By John Carey for the Proceedings of the National Academy of Science.
Broadcast version by Suzanne Potter for California News Service reporting for the Pulitzer Center-Public News Service Collaboration.
Methane, one of the most potent greenhouse gases, is the major component of the biogas that seeps from countless landfills and wastewater plants. It makes sense, then, to prevent that methane from escaping into the atmosphere-indeed, hundreds of solid waste facilities across the United States have done so for decades, either flaring the biogas to burn off the methane or burning the biogas to generate electricity or heat. That gives off carbon dioxide, but still greatly reduces the greenhouse gas potential, as methane is 80 times more potent than CO2 over the first 20 years after emission.
But in recent years, government and industry have found a more profitable way to use that biogas. Taking advantage of government subsidies and using technologies that strip out the CO2 and other gases-for example, absorbing CO2 with chemicals called amines-companies turn it into pure methane that can be injected into regular natural gas pipelines and distribution networks, seamlessly blending with the chemically identical fossil natural gas. In Europe, this gas is generally called biomethane; in the United States, proponents have rebranded it as "renewable natural gas" (RNG) "to highlight the role that RNG could and should play in displacing meaningful volumes of conventional natural gas," explains Dylan Chase, spokesperson for the Coalition for Renewable Natural Gas, an industry group.
A variety of interests are increasingly pushing for more RNG. Some environmental groups, scientists, and state governments see benefits in mitigating a potent greenhouse gas. Farmers see a new source of income. And for an oil and gas industry facing global efforts to phase out natural gas and other fossil fuels in the fight against climate change, RNG offers a possible reprieve-an opportunity to keep using the trillions of dollars' worth of pipelines and other natural gas infrastructure operating. This, even as some interest groups question the "renewable" label.
So, just how green are RNG initiatives? Are they helping in the fight against climate change, or are they merely enabling companies and others to pull in profits and prolong the use of natural gas infrastructure-and even fossil natural gas? It depends, not surprisingly, on who you ask.
Harvesting Power
Methane is produced wherever microbes break down organic material in the absence of oxygen. As a result, the gas bubbles into the atmosphere from countless sources-natural ones, like wetlands or melting permafrost, and human-created ones, such as landfills, manure lagoons, and wastewater treatment plants.
People have collected and used biogas for more than a century. One of first known applications was in the late 1800s at a leper colony in Matunga, India, according to Aaron Smith, agricultural economist at the University of California, Davis (UC Davis). "They captured gas from septic tanks to run a gas engine for pumping sewage, and also for lighting and cooking," he writes (1). In many developing countries, biogas is being promoted as a cleaner, safer fuel than wood or charcoal for heating and cooking (2).
To harness biogas, the basic idea is to seal up organic matter so that oxygen can't get in and to allow bacteria to dine on the waste. Landfills are typically already covered with clay, plastic liners, or dirt, so the gases are collected by drilling wells into the mounds of waste and putting in pipes through which the biogas can flow, sometimes aided by blowers. On large dairy farms or other animal operations, a slurry of manure is funneled into a structure called an anaerobic digester, where microbes produce gas that is piped away.
Policy Driven
Making RNG economically viable, though, requires another ingredient: government policy. The biggest driver has been a California program called the Low Carbon Fuel Standard, first implemented in 2011. The policy offers credits for greenhouse gas emissions avoided in transportation fuels to lower the average carbon intensity of those fuels. By early 2019, the value of those credits had soared to nearly $200 per metric ton of CO2 (or its equivalent) avoided (3).
The program offers a financial incentive to process landfill gas and other biogas into methane and inject it into pipelines. But the subsidy is much larger for methane captured from anaerobic digesters on dairy farms than from other sources, because the program gives credit for the emissions avoided from manure lagoons. Since the dairy biomethane counts as negative emissions (not just low or zero emissions, as in landfill gas), its value has reached a sky-high level of more than $70 per million British thermal units (MMBTUs)-a value that has ranged from 8 to 20 times higher than the price of fossil natural gas. "Dairy farms say they can make more money peddling RNG credits to California than they do making milk, which is kind of crazy," says Robert Howarth, professor of ecology and evolutionary biology at Cornell University and an expert in methane emissions.
These high prices have sparked a major boom in using manure and other waste to produce biomethane. In California, most of the more than 90 anaerobic digesters and methane capture systems now in operation have come online since 2019. And since anyone who injects biomethane into a pipeline that could conceivably connect to a California system linked to transportation can get California credits, the boom has reached across the United States.
