When the European Commission unveiled a draft law this week that would make binding a target to cut the bloc's planet-warming emissions to "net zero" by 2050, it exposed a sharp divide among supporters of climate action.
While that increasingly popular goal might sound ambitious, young activists, including Greta Thunberg, have called it "giving up."
"Distant net-zero emission targets will mean absolutely nothing ... if high emissions continue like now even for a few years," 34 school climate strikers from European nations wrote in an open letter.
Their call for swift action aims to avoid losing within a decade any chance of sticking to the lowest global warming limit set in the 2015 Paris Agreement, of 2.7 degrees Fahrenheit (1.5 degrees Celsius).
A United Nations climate science panel has said global emissions need to be slashed by 45% by 2030 and to net zero by mid-century to have a 50% chance of keeping warming to 2.7F.
But emissions are still rising, and countries' existing plans to cut them put the planet on track for a highly risky rise in average temperatures of at least 5.4F above pre-industrial times.
To achieve "net zero by 2050" goals – which involve producing no more climate-heating emissions than can be absorbed by planting carbon-sucking trees or otherwise trapping greenhouse gases – governments, businesses, and citizens need to do much more than make a declaration, climate analysts say.
If Britain, in particular, wants to show the world it can walk the talk as it encourages states to come to November's U.N. climate summit in Scotland with more ambitious emissions-cutting plans, then it must step up its efforts at home now, they argue.
"You've got to be on track for your own target," said Richard Black, director of the Energy and Climate Intelligence Unit (ECIU), pointing to projections that Britain will not meet its 2030 goal to reduce its emissions by 61% from 1990 levels.
That shortfall "is going to spur the government this year to come out with new policies, because otherwise they are not going to be able to wear that leadership mantle when we get to Glasgow," he told the Thomson Reuters Foundation.
Under the Paris Agreement, countries are asked to submit improved or updated climate action plans in 2020, with a view to accelerating efforts to ensure the pact's goals of limiting global warming to "well below" 3.6F, and ideally 2.7F, are met.
Until Brexit this year, Britain was covered by the European Union's "nationally determined contribution" (NDC) for the Paris Agreement – but London must now produce its own climate plan.
The Department for Business, Energy, and Industrial Strategy (BEIS) said the plan, being developed, would be published before the U.N. summit and represent an increase on Britain's "current international target."
Britain has cut its emissions by 43% since 1990, while growing the economy by three-quarters, BEIS added, describing it as the best performance among G7 nations on a per person basis.
Tasneem Essop, executive director of Climate Action Network International, a group of more than 1,300 climate organizations, said any goal of getting to net zero by 2050 had to be backed up with interim targets for the coming 10 years.
"The science says it's what we do in the next decade that is critical to achieve any long-term objective," she said.
According to a recent ECIU analysis, nearly half the world’s gross domestic product is now generated in places where authorities have set or are proposing to set a target of bringing emissions to net zero in or before 2050.
Two tiny and heavily forested countries – Suriname and Bhutan – have already achieved carbon-neutrality, and five wealthy nations – Sweden, Britain, France, Denmark, and New Zealand – have enshrined a net-zero target in law.
Britain was the first G7 nation to do so, in June 2019 – and is now working out how to put its promise into practice.
Mike Hemsley, team leader for carbon budgets at the UK Committee on Climate Change, which advises the government, said 2050 was the earliest "sensible" deadline for achieving net zero, and even that would be a tough task.
It involves big shifts such as fitting a projected 30 million households with low-carbon heating by 2050. Today only 10,000 such systems are sold each year, he said.
To meet the 2050 target, changes including more energy-efficient buildings, technology to capture and store carbon, and a doubling of clean electricity capacity will have to be in place by the mid-2030s, Mr. Hemsley noted.
Other measures to help get to net zero could include planting trees to expand the amount of wooded land in Britain from 13% to 17-19%, shifting diets away from meat and banning fossil-fuel vehicles as early as 2030, he added.
Among experts and the public, there is no firm consensus on how best to reach net zero, which will require a wide range of actions and technologies, not all of them palatable or proven.
A 2019 report by the government-sponsored UK FIRES research project on resource efficiency in industry said aiming for "absolute" zero emissions would be more honest.
Besides planting more trees, there were no short-term options to remove emissions from the atmosphere, and even a massive expansion in forestry would have only a small effect, it said.
Using machines to directly capture carbon from the air and then store or use it would require more clean energy than is likely to be available by 2050, said project leader and University of Cambridge professor Julian Allwood.
In climate policy circles, "there is a kind of optimism about what technology can deliver, assuming the incentives are right" – but that is not realistic, he said.
To achieve zero emissions without relying on carbon removal, the report said, people would have to make some sacrifices like giving up flying and eating red meat, while driving smaller electric cars and switching from gas boilers to heat-pumps.
Proposals like these are being debated by a cross-section of the British public at a citizen's climate assembly, which will finalize its recommendations in late March.
The ECIU's Black said Britain, as host of this year's U.N. summit, could offer to help the world's poorest countries and small island states work out a viable plan to put their net-zero targets into practice, drawing on its own experience.
"It's not like it's all rocket science but if you are a relatively small or medium-sized developing country, you may lack the technical capacity to do it well," he said.
This story was reported by the Thomson Reuters Foundation.