The virtual event, co-hosted by the UN, Britain and France, aims to rally momentum and call for greater climate action.
Leaders from around the world are due to attend a day-long Climate Ambition Summit online, where they are due to present the progress they have been making and the plans they have to protect the environment.
The event, which aims to rally momentum and call for greater climate action, falls on the fifth anniversary of the Paris climate agreement, when nearly all countries pledged to limit global warming to well below 2 degrees Celsius above 1990 levels.
The summit, to be opened by British Prime Minister Boris Johnson at 14:00 GMT on Saturday and which will be live-streamed at climateambitionsummit2020.org, is being co-hosted by the United Nations, Britain and France, in partnership with Chile and Italy.
German Chancellor Angela Merkel is also due to attend and make a video statement.
China’s President Xi Jinping and France’s Emmanuel Macron are also among the heads of state taking part, with speaking slots handed to leaders of countries that submitted the most ambitious plans.
These include Honduras and Guatemala, both recently hit by devastating hurricanes, as well as India, which is battling increasingly erratic weather patterns and air pollution.
Business figures set to speak reportedly include Tim Cook, the chief executive of Apple, which has committed to making its whole supply chain carbon neutral by 2030.
But major economies including Australia, Brazil and South Africa are absent. Australia has not committed to net-zero emissions by 2050 and has been accused of setting targets that are too weak.
Meanwhile, more than 110 countries have committed to becoming carbon neutral by 2050.
China, the world’s biggest polluter, announced in September it plans to achieve net-zero emissions by 2060.
Unlike previous climate summits, no negotiations are planned. However, only those countries with climate policy achievements will be allowed to speak, creating a degree of pressure on the participants.
The annual UN international climate meeting was postponed due to the coronavirus pandemic. Britain was scheduled to host the event, known as COP26, in the Scottish city of Glasgow last month.
The summit – seen as one of the last chances to set the world on track to meet the Paris accord – will now take place in November 2021.
Governments at Saturday’s event are expected to come forward with several key plans: pathways to net-zero emissions; finance plans to support countries most vulnerable to climate effects; and policies to attain the 1.5C goal.
The summit comes as the UN warned this week that under current commitments, the Earth is still on course for a “catastrophic temperature rise” of more than 3C this century.
It warned this will create a crisis that will “dwarf the impacts of COVID-19” and has said current pledges to cut emissions to meet the Paris accord were “woefully inadequate”.
The United States, the world’s second-largest polluter after China, left the Paris agreement under President Donald Trump who questioned the accepted science behind climate change.
Incoming US climate envoy John Kerry plans immediately to re-enter the accord and President-elect Joe Biden has set a goal of carbon neutrality by 2050.
