But now we learn that there’s a major dose of bad news to accompany that: What’s true for carbon dioxide is not at all true for methane, the second most important greenhouse gas. Atmospheric concentrations of this gas — which causes much sharper short-term warming, but whose effects fade far more quickly than carbon dioxide — are spiking, a team of scientists reports in an analysis published Sunday in the journal Environmental Research Letters.
Methane concentrations in the atmosphere, they report, were rising only at about .5 parts per billion per year in the early 2000s. But in the past two years, they’ve spiked by 12.5 parts per billion in 2014 and 9.9 parts per billion in 2015. With carbon dioxide rising more slowly, that means that a higher fraction of the global warming that we see will be the result of methane, at least in the next decade or so.
“Methane in the atmosphere was almost flat from about 2000 through 2006. Beginning 2007, it started upward, but in the last two years, it spiked,” said Rob Jackson, an earth scientist at Stanford University who co-wrote the study.
The paper’s first author was Marielle Saunois, a researcher at the French Laboratoire des Sciences du Climat et de l’Environnement. Saunois and Jackson are part of a larger team of researchers with the Global Carbon Project, which tracks the flows of this element across the planet (carbon is a component of both carbon dioxide and methane), and publishes a global methane budget every two years. The latest budget is here.
“Looking at the scenarios for future emissions, methane is starting to approach the most greenhouse gas-intensive scenarios,” Jackson said. “That’s bad news. We’re going in the wrong direction.”
Methane reaches the atmosphere from a complex collection of human and natural sources. It is the main component of natural gas, and so can leak from drilling operations. But it also emerges from many biological processes, including the flooding of rice paddies and “enteric fermentation” in the stomachs of ruminant animals such as cattle.
Overall, atmospheric concentrations of methane have grown from about 700 parts per billion in the preindustrial era to more than 1,840 parts per billion today. This suggests that much like with carbon dioxide, industrialization and modernization have had a long-term effect of unlocking large volumes of methane from the Earth.
There’s still far less total methane in the atmosphere than there is carbon dioxide (whose concentrations are now above 400 parts per million) — but molecule for molecule, methane packs a much stronger punch. Over a 100-year period, the emission of a given amount of methane is about 28 times as powerful when it comes to global warming as the emissions of an equivalent amount of carbon dioxide (even though the methane doesn’t stay around for that long of a time period).
If you’re a U.S. environmentalist, you may be tempted to attribute the news about spiking atmospheric methane levels to the strong growth in domestic oil and gas drilling in the past decade. After all, fugitive releases of methane to the atmosphere from drilling operations have been a major concern lately and have drawn regulatory actions from both the Environmental Protection Agency and the Interior Department under President Obama (actions that are likely to face attempted rollbacks under the incoming administration of Donald Trump).
But without denying that there may be some growth in methane emissions from global oil and gas, the new study does not point the finger there. “A substantial contribution of U.S. shale gas industry to the recent methane atmospheric increase seems unlikely,” it concludes.
Rather, it notes that two thirds of the world’s methane releases come from the tropics, not the temperate latitudes, leading the researchers to single out the agricultural sector as a more likely cause of the growth — a conclusion that may prove contentious, as this remains a matter of major debate.
“We think agriculture is the number one contributor to the increase,” Jackson said. “There’s been a secondary increase from fossil fuel use, partly because there continues to be more fossil fuels extracted.” But, he continued, “we don’t see evidence for a huge spike in fossil fuel emissions over temperate systems. We do think they’ve increased, but we don’t see evidence for leaky oil and gas wells causing this spike in global methane.”
Jackson said some of the rise is “almost certainly” coming from livestock and specifically cattle, and also pointed to rice paddies, landfills and the management of manure in agriculture.
The research thus singles out an often ignored but still major contributor to global climate change: the agricultural sector. However, it’s important to note that there remains considerable scientific uncertainty when it comes to accounting for all the complex, global sources of methane, as well as the processes that withdraw it from the atmosphere once it has been emitted. The paper fully acknowledges that these have not all been adequately understood.
When it comes to rising methane, the nature of the problem is acute but the solution has the potential to be highly effective.
Additional atmospheric methane will cause the planet to warm up faster in the coming decades and greatly increases the risk of breaking through international warming thresholds such as 1.5 or 2 degrees Celsius above preindustrial levels. But at the same time, if methane emissions can be curbed quickly, that can have the effect of buying the world needed time to address the far larger carbon dioxide problem.
“Because of methane’s high global warming potential and short lifetime in the atmosphere compared to CO2, its mitigation offers the possibility to slow climate change efficiently in a shorter time horizon,” the study argues.
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