The UK cannot go climate neutral much before 2050 unless people stop flying and eating red meat almost completely, a report says.
But it warns that the British public do not look ready to take such steps and substantially change their lifestyle.
The report challenges the views of campaign group Extinction Rebellion.
It believes the UK target of climate neutrality by 2050 will result in harm to the climate.
The claim comes from the government-funded research group Energy Systems Catapult, whose computer models are used by the Committee on Climate Change, which advises government.
Its report says: "A number of groups have called for net zero to be accelerated to 2025, 2030 or 2040.
"Achieving net zero significantly earlier than 2050 in our modelling exceeds even our most speculative measures, with rates of change for power, heat and road transport that push against the bounds of plausibility."
Glimmer of good news
But the authors offer some optimism too. They calculate that the UK can cut emissions fast enough to be climate neutral by 2050 – but only if ministers act much more quickly.
They say the government urgently needs to invest in three key technologies: carbon capture and storage with bioenergy crops; hydrogen for a wide variety of uses; and advanced nuclear power.
The report modelled options for society to 2050. It concluded that if decisions are made early, the cost of climate neutrality can be held down to 1-2% of national wealth - GDP.
Scenarios rely on some technologies still in their infancy, which will be controversial. For instance, it draws heavily on burning energy crops, capturing the carbon emissions and burying them underground.
It says hydrogen use will need to grow to supply industry, heat and heavy transport.
Electricity generation will need to double with heavy reliance on solar power and offshore wind.
Controversially, it calls for small, modular nuclear reactors to support three-quarters of heating in cities through district heating systems. Modular reactors are much smaller than conventional reactors, and brought to a site in a kit of parts to be assembled.
It warns that livestock production for dairy and meat may need to be cut by 50% rather than the 20% currently envisaged by the Committee on Climate Change. And people will need to eat less meat and dairy by the same amount.
The report s author, Scott Milne, said: “Whichever pathway the UK takes, innovation, investment and inducements across low-carbon technology, land use and lifestyle are essential to achieve net zero.
Image copyrightSCIENCE PHOTO LIBRARYImage captionAdopting new technologies, such as hydrogen energy, will be crucial
"And there are massive economic opportunities for the UK to lead the world in these areas."
However, the report warns that the public do not appear ready for substantial lifestyle changes. It warns, for instance, that if people s homes are better insulated, they may choose to spend the same amount on heating to deliver a warmer home.
It says: “Early evidence suggests a general willingness to adopt new technologies (such as new heating or mobility) as long as these can deliver the same experiences as before.
“Conversely, approaching the subject of dietary change or aviation often elicits a more resistant and emotional response.”
Some experts will be critical of the report s expectation that new technologies such as carbon capture and storage will be rapidly adopted.
A recent report said it was unrealistic to expect that carbon capture and hydrogen will develop fast enough to achieve the net zero target.
A spokesperson for Extinction Rebellion told BBC News: "The global response to coronavirus shows we can radically address crises if we put our minds to it. Meanwhile, the net zero date has not been put to the people of the UK.
"The science tells us that net zero by 2050 means a hell of a lot worse than giving up flying and red meat - people are dying now around the world as you read this due to governmental inaction."
The report was not welcomed by the National Beef Association.
Its spokesman Neil Shand told BBC News that scientific studies typically underestimate the role of livestock in capturing carbon in the soil.
He said: “It does seem rather unfortunate that the report links beef production and aviation in this way.
“The timing is more than a little ironic; the shops are full of people panic-buying and it seems clear that the nation s food sector relies very heavily on imports, and the associated transport that brings them into the UK.
"Food produced on their own doorstep, using a system where animal and non-animal foods are symbiotic requires very little air travel, and makes excellent use of the resources our beautiful country provides. Foreign travel does not have the same necessity."
In addition, a report from a group of environmentally-minded business leaders has called on the government to show increased ambition and delivery of carbon-cutting policies to get the UK on track to meet climate goals.
It said there was an urgent need especially for policies to bring low-carbon heating to people s homes.