More than 100 world leaders representing over 85% of the planet's forests will commit on Tuesday to ending and reversing deforestation and land degradation by 2030, a British government statement says, in what would be the first substantial deal announced at the COP26 climate talks in Glasgow.

Among the nations taking part are Canada, Russia, Brazil, Colombia, Indonesia and the Democratic Republic of the Congo, all of which have significant tracts of forest. Brazil in particular has come under criticism for allowing an increase in the deforestation of the Amazon in recent years. The US and China will also be party to the agreement.

The deal is consequential to the climate as forests, when they are logged or degrade, emit carbon dioxide (CO2) into the atmosphere, accounting for around 11% of the world’s total CO2 emissions.

The leaders will make the announcement during a COP26 session about forests and commit £8.75 billion ($12 billion) of public funds to protection and restoration, alongside £5.3 billion ($7.2 billion) of private investment. CEOs from more than dozens of financial institutions, including Aviva, Schroders and Axa, are also committing to ending investment in activities that lead to deforestation.

“Today, at COP26, leaders have signed a landmark agreement to protect and restore the earth’s forests,” Johnson will say, according to the statement.

“These great teeming ecosystems — these cathedrals of nature – are the lungs of our planet. Forests support communities, livelihoods and food supply, and absorb the carbon we pump into the atmosphere. They are essential to our very survival.”

“With today’s unprecedented pledges, we will have a chance to end humanity’s long history as nature’s conqueror, and instead become its custodian.”

The agreement will likely provide a morale boost at COP26, which got off to shaky start after the G20 leaders’ summit in Rome over the weekend failed to result in an agreement on firm new climate commitments, particularly on when to end the use of coal.

It is also a breakthrough after years of negotiations on how to protect forests. There have been several different schemes to try and curb deforestation, including one that awarded credits to people conserving forests that could be traded on markets. These schemes often faced fierce opposition, particularly from Latin America, where indigenous groups and leaders said forests should be fully protected and not commodified.

“Indonesia is blessed as the most carbon rich country in the world on vast rainforests, mangroves, oceans and peatlands,” Indonesian President Joko Widodo said in a statement. “We are committed to protecting these critical carbon sinks and our natural capital for future generations.”

Rainforest Foundation Norway welcomed the deal, but said that funding should only be given to countries that showed results.

“This is the largest amount of forest funding ever pledged and it comes at a crucial time for the world’s rainforests. The new commitments have the potential to speed up necessary action from both governments and companies. We hope this funding will spur the political changes needed,” said Rainforest Foundation Norway Secretary General Toerris Jaeger in a statement.

“With big money comes big opportunities, but also great responsibilities. There is not time for baby-steps. Funding should therefore only reward real and substantial action taken by rainforest countries and those who respect the rights of Indigenous people and local communities.”

There are some reasons to be cautious, as several past forest protection schemes have come and gone.

In a years-long partnership, Norway agreed to transfer Indonesia $1 billion to put a moratorium on new logging permits. That deal fell apart recently, with Norwegian donors saying they did not see real results, while Indonesian officials complained the funds were not being transferred.