"The continuation of our civilisations and the natural world upon which we depend, is in your hands", he said.
A goal of the two-week conference in Poland's southern coal mining region of Silesia is finalizing how governments report on their efforts to reduce greenhouse gas emissions and keep global warming within the limits of the Paris climate deal.
The organisers called for ambitious climate policies to limit global warming to 1.5 degrees Celsius in line with goals set by the Paris Agreement in 2015.
The opening ceremony could not have been more dramatic as Attenborough warned that climate change is a man-made disaster on a global scale.
The World Bank Group said Monday it is doubling funding for poor countries preparing for climate change to $200 billion over five years.
The climate rules and policies that are agreed at the worldwide and national levels will have an enormous impact on how business can help combat climate change, affecting companies' domestic and global operations, supply chains, planning and investments.
A failure to mitigate the impacts of climate change would wreak catastrophic damage on things we all share -our common planet and the prospects for future generations. The only holdout was the United States, which announced under President Donald Trump that it was withdrawing from the climate pact. Greta Thunberg said world leaders who skip the climate summit are "very irresponsible".
Stating that we "are extremely concerned about the climate crisis" Fijian Prime Minister Frank Bainimarama issued