The United Kingdom signed a target of net-zero greenhouse gas emissions in law on Thursday, becoming the first G7 country to set such a goal and cementing the most aggressive transition toward clean energy in the world to date.

Outgoing United Kingdom Prime Minister Theresa May announced earlier this month that the UK would “eradicate its net contribution to climate change by 2050.”

It’s a legally-binding move based on the recommendations from parliament’s Committee on Climate Change issued last month. This accelerates the UK’s current target of cutting emissions 80 percent by 2050 compared to 1990 levels, a goal enshrined in the 2008 Climate Change Act. The UK’s new target is “net-zero” by 2050. It doesn’t mean “no emissions at all” but that any carbon dioxide emitted has to be offset or removed.

“Ten years after the Climate Change Act became law, now is the right moment to set a more ambitious goal,” the CCC said in a statement. “The CCC’s recommended targets, which cover all sectors of the UK, Scottish and Welsh economies, are achievable with known technologies, alongside improvements in people’s lives, and should be put into law as soon as possible.”

The law comes shortly after the UK went two whole weeks without burning coal for electricity, the longest stretch without coal since the industrial revolution.

But the UK will have to do more than curtail coal to meet its target, which demands an abrupt turn away from fossil fuels for the world’s seventh-largest economy.

Achieving these ambitions means that by 2035, all new cars must be electric. Forests must expand from covering 13 percent of land today to 17 percent by 2050. All buildings must be retrofitted and decarbonized. People must consume less meat. Thermostats in the winter should be set no higher than 19 degrees Celsius.

The UK’s new climate change law stands out in the world because it encompasses the entire UK economy, and the country is starting from an inefficient, fossil fuel-heavy baseline. So the commitment to get to zero emissions in the UK is a bigger transition than any other country has agreed to so far.

This is a much bigger shift than, say, Costa Rica, another country that’s committed to carbon neutrality. Costa Rica is a much smaller economy and already gets a much larger share of its energy from clean sources. The UK climate committee’s recommendation also reaches further than the net zero by 2045 law in Sweden, which excludes international shipping and aviation totals.

The UK, the birthplace of the Industrial Revolution, also has a long history of greenhouse gases to take into account. It ranks seventh in the world in cumulative emissions since 1750.

However, activists are still not satisfied and have said the new targets are still not aggressive enough.

Here are some things to know about the UK’s new climate change commitment.

The United Kingdom has already made significant progress in cutting greenhouse gas emissions

Carbon dioxide emissions in the UK have been trending downward since the 1970s as the country shifted away from burning coal. In 2017, UK greenhouse gas emissions fell to levels not seen since 1890:

But the UK still has a long route to zero. Fossil fuels still provide the bulk of energy in the country, so there needs to be vastly more deployment of clean energy and wider electrification across the economy.

The committee did call for electrifying transportation, one of the largest sources of emissions, as a critical tactic to fight climate change, but air travel has proved to be an extremely difficult sector to decarbonize and shows no signs of slowing down.

Hitting zero net emissions wouldn’t be any more expensive than the current target

The climate committee estimated that drawing down emissions in the United Kingdom would cost 1 to 2 percent of the country’s gross domestic product each year until 2050. That’s the same cost bracket as the current UK goal.

“Falls in cost for some of the key zero-carbon technologies mean that achieving net-zero is now possible within the economic cost that Parliament originally accepted when it passed the Climate Change Act in 2008,” according to the report.

And the UK has experienced a growing divergence between its economy and its emissions over the past two decades, which likely means the UK economy will continue to grow even as it cuts its emissions.

Activists think the new target still doesn’t go far enough

The committee report came out in April just as a massive weeks-long climate protest in London by the activist group Extinction Rebellion was winding down. Protesters achieved one of their main objectives last month when the UK Parliament declared a climate change emergency.

But Extinction Rebellion activists have described the new target as a “betrayal.”

Let’s not mince words, 2050 is a death sentence: people are already dying and this will only get worse with far off dates. Were we to put our minds to it to address the threat, the UK could embrace transformative change and decarbonise in years not decades.https://t.co/6W8KeDxRMK — Extinction Rebellion (@ExtinctionR) June 12, 2019

“2050 condemns us to a bleak future,” said Lorna Greenwood of Extinction Rebellion in a statement. “We may as well not have a target at all. Others are already dying around the world thanks to inaction and far off target setting.”

The group argues that the committee’s recommendation would only give the world a 50 percent chance of limiting temperature increases this century to 1.5 degrees Celsius.

The fight over when to reach net-zero emissions mirrors similar objections environmental groups raised in the United States last month when presidential contender Beto O’Rourke unveiled his plan to draw down US emissions to zero by 2050.

Some researchers said the UK climate committee was too optimistic in its recommendation, presuming that many aspects of a modern energy-intensive lifestyle would go unchanged. It’s also not clear on who is required to pay for the transition to a cleaner economy.

“This generational transfer of responsibility enables the CCC to maintain a thriving aviation sector and leave unquestioned the huge inequality in who is responsible for most of UK emissions,” wrote Kevin Anderson, a professor at the Tyndall Centre for Climate Change Research at the University of Manchester, in a statement. “What’s not to like — business as usual, albeit with a sizeable green twist, and influential high-emitting groups left unencumbered by policies tailored towards their carbon-intensive lifestyles.”