The Green Party will pledge to invest £100bn a year in climate action for a decade if it gets into power.
Launching her campaign in Bristol, co-leader Sian Berry will say: “Some things are even bigger than Brexit. This must be the climate election.”
The party says it will fund the pledge by borrowing £91.2bn a year, with a further £9bn from “tax changes” including a rise in corporation tax.
The Greens will also set out plans to make Britain carbon neutral by 2030.
Political parties have begun to launch their election campaigns after the overnight dissolution of Parliament heralded the official start to the five-week campaign period.
Brexit is set to be a crucial issue when voters go to the polls on 12 December, with Prime Minister Boris Johnson insisting the UK will leave in January if he is returned to power.
However, some parties, including the Greens, are using their campaigns to draw attention to other issues.
Elsewhere in the election campaign on Wednesday:
- Boris Johnson is due to start the Conservative Party election campaign at a rally in the West Midlands and will say only his party can “get Brexit done”
- In a speech in Telford, Labour leader Jeremy Corbyn will say his government should be judged on the “real change” it delivers and “the concrete improvements it makes to the lives of millions”
At the Green Party election campaign launch, Ms Berry is due to say: “Let’s be honest about the situation we’re in. We know these are dark times. It’s easy to fear the future.
“The threat of Brexit hangs over our heads, the climate emergency rages from the Amazon to the Arctic, and our fragile democracy is under attack.
“But despite all this, Greens don’t fear the future.
“We welcome the future. Because we know that we stand at the threshold of what could be the most exciting and prosperous period of British history.”
Reality Check: Where will the £100bn come from?
By Tom Edgington, BBC Reality Check
The Green Party is proposing to fund its key pledge by increasing government borrowing by £91bn a year.
The remaining £9bn will come from tax changes, including an increase in corporation tax to 24%.
This would represent a massive increase on current borrowing levels. The independent Institute for Fiscal Studies believes government borrowing will be £55bn this year.
In terms of how £100bn compares to other areas of UK government spending, it’s about the same that’s spent on education each year.
Deputy leader Amelia Womack will also set out the Green Party’s plan to make the country carbon neutral by 2030.
This will be done, Ms Womack will say, by building 100,000 energy efficient homes each year, by “revolutionising” transport infrastructure, a roll-out of renewable energy and creating “hundreds of thousands” of “low carbon jobs” – including, for example, workers installing insulation in homes.
“This could be our last chance to elect a Parliament to keep us below dangerous warming,” Ms Womack will say.
“The climate doesn’t care about promises. The environment doesn’t care about pledges.
“What we need is action. And the Green Party has the single most ambitious and comprehensive plan to go carbon neutral by 2030 while delivering social justice across Britain.”
Labour has also set out some of its own environmental pledges, including a promise to cut UK carbon emissions by 10% through a home improvement programme.
A Labour government would fund £60bn of energy-saving upgrades, such as loft insulation, enhanced double glazing and new heating systems, by 2030.
The Conservatives say it has “a proper plan to continue reducing carbon emissions” which will build on the “400,000 low carbon jobs we’ve already created [while in government]”.