropogenic N₂O emissions need to decline on average by around 20% by 2050 from 2019 levels.”
CSIRO initiatives underway to measure and address agriculture N₂O emissions include reducing loss of nitrogen fertilizer for cotton production, and studies on the N₂O footprint of the grains sector to make the food system more nitrogen efficient.
The Global Nitrous Oxide Budget is published in the journal Earth System Science Data.
Source: CSIRO