California-based RNG company Brightmark, for example, is working with dairy farms in multiple states. "If you would've told me in 2016, when I founded the company, that we would now have more than 30 projects, I wouldn't have believed it," says Brightmark CEO Bob Powell. At one of Brightmark's projects, a large dairy operation in the Finger Lakes region of New York State named Lawnhurst Farms, biomethane production is a "win-win-win for our farm, our community, and the environment," states owner Don Jensen on the Brightmark website.
Some cities, meanwhile, are interested in harvesting biogas from food. It's much more effective to keep food waste out of landfills by placing it into anaerobic digesters instead (4)-if, that is, it's possible to collect it efficiently. Residents and businesses need to sort out the waste, and municipalities need to add curbside pickups, as a landmark California law that went into effect in 2022 requires cities to do, so the practice typically only makes economic sense in dense urban areas.
Rapid Growth
The California Low Carbon Fuel Standard isn't the only policy supporting the RNG industry. Both the federal Renewable Fuel Standard and the recent Inflation Reduction Act also provide subsidies. And other cities, such as New York, are piloting special food waste collections and anaerobic digesters.
With the help of these government subsidies, both clean energy companies and the oil and gas industry are betting big on renewable gas. Back in 2011, eight companies and unions banded together to form the Coalition for Renewable Natural Gas, based in Sacramento, California. The group has now grown to 380 members, including universities, investors, and RNG developers, and major deals are being made. In December 2022, for instance, BP spent $4.1 billon buying RNG producer Archaea Energy. Shell bought Nature Energy in February for nearly $2 billion, and Chevron has formed a joint venture with Brightmark. The Coalition for Renewable Gas reports that 281 RNG facilities are in operation now in the United States, with another 180 under construction and 296 more being planned, up from just 5 n 2002. The Coalition also predicts that the renewable gas market will jump 7-fold (over 2020 levels) by 2030 and 27-fold by 2050 (5).
Phasing out fossil gas would leave oil and gas companies with massive stranded assets, so "renewable natural gas is very appealing," explains Tristan Brown, director of the Bioeconomy Development Institute at SUNY College of Environmental Science and Forestry in Syracuse, New York. "It is a drop-in fuel, so they can re-use the existing infrastructure."
Such policies and investments are good for the climate, some researchers argue. "They are doing more than anything else we've done to reduce biomethane emissions," Brown says.
Yet, at the same time, the incentives for RNG raise a deep, high-stakes question about the best path forward for fighting climate change: whether (and for how long) we should continue to use gas at all, "renewable" or not. "The central debate is: Do we want to invest in maintaining the polluting gas system we have now, or do we want to fundamentally move off of combustion sources?" says Stephan Edel, coalition coordinator of NY Renews, a coalition of more 350 environmental, justice, faith, labor, and community-based organizations.
Faux Solution
Many scientists and environmentalists worry that widespread use of biomethane is misguided. The first issue is that the supply of RNG will always be limited. In some countries where per capita consumption of natural gas is much lower than in the United States, biomethane has greater potential as a replacement fuel. In the United Kingdom, for example, a recent study from the Green Britain Foundation shows that biomethane could compensate for 72% of natural gas consumption by using grass as a gas feedstock, according to coauthor Semra Bakkaloglu, an environmental and chemical engineer at Imperial College London (6).
That's not the case in the United States. Even if it were possible to harness all of the country's food waste, landfills, manure ponds, wastewater treatment plants, and perhaps even some energy crops for gas, the resulting biofuel could replace only a fraction of current natural gas consumption, with most estimates clustering around 10 to 15 percent. "There's not nearly enough renewable natural gas," says Mary Nichols, who chaired the California Air Resources Board from 2007 to 2020, when it developed and implemented the state's Low Carbon Fuel Standard and other climate policies. And although synthetic renewable gas theoretically can be made by adding carbon to hydrogen produced from renewably generated electricity, the economic and practical hurdles of doing so are immense.
A second problem is that producing and using biogas may not be as clean and as climate friendly as its proponents claim. Just like fossil gas, it causes air pollution when burned. More important, emissions can occur at each step of the production process, from the landfill or anaerobic digester to the upgrading facility and the transport pipelines. Plus, the stuff left behind in the digesters-called the digestate-can continue to release gas after being taken out. "It doesn't take much of the methane to slip through to be a significant contributor to planetary warming," warns Cornell's Howarth.
