In the bid to tackle global warming, achieving net-zero carbon dioxide emissions would be good. Net-zero greenhouse gas emissions would be even better.
In a year blighted by the pandemic, pledges to reduce planet-warming emissions to net zero have been rays of hope. South Korea and Japan both announced in October that they would achieve net-zero emissions by 2050. China had already made the pledge in September, while the European Union announced its net-zero target of 2050 earlier in the year.
The question is, net-zero emissions of what exactly?
The Road to Nothing
The EU intends to reduce not just carbon dioxide but all greenhouse gas emissions to net zero by 2050, whereas China’s pledge applies only to carbon dioxide.
With Japan, things were less clear. Prime Minister Yoshihide Suga told parliament, “Here and now I declare our goal to emit zero greenhouse gases overall by 2050, or in other words to be carbon neutral by that year.” As MPs applauded, he added “I declare we will aim to realize a decarbonized society.” Most outlets reported it as a pledge to reduce all greenhouse gases to net zero. The Japanese Prime Minister’s Office did not respond to a request for clarification.
South Korean President Moon Jae-In committed the country to achieving “carbon neutrality” by 2050 in a parliamentary address in October, and the pledge seems to apply to carbon dioxide emissions, but international observers weren’t too focused on the details. A spokesperson for the UN Secretary General praised South Korea’s “commitment to get to net-zero emissions by 2050”. Meanwhile, in response to Japan’s pledge, European Commission President Ursula von der Leyen tweeted that she was looking forward to working with the country toward achieving net-zero emissions by 2050. For the moment, the type of emissions wasn’t important.
From CO2 to CH4
To be fair, tweets and headlines are not the place for nuance, and it’s fair enough to use imprecise shorthand in initial policy announcements about change that will take a generation.
But “carbon neutrality” and “climate neutrality” are not the same thing—and the distinction matters because one is much harder to achieve than the other. As Oliver Geden of the German Institute for International and Security Affairs (SWP) has pointed out, reducing all greenhouse gas emissions to net zero will take 10 or 20 years longer than eliminating carbon dioxide emissions. For instance, if warming is to be kept to below 1.5 degrees Celsius, global carbon dioxide emissions should hit net zero in 2050, though greenhouse gas emissions need not get to zero until 2067.
New Zealand is the rare country that emphasizes the nuances in its national emissions target, which is to achieve “net zero emissions of all greenhouse gases other than biogenic methane by 2050.” In other words, New Zealand does not expect that by 2050 it will be able to remove enough carbon dioxide from the atmosphere to counteract the warming from other gases.
People generally speak of “carbon [dioxide] emissions” for good reason: they are the biggest contributor to climate change, comprising about three-quarters of global greenhouse gas emissions. Scientists even convert the other greenhouse gases into carbon dioxide equivalents for their calculations.
What’s more, carbon dioxide emissions are associated with the most well-known drivers of climate change, the transportation and electricity sectors, as well as the natural processes that counterbalance it. Burning gasoline to drive a car or coal to generate electricity? You’re emitting carbon dioxide. Planting a tree? You’re helping to absorb it.
Yet the other greenhouse gases are also major contributors to the warming of the planet. There is nitrous oxide (6 percent of overall greenhouse gas emissions), which primarily comes from agricultural practices such as applying fertilizer or burning crop residues but is also sometimes emitted during fuel combustion—these are the emissions that Volkswagen illegally masked in the 2015 Dieselgate scandal. Then there are the F-gases (2 percent), highly potent greenhouse gases mainly used in refrigeration and air conditioners. Those gases, however, are not the second-most significant driver of climate change. That honor goes to methane.
Methane on the Brain
Methane emissions make up 17 percent of greenhouse gas emissions. While the gas has a much shorter lifetime in the atmosphere than carbon dioxide, it also traps radiation more efficiently: its contribution to global warming over a 100-year period is 28 times that of carbon dioxide.
The primary source of methane emissions is not the energy sector, but rather agriculture. Pigs and cows produce methane as they digest, and their manure produces it as it decomposes. Burning trees and grasses to clear land for farming also releases methane. Flooding rice paddies, meanwhile, creates ideal conditions for methane-emitting bacteria. The decomposition of biological waste in landfills and wastewater treatment produces methane too.
Addressing these emissions is less sexy than building the perfect new Tesla, but it’s important: the Global Carbon Project says methane has been responsible for 23 percent of the global warming produced by all greenhouse gases so far. It’s also difficult to avoid them: methane emissions from agriculture are expected to be a large share of residual emissions after the EU reduces greenhouse gas emissions to net zero. Europeans will have to remove extra carbon dioxide from the atmosphere to offset the warming effect of the methane.
Incidentally, it doesn’t look like a step change on agricultural emissions is coming. Amid all the talk of the European Green Deal, in October the European Parliament agreed its position on a reform to the Common Agricultural Policy that mandates that 60 percent of farm subsidies be spent on basic income support with hardly any green strings attached. The new CAP also continues to allow creative accounting regarding which spending is classed as “sustainable.”
Blind to Leaky Pipelines
Some methane does come from fossil fuels, mostly from the production and transportation of oil and natural gas. When natural gas is burned—as its supporters never tire of repeating—it emits about half as much carbon dioxide per unit of energy consumed as does coal. But the primary component of natural gas is methane, so any natural gas that doesn’t make it into a power plant or furnace warms the planet with no benefits—and humans may have been putting more of it in the atmosphere than we realized.
A 2018 paper in the journal Science found that methane emissions from the oil and gas supply chain were 60 percent higher than the US government estimated. A February 2020 paper published in the journal Nature found that natural methane emissions, e.g. from wetlands, were smaller than assumed and therefore emissions from fossil fuels were higher. As if that weren’t enough, the authors of a March 2020 paper in the Journal of Cleaner Production found that abandoned coal mines were also leaking a lot more methane than previously thought.
New measurement technologies have improved analysts’ ability to track sneaky methane leaks, and the results are not encouraging. Last year The New York Times flew a plane with an infrared camera over the heart of shale country in Texas and found a half-dozen “super leaker” sites—one worker walked right into a plume of the invisible gas with no protection. Companies like GHGSat are using satellite imagery to monitor these emissions all over the world.
Now that policymakers have a better sense of where the methane is coming from, it would make sense to demand that the fossil fuel industry get to work mending pipeline leaks and capping and cleaning up abandoned oil and gas wells. The analysts at Carbon Tracker call these old oilfields “stranded liabilities.” Dealing with them could get quite expensive, whether for the companies themselves, institutional investors holding their shares, or the taxpayers who are left holding the bill at the end.
First Things First
Whether they apply to methane or carbon dioxide or both, the main takeaway from all these net zero announcements is that climate policy is moving. The fact that China is pledging only to eliminate carbon dioxide emissions is secondary; don’t look a gift horse in the mouth and complain about agricultural methane emissions.
Still, the “other” greenhouse gases are important and will become even more so as natural gas continues to replace coal as a fuel for electricity generation. The EU’s newly announced methane strategy is a step in the right direction; it aims above all to improve the measurement and reporting of methane emissions. Hopefully its next iteration will include binding standards requiring countries that export gas to Europe to address their methane problems at home.
Decarbonization, as the name suggests, is about getting rid of carbon dioxide. Methane and the rest must follow.