2024-07-18 09:30:03
A recent study shows that HCFC reduction policies are starting to bear fruit. But this good news also hides some bad news: at the same time, N2O emissions, linked to agriculture, have never been so high.
The term “greenhouse gas” immediately brings to mind CO2, which is considered responsible for two-thirds of the greenhouse effect caused by humans. But there are many other greenhouse gases.
In second place comes methane (CH4) emitted mainly by livestock and fermentation processes. Third place goes to N2O, or nitrous oxide, a compound directly linked to agriculture (nitrogen fertilizers and livestock effluents) and whose emissions have been increasing since 1980.
Finally, this large family also includes other gases, which are just as “dangerous”, but emitted in smaller quantities, in particular chlorinated and fluorinated gases (HCFC, HFC, CFC, etc.).
The good news: the phase-out of HCFCs is bearing fruit
HCFCs began to be used in refrigeration and air conditioning systems from the 1970s, replacing CFCs, following the discovery[1] of the destructive effect of these on the ozone layer.
However, while HCFCs have less impact on stratospheric ozone concentrations, they have a significant destructive effect. The Montreal Protocol, signed in 1987, thus established the gradual elimination of these substances. For developed countries, this began in 1996, with total elimination planned for 2030. For developing countries, this deadline is planned for 2040.
From this point of view, the paper which has just been published in the journal Nature Climate Change sheds a positive light on this ban. Indeed, the radiative forcing of HCFCs, i.e. their contribution to global warming, seems to have started to decrease as early as 2021, 5 years ahead of forecasts!
Even if it takes another 40 years for the ozone layer to return to its pre-1980 level, this is still a positive signal.
The bad news: N2O emissions still rising
According to another study, conducted by 58 international researchers and published dans Earth System Science Datathis greenhouse gas 300 times more powerful than CO2 would be responsible for 6.4% of radiative forcing since the pre-industrial era.
With thousands of measurements to support it, the study demonstrates above all that N2O emissions linked to human activities have exploded since 1980 (+40%), with a record emission of around 40 million tonnes in 2020.
These figures are all the more problematic since we would have to do the opposite: reduce emissions by at least 20% by 2050 if we want to respect the 1.5°C of the Paris Agreement!
Agriculture under attack: what actions should be implemented?
It is no surprise that the main source of anthropogenic emissions of nitrous oxide is agriculture and in particular the massive use of nitrogen products: chemical fertilizers, slurry, manure.
But beyond the simple observation, is it possible to reduce agricultural emissions of N2O and also CH4, without reducing productivity? In any case, there are avenues: proposals for action were formulated in 2013, in a report produced by INRA.
The following five proposals have a direct impact on N2O emissions:
- reduce the consumption of synthetic mineral fertilizers and make better use of organic resources;
- increase the share of legumes in large-scale cultivation and in temporary meadows;
- introduce more cover crops, intercrops and grass strips;
- optimize meadow management;
- reduce protein intake in animal rations to limit nitrogen content in effluents and N2O emissions.
What lessons can we learn from these two observations?
According to WWF99% of the substances that destroy the ozone have been eliminated, thanks to a collective and binding commitment for the States. This success therefore proves that it is possible to act, but also to win.
The fight once morest climate change concerns all human activities and is based on actions that must be implemented at a global level to be effective. Agricultural production cannot escape this, especially since it is the first to be affected by the effects of climate change.
[1] In 1974, by Rowland and Molina, two chemists from the University of California at Irvine. They received the Nobel Prize in Chemistry for this!
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