Worrying Emissions
In fact, when Bakkaloglu measured methane emissions at or near renewable gas plants in the United Kingdom, "almost every facility we visited was emitting methane, which is worrying," she says. Overall, she found, methane emissions were more than two times higher than previously estimated, though she notes that with better monitoring and operational practices, those emissions could be significantly reduced (7).
In addition, making RNG is costly. "Anaerobic digesters could be more expensive than the value we get from stopping those methane emissions," says UC Davis' Smith. He calculated that in 2021, it cost $294 to get $68 worth of gas from cow manure (1), starkly illustrating how dependent the entire renewable gas enterprise is on government subsidies. In fact, the pace of investment in renewable gas has slowed over the past year, following a drop in the value of the California credits to only about $60 per metric ton of CO2-equivalent, down from the peak of $200.
Smith and others argue that there may be cheaper and better ways to reduce methane emissions than making RNG and injecting into pipelines. Most of the emissions from milk and beef production-as much as 80%, Howarth says-belch out from the cows themselves; those emissions can be cut by 50% or more with feed additives that inhibit methane production or modify the fermentation process in cows' guts (8). Manure could also be handled differently, Smith suggests. It could be dried and spread on fields or digested by worms, avoiding anaerobic conditions and, thus, methane emissions.
Small Role
These problems don't mean that RNG should be shunned entirely. On the contrary, the consensus among scientists and environmentalists is to collect as much biogas as possible from dairy farms, landfills, wastewater treatment plants, and other sources to cut methane emissions. But these sources should aim to use it on-site or close by, such as in co-located industries. And, perhaps even better, use it in fuel cells, which use electrochemical reactions to generate electricity, to avoid local air pollution from burning the gas. "We argue that's the best use," Howarth says. In such a scenario, biogas and RNG gas could play small, yet meaningful, roles in the global decarbonization effort.
But the debate over RNG is part of a larger policy fight over conventional natural gas, which includes the controversial idea of banning natural gas in new buildings to accelerate a transition to electric power. In 2019, Berkeley, California, was the first city to issue such a ban, against fierce opposition from the gas industry. That prohibition was tossed out by a federal court in April, but dozens of other municipalities, including New York City, San Francisco, San Jose, and Seattle, have followed suit, and in May, New York passed the first state ban. Such regulations could slow or reduce the use of natural gas, renewable or otherwise.
Meanwhile, there's a move by some environmentalists and journalists to drop the term "natural gas" in favor of more the more accurate "methane" or "methane gas," which are viewed less favorably by the public, a recent study shows (9). "Natural gas," they argue, is an industry-concocted term that makes methane seem less dangerous than it is.
Whatever the policies, experts like Nichols, now professor in residence at the Law School of the University of California, Los Angeles, argue that although RNG can play a role in greenhouse gas mitigation-particularly as a fuel or feedstock for industrial processes that are hard to electrify-ending the era of widespread use of natural gas remains a crucial milestone on the path to a lower-carbon world.
John Carey wrote this article for the Proceedings of the National Academy of Science.
get more stories like this via email
Michigan's electric vehicle industry is praising the Biden administration for its latest investments in EV manufacturing and innovation.
About $650 million will go toward retooling auto plants in Lansing and Marysville to produce newer EV models. The funding is part of the Inflation Reduction Act, going to Michigan and seven other states to make more EVs.
Sophia Schuster, policy principal for the Michigan Energy Innovation Business Council, said the money should help the state fight "brain drain." She noted Michigan is 49th in the U.S. in population growth since 1990.
"I think it's exciting to show that investments like these not only encourage people to stay and come in (to) Michigan but that there is a lot of potential for the clean energy workforce," Schuster explained. "Particularly in the auto manufacturing space."
In Michigan, the plans are expected to retain more than 1,000 jobs and create a few dozen new ones. Billions of dollars have already been spent during the Biden administration to reduce vehicle emissions and combat climate change. Transportation is the top source of emissions in the U.S.
Jane McCurry, executive director of the trade group Clean Fuels Michigan, said it is an exciting time to be in the renewable energy industry. Public and private dollars are also pouring into EV chargers, zero-emission school buses and other alternative mobility sources. She argued it will ultimately give consumers more choices.
