More than 100 global leaders have pledged to halt and reverse deforestation and land degradation by the end of the decade, underpinned by $US19 billion ($A25 billion) in public and private funds to invest in protecting and restoring forests.
The joint statement at the COP26 climate talks in Glasgow was backed by the leaders of countries including Brazil, Indonesia and the Democratic Republic of Congo, which collectively account for 85 per cent of the world's forests.
The Glasgow Leaders' Declaration on Forest and Land Use will cover forests totalling almost 34 million square kilometres, according to a statement from the UK prime minister's office on behalf of the leaders.
"We will have a chance to end humanity's long history as nature's conqueror, and instead become its custodian," said British leader Boris Johnson, calling it an unprecedented agreement.
A slew of additional government and private initiatives were launched on Tuesday to help reach that goal, including billions in pledges for indigenous guardians of the forest and sustainable agriculture.
Forests absorb roughly 30 per cent of carbon dioxide emissions, according to the non-profit World Resources Institute. The forests take the emissions out of the atmosphere and prevent them warming the climate.
Yet this natural climate buffer is rapidly disappearing. The world lost 258,000 square kilometres of forest in 2020, according to WRI's deforestation tracking initiative Global Forest Watch - an area larger than the United Kingdom.
Monday's agreement vastly expands a similar commitment made by 40 countries as part of the 2014 New York Declaration of Forests and goes further than ever before in laying out the resources to reach that goal.
Under the agreement, 12 countries including Britain have pledged to provide $US12 billion of public funding between 2021 and 2025 to help developing countries, including in efforts to restore degraded land and tackle wildfires.
At least a further $US7 billion would be provided by more than 30 private sector investors.
Five countries, including the Britain and United States, and a group of global charities on Tuesday also pledged to provide $US1.7 billion in financing to support Indigenous people's conservation of forests and to strengthen their land rights.
Environmentalists say Indigenous communities are the best protectors of the forest, often against violent encroachment of loggers and land grabbers.