Greenhouse gas emissions in the UK will be cut to almost zero by 2050, under the terms of a new government plan to tackle climate change.
Prime Minister Theresa May said reducing pollution would also benefit public health and cut NHS costs.Britain is the first major nation to propose this target - and it has been widely praised by green groups.
But some say the phase-out is too late to protect the climate, and others fear that the task is impossible.
The UK already has a 2050 target - to reduce emissions by 80%. That was agreed by MPs under the Climate Change Act in 2008, but will now be amended to the new, much tougher, goal.
The actual terminology used by the government is "net zero" greenhouse gases by 2050.
That means emissions from homes, transport, farming and industry will have to be avoided completely or - in the most difficult examples - offset by planting trees or sucking CO2 out of the atmosphere.
A 1.5C rise is considered the threshold for dangerous climate change.The same is true if people get hydrogen central heating instead of gas, or if they are obliged to drive electric cars rather than petrol vehicles.
But there will need to be a massive investment in clean energy generation - and that has to be funded by someone.
The government hasn't yet spelled out if the cost will fall on bill-payers, or tax-payers, or the fossil fuel firms that have caused climate change.