"No matter what your choice is, you know that you can fuel it in your community, on your commute, on your way up north for vacation," McCurry emphasized. "That is where public dollars come in, is making sure that people can get everywhere they need and want to go within Michigan in a safe, efficient, effective, enjoyable way."
Gov. Gretchen Whitmer has set a statewide goal of building 100,000 EV chargers in the state by 2030, enough to support 2 million vehicles.
get more stories like this via email
A new study by the University of Illinois Urbana-Champaign suggests the long-term effects of climate change could create a higher risk of extinction for certain bird species.
Between 1980 and 2015, researchers studied more than 400 general and specialist bird species across North America. While a general species can thrive in various environments, specialist birds can only live in specific conditions.
Madhu Khanna, professor of environmental economics at the university, said the data show climate change affects migratory birds and specialist birds at greater rates than the general bird population.
"What we found is that an increase in the number of days that were hotter than 25 degrees centigrade decreased the population of birds, as well as the number of species, by about 2% or so," Khanna outlined.
Khanna pointed out specialist birds lost 7% to 16% of their populations because of climate change. She added other factors were already affecting birds, including pesticides, land use change and habitat loss. Researchers compared climate data for the same period alongside the studies.
The report found general species, like the North American sparrow, declined by almost 3% during the 25-year study. The threatened spotted owl and red-cockaded woodpecker, both specialist species, declined by 5%.
Khanna added they studied other variables that might influence birds' ability to adapt to climate change.
"Were there any changes that they might be doing in terms of their migratory routes or anything else because of this, that might reduce the negative impact of the changing climate? And we actually found no such effect," Khanna emphasized.
Khanna believes although birds are currently adapting to their respective environments, she is alarmed about the long-term effects on them if climate change continues. The Illinois Department of Natural Resources has recorded a total of 458 bird species in the state.
get more stories like this via email
By Stephen Battersby for the Proceedings of the National Academy of Sciences.
Broadcast version by Kathryn Carley for Commonwealth News Service, reporting for the Pulitzer Center-Public News Service Collaboration.
As a phrase and as a promise, net zero has been a great success. Hundreds of countries have pledged to reduce their net greenhouse gas emissions to zero by around the middle of this century. So, too, have thousands of regions, cities, and companies. Net zero has become a beacon of hope, guiding us to climate safety.
But look closely, and the beacon becomes a little blurry. Some scientists argue that net zero might lead us to rely too heavily on technologies that capture CO2 from the air. That could bring dangerous delays and unwelcome side effects, and give fossil fuel producers leeway to keep pumping and polluting. And its allure may be obscuring our need to look beyond net zero to a more ambitious goal-a world of net-negative emissions.
Some climate scientists have ideas about how we could refine net zero to make it a more focused and effective target. Others say it should only be one part of a new climate narrative. "We don't think enough about net zero, what it means, and if it's the right goal," says environmental social scientist Holly Jean Buck, of the University at Buffalo in New York.
With the fate of the planet riding on the outcome, it's vital that governments and institutions are not led astray by their climate beacon-so the debate over net zero is more urgent than ever.
The Root of Zero
The idea of net zero is firmly based on climate science. In the 2000s, scientists worked out that if we stop pouring CO2 into the atmosphere, global average temperatures should roughly stabilize. That is because two effects of Earth's oceans happen to cancel out. Today, the atmosphere is kept relatively cool by the oceans. As seawater slowly warms, we lose that cooling effect, so if emissions fall to zero, we might expect the atmosphere to carry on warming for a few decades-a phenomenon known as thermal inertia. But the oceans also keep absorbing CO2, which should roughly balance the thermal inertia and keep temperatures steady.
Net zero took off in 2018, driven by the United Nations report "Global Warming of 1.5 °C." Three years earlier, the Paris Agreement had set out a goal to limit warming to well below 2 °C above pre-industrial levels and pursue efforts to limit it to 1.5 °C. The new report laid out how the world might try to hit the more ambitious end of that goal, based on models that combine climate and economic activity. It concluded that to avoid warming of more than 1.5 °C, we would not only have to cut emissions deeply, but also remove a lot of CO2 from the atmosphere. Such removal could balance any stubborn, ongoing sources of greenhouse gases, known as residual emissions. These might include CO2 from concrete manufacture, for example, or nitrous oxide from fertilizers. So instead of absolute zero emissions, the new goal aimed for net zero, which allows some residuals to be balanced by removal.
