Why is the IPCC emphasizing methane in its new report?

• Where is the science in the knowledge of climate systems and climate change?

  It is on this question that the Intergovernmental Panel on Climate Change (IPCC) looked into, in a report published on Monday.

• Unsurprisingly, this new publication records an acceleration in global warming with its corollary: the increase in extreme weather events.

  The IPCC is thus pushing more than ever to reduce our greenhouse gas emissions.

• And reducing our CO2 emissions, the first gas contributing to global warming, will not be enough.

  The IPCC also highlights the issue of reducing our methane emissions.

  The most effective way even to contain climate change?

"Recent observed climate changes are widespread, rapid, intensifying and unprecedented for thousands of years" ... The Intergovernmental Panel on Climate Change (IPCC) published on Monday the first of three parts of his evaluation report, a long-term work that he had not released since 2014.

This first part - to be seen as a major update of the state of scientific knowledge on past, present and future climate change - leaves little room for doubt: “unless we reduce our greenhouse gases immediately, fast and on a large scale, the objective of containing global warming to + 1.5 ° C compared to the pre-industrial era will be elusive, ”insists the IPCC.

“CO2, the dominant greenhouse gas…”, but…

The challenge then, recalls the Chinese climatologist Panmao Zhai, co-chairman of group 1 of the IPCC, is to achieve carbon neutrality before 2050, this point of equilibrium from which we will not emit more CO2 into the atmosphere than we are able to absorb it, mainly via natural carbon sinks (oceans, forests, grasslands, mangroves). The latter having a limited absorption capacity and even tending to decrease, it will therefore inevitably be necessary to accelerate the reduction of our CO2 emissions.

"It is the dominant greenhouse gas," recalls Pascale Braconnot, climatologist at the Laboratory of Climate and Environmental Sciences (LSCE-IPSL), among the 234 authors to have contributed to the IPCC report. We are already on a global warming of + 1.1 ° C compared to the pre-industrial era. CO2 emissions contribute 0.75 ° C to this warming and in the five prospective scenarios that the IPCC takes into account [from the most optimistic (with the greatest reduction in GHGs) to the most pessimistic], CO2 remains at each time the first source of global warming. "

But just behind, there is methane (CH4), often presented as the great forgotten of the climate.

However, it counts for 0.5 ° C on these + 1.1 ° C already recorded.

As with CO2, its concentration increases in the atmosphere.

+ 156% since 1750 [against + 47% for CO2] and over 6% over the last ten years.

"In 2019, CH4 concentrations have never been so high for at least 800,000 years", points out the IPCC.

Fortunately for us, this gas degrades more quickly in the atmosphere than CO2, because otherwise it has a much more powerful heating power than the latter *.

Avoidable methane emissions?

Part of the methane emitted into the atmosphere is naturally emitted, in particular via the decomposition of plants. But human activities, too, generate it. In particular agriculture, in particular the breeding of cattle which release methane into the atmosphere by digesting (their farts and their burps to be clear). Not nothing, agriculture would represent nearly a quarter of the total estimated methane emissions.

The other major emitting sector is that of hydrocarbons (gas and oil) where methane releases occur at different stages.

From exploration to distribution, including production and can be either accidental (leaks) or deliberate (gas released or "flared" for safety reasons. According to the International Energy Agency (IEA), oil and gas companies emit more than 75 million tonnes of methane into the atmosphere each year, emissions increasingly tracked by satellites, notably the European Sentinel-5P.

The methane hunt, the golden opportunity?

Infuriating… Published last June, a UN report - the Global methane assessment - indicated that it was possible to reduce methane emissions by 40% in 2030, mainly using methods that are easily deployable, inexpensive or remunerative in 85% of cases. Should we then make it the priority, as suggested by Durdwood Zaelke, president of the Institute for Governance and Sustainable Development and one of the examiners of the report published on Monday. "Reducing our methane emissions is the greatest opportunity to slow global warming by 2040," he said in remarks taken up by the

 Guardian on

 Friday.

Sophie Szopa, CEA research director at LSCE and coordinator of chapter 6 of the IPCC report, tempers.

“The only effective way to achieve carbon neutrality and to control global warming over the long term is to lower our CO2 emissions,” she insists.

But reducing our methane emissions must come in addition.

”If only because this battle could help to lower global warming by a few tenths of a degree.

Which is far from superfluous.

A win-win effect

But the stakes go beyond. The hunt for fine particles in the atmosphere, launched around the world for issues of air pollution and, by extension, health, paradoxically has harmful effects on the rise in temperatures. “Once emitted into the atmosphere, some of these aerosols will transform and effectively have a cooling effect,” explains Sophie Szopa. This is the case with sulfur dioxide which will turn into sulphates. These aerosols will act as parasols by preventing the incident radiation (ray of light that has not undergone any refraction) from descending into the atmosphere. But these aerosols will also serve as condensation nuclei and thus change the cloud cover, which contributes indirectly to this cooling. "

Thus, globally, "these fine particles" mask "today a third of global warming linked to greenhouse gases, so that by reducing them, global warming could worsen in the short term", continues Sophie. Szopa.

Impossible to choose between these two fights.

Methane could however solve this dilemma.

"Because it has a short life, drastically lowering its emissions would give hope for a rapid drop in its atmospheric concentrations and therefore more immediate results on global warming than with CO2", continues Sophie Szopa.

Enough to offset, at least in part, the harmful effect that the fight against air pollution will have on global warming.

Sophie Szopa adds yet another reason to this need not to neglect the tracking of our methane emissions.

“Once emitted into the atmosphere, unlike CO2, methane will react chemically and produce ozone,” continues the climatologist.

However, ozone is a pollutant harmful to health and which also alters ecosystems and significantly harms crop yields.

Tracking down methane would therefore kill two birds with one stone, both on global warming and on health.

A “win-win” effect on which the IPCC particularly insists in its new report.

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* When carbon dioxide (CO2) stays in the atmosphere for a hundred years, methane only stays there for a dozen years.

On a century scale, methane is still 25 times more powerful than carbon dioxide in global warming potential (GWP), recalls Futura Sciences.

In equal quantities, methane is therefore more powerful in greenhouse effect than CO2.

But there aren't as many methane emissions as there are carbon dioxide emissions.

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