New targets to eliminate the gases driving climate change from Wales' economy and way of life are to become law.
The Welsh Government said "business as usual" was no longer an option.
Changing weather patterns are already "wreaking havoc" and acting now is "the right thing to do for our children and grandchildren", it says.
The move brings Wales into line with the UK push for "net zero emissions" by 2050.
However, environment minister Lesley Griffiths said she wanted to "get there sooner".
It will mean huge upheaval - from replacing hundreds of thousands of gas boilers in people's homes, to potentially finding new ways of making steel at Port Talbot without burning coal.
But the process will lead to new green jobs, and improvements to people's health while meeting international obligations to try and avoid a dangerous rise in global temperatures, the government said.
It will publish a revised action plan ahead of the major UN climate change conference - COP26 - in Glasgow later this year.
Advisers at the independent Climate Change Committee (CCC) have already warned Wales is not on track to meet existing, less stringent goals to slash emissions.
By 2018 - the latest year for which data is available - Wales had seen a 31% fall in greenhouse gas emissions compared with 1990 levels.
New legal targets will force a 63% reduction by 2030 and 89% by 2040, with Wales reaching 'net zero' - effectively a 100% cut - by 2050.
'2020s a crucial decade'
Any gases still produced then would need to be very limited and strictly managed - for example, they would need to be entirely soaked back through carbon capture technologies, trees or peatbogs.
The government said it was accepting the recommendations made by the CCC in a report to Welsh ministers in December.
It had described the 2020s as a "crucial decade" if targets were to be achieved.
The advisers said a net zero Wales was possible with action on uptake of low-carbon vehicles and boilers, while industry in south Wales needed to work together to move away from fossil fuels or install carbon capture and storage technology by the mid 2030s.
Low carbon electricity generation needed to shift from 27% now to 100% by 2035, and buildings better insulated so less power was used and wasted.
By 2030, 43,000 hectares of mixed woodland must be planted, the advisers said, increasing to 180,000 hectares by 2050 - to soak up emissions.
Action was needed at both a UK and Welsh government level, according to the CCC.
Nick Pidgeon, professor of environmental psychology at Cardiff University, said the announcement was "hugely significant".
Industry, transport, housing and agriculture were all big contributors to Welsh emissions, he said, and would require "sustained attention over the next few years".
"And it needs to start now - although we think about the 2050 target... greenhouse gas emissions stay up in the atmosphere for a long time," he said.
"So, the sooner you start on that journey to net zero the better - because you will then be putting less up over the next 20 to 30 years."
Biologist and broadcaster Lizzie Daly told BBC Radio Wales that reducing carbon emissions was "one of the biggest challenges of our time".
She said: "A lot of our land in Wales is farmland, so working with people who have that land and use it to create better environmental outcomes is crucial.
"We need to see bigger changes in our transport around cities, Cardiff and Swansea are doing lots to help minimise the impact of vehicle emissions and help with air quality.
"If we are to meet these goals we have to get a move on."
Ms Griffiths said the global climate outlook was "grave", and "as with Covid, climate change will impact us all, but the stark reality remains that our most vulnerable communities will be hit the hardest."
"Through Covid we have shown a Team Wales effort that has saved lives and protected our NHS, and I am calling on everyone to use the same spirit to build the Wales we want for our future generations."
Plaid Cymru's shadow minister, Delyth Jewell, said the party would implement a £6bn "green economic stimulus" if it gains a majority in this year's Senedd elections.
She said: "To tackle climate change we have to be ambitious. It's been two years since the Welsh Government declared a climate emergency but empty words have been followed by little action."
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