This was only possible because technologies that remove CO2 from the air had become feasible. "Targets through the years have tended to reflect the practicality at the time of reducing emissions," says climate ecologist Stephen Pacala at Princeton University in New Jersey. "When you could envision a practical path to zero net emissions without leaving the world in poverty-all of a sudden, humanity jumped on net zero as a target."
It has undoubtedly had a galvanizing effect. "Before this, few companies had climate targets at all," says Sam Fankhauser, a climate economist at the University of Oxford in the UK. "So this is a step in the right direction."
But that shouldn't be the end of the story. "Net zero comes from the science, so it's subject to change as we learn more," says climate economist Sabine Fuss at the Mercator Research Institute on Global Commons and Climate Change in Berlin, who was a lead author on the "Global Warming of 1.5 °C" report. Climate scientists agree that the concept holds several crucial ambiguities that need to be resolved.
Zero Sum
For a start, what is the best balance between cutting emissions and removing CO2? That depends on which emission sources will be too difficult to cut. But when Buck and her colleagues analyzed 50 national long-term climate strategies, they found that countries are inconsistent in how they consider residual emissions. "The risk is that governments put things that are expensive or politically inconvenient to abate into the 'residual box,'" the paper states. That makes it hard to know how much CO2 removal we need.
According to these strategies, the average residual emissions in developed countries will be 18% of current total emissions at the time of net zero. Extended to the whole world, that would imply annual removals of at least 12 billion tonnes of CO2.
Natural solutions, such as planting forests, can't come close to reaching this quantity on their own-and in a warming world, they will be increasingly vulnerable to fire, disease, and chain saws. So the assumption is that we will use a range of novel removal methods: using machines to suck CO2 directly from the atmosphere, for example, or burning biomass to generate energy while capturing and storing the CO2 emitted.
Most of these technologies operate at small scales today, collectively removing only about two million tonnes of CO2 per year. For now, most of them are expensive to operate. Some need a lot more research and development and may yet prove difficult to scale up. That's the first problem with asking too much of carbon removal: It might not have the capacity to meet such high demand, and then we would fail to hit net zero.
The second problem is unwanted side effects. Deployed at large scale, biomass-based CO2 removal could compete for land with agriculture or with rich ecosystems, which could push up global food prices or harm biodiversity. Other approaches are also likely to have snags, especially if stretched too far. Direct air capture requires a lot of energy, which must come from a very-low-carbon source not to be counterproductive. Enhanced weathering, which involves grinding certain types of rock to speed natural CO2-absorbing chemical reactions, could create air pollution.
Without defining the levels of reductions and removals that lead to net zero, there's no clear imperative for each country or company to cut its emissions to the bone. Instead, they might hope to pay others to remove lots of CO2 on their behalf. "Everyone thinks they will buy negative emissions from someone else," says climate scientist Bas van Ruijven at the International Institute for Advanced Systems Analysis in Laxenburg, Austria.
Worse, it seems increasingly likely that CO2 removal will have to go beyond merely balancing residuals. "Now it looks like we will need net negative to meet the Paris goal," says Fuss. That means removing more CO2 from the atmosphere than we put in. Researchers in the international ENGAGE project have developed models that include a range of sociopolitical constraints, such as the ability of governments to enforce climate legislation. These models project that climate warming will overshoot the 1.5 °C target by 2050. Reversing that overshoot would require several hundred gigatonnes of CO2 removal during this century. "So you cannot have an enormous amount of residual emission, as then you need an even more enormous amount of carbon removal," says van Ruijven, who is a member of the ENGAGE project.
It may be wise to go further and try to repair some of the damage we have done, dialing down global temperatures closer to pre-industrial levels and curbing the ocean acidification caused by absorbed CO2. That would, of course, require even more removals. Despite this, companies and countries are not yet planning to reach net negative.
In some quarters, net zero is seen as a final goal. This could leave the door open for fossil-fuel production to continue at high levels and for new infrastructure that could commit us to burning those fuels for decades to come. "We haven't focused enough on the phaseout of fossil fuels," says Buck. "If we only focus on emission at the point of combustion, then we are missing half the picture." The 2023 UN Climate Change Conference (known as COP28) alluded to this problem, calling for "transitioning away from fossil fuels in energy systems." But, this falls far short of a phaseout. "It is promising that they said something, but it could have been stronger," says Buck. "What you need is a plan and a lot of resources committed to phaseout."
