Several European leaders are set to speak at a UN, UK and France summit on climate.
UN secretary-general Antonio Guterres called on world leaders on Saturday to declare a climate emergency in their countries as the world faces a "catastrophic temperature rise".
"Can anybody still deny that we are facing a dramatic emergency?" Guterres said on the fifth anniversary of the signing of the Paris accord.
He said the commitments to keep the global temperature rise this century to below 2 degrees Celsius did not go far enough and are not being met: "Five years after Paris, we are still not going in the right direction".
It came as world leaders spoke in a virtual summit hosted by the United Nations, United Kingdom and France to mark the signing of the agreement.
The summit also comes a day after the European Union agreed to cut 55% of 1990 level greenhouse gas emissions by 2030, a move that environmentalists said did not go far enough.
German Chancellor Angela Merkel said, however, that she did not know what would have happened if European leaders attended the summit without an agreement on climate.
Several European leaders including Boris Johnson, Emmanuel Macron, Giuseppe Conte, Charles Michel and Ursula von der Leyen were also scheduled to speak at the summit.
Guterres criticised G20 countries for spending more than 50% of pandemic budgets on sectors "linked to fossil fuel production and consumption" instead of low carbon energy.
"We cannot use these resources to lock in policies that burden future generations with a mountain of debt on a broken planet," Guterres said, emphasising that there needed to be a global coalition on climate neutrality.
UK Prime Minister Boris Johnson, one of the co-hosts of the summit, said that the UK had already reduced its 1990 levels of greenhouse gas emissions by more than 40% and was committed to reducing emissions by 68% of 1990 levels in the next decade.
Johnson said that there would be millions of jobs created by green energy and that the UK would work to become a leader in wind energy.
The UK is set to host the UN climate change meeting in Glasgow next year.
French President Emmanuel Macron called on a transition to address inequalities and to be a "social transition" at the same time. He also said "welcome back" to the US and said he was looking forward to engaging with the new American administration on climate.
"We have the opportunity to build back greener and better," said Italian Prime Minister Giuseppe Conte, who added that "the impact of the pandemic on our social and economic system should not affect our determination to address these challenges...with longterm strategies".
Conte pledged to donate €30 million to the UN climate adaptation fund.
Chinese leader Xi Jinping said his country had worked to adopt the Paris agreement and repeated his measures. He said the country aimed to peak carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060.
Jinping said that China would lower carbon dioxide emissions per unit of GDP by over 65% from the 2005 level and increase the share of non-fossil fuels in primary energy consumption to around 25%, stating the country would promote "greener" social development.
China is currently the country with the highest level of greenhouse gas emissions.