Zero Clarity
Net zero holds a host of other ambiguities. "Today, everybody has their own idea of what net zero means," says Fuss. "So we should take a step back and refine the concept. It is really important to get all these things straight, so we are not fooling ourselves."
For example, it's unclear whether net zero should include climate feedback effects, such as CO
2 emitted by thawing permafrost. These could require vastly more removals to prevent temperatures from rising.
Nor does the target emphasize urgency. If governments are aiming for net zero in 2050, they might feel free to kick their heels for a while. But many mitigation measures will need decades to scale up, so "it's vital to reduce emission as much as possible in the short-term," says Fuss. "You don't break something just to then repair it."
Net zero doesn't yet specify the durability of removals, either. Today's emissions will linger for centuries, so they can't simply be balanced by a form of removal that is likely to last only years or even decades. As Fankhauser et al. write: "Achieving net zero through an unsustainable combination of fossil-fuel emissions and short-term removals is ultimately pointless."
The sum should also explicitly include any knock-on effects. For example, planting forests at high latitudes can be counterproductive because they create a darker landscape that absorbs more solar heat, melting local ice and snow.
Then there is the question of whether to include other greenhouse gases, such as methane, in the net-zero sum. Methane has a much shorter lifetime in the atmosphere, so attempting to cancel out methane emissions with CO
2 removal would tend to mean more warming in the short term, and less in the long run. That could be good or bad, depending on whether it takes us past climate tipping points.
Zooming in on Zero
How can we do better? The first thing is to decide what should be classed as a residual. "We should make sure that residual emissions are truly hard to abate," says Buck. Voluntary codes are starting to address that, including the net-zero corporate standard launched by the Science Based Targets initiative, which calls for residuals to be only 5-10% of a company's current emissions.
To get removals moving, Fuss thinks that we need higher prices on carbon emissions. "If we are asking people to remove, we are asking them to perform a public service," she says, "so we should be compensating them for extracting each tonne of CO
2."
Carbon pricing could also curb fossil fuel production. Pacala led a 2023 National Academies report on accelerating decarbonization, which, among other things, recommended an economy-wide carbon tax in the United States. He says that the 2022 Inflation Reduction Act (the nation's main policy tool for moving toward net zero) omitted any such tax in order to gain political traction.
Assuming that carbon removals can scale up fast enough, it will be vital to prove how much CO
2 they are removing, through monitoring, reporting, and verification (MRV) systems. That could be challenging. "MRV is hard enough with forests, where we already have decades of experience," says Buck. "With novel techniques, it's a big challenge, and I'm not sure it's solvable on a timescale of 20 years or so." But there are some promising signs. In November 2023, the European Parliament voted to adopt a new certification scheme for removals, aiming to boost their credibility and scale. Meanwhile, advances in remote sensing and machine learning could make MRV more achievable.
As well as trying to redefine net zero, perhaps nations and societies also need to take a step back and think more broadly about what to strive for. Buck thinks that net zero should become just one among a set of targets, including reductions in fossil-fuel production and enhancing the capacity of countries to implement the clean-energy transition. She also considers the term to be fundamentally unsatisfying, a piece of accountancy that is not compelling to most people. Perhaps the world needs a more inspiring climate narrative that comes not just from scientists, but also other groups. "We need to evolve broader languages," Buck says, "and make more effort to understand what would encourage people to change their lifestyles and consumption."
Fankhauser, meanwhile, cautions against focusing on climate impacts alone. "The risk is that we maximize natural systems for carbon uptake but compromise biodiversity and other ecosystem services," he says. "We need a holistic point of view."
Climate solutions should also avoid dumping pollution or costs disproportionately on disadvantaged communities. This isn't just a moral matter. "People are not going to go along with these changes unless they see benefits in their own lives," says Pacala, who points to the plight of coal miners in the United States and other workers whose jobs may be threatened by the energy transformation. "We have to manage the jobs of legacy workers, who were previously thrown under the bus," he says.
At the moment, there is no pithy phrase to sum up these diverse aims. "Net zero is powerful because it is two words," says Fankhauser. Adding more detail could spoil that rhetorical impact. Low-residual, urgent, all-greenhouse-gas net zero, aligned with biodiversity and poverty reduction-it hardly trips off the tongue. For now, at least, researchers and policymakers may have to stick with those two words, while carefully contemplating all the things that add up to zero.
Stephen Battersby wrote this article for the Proceedings of the National Academy of Sciences.
get more stories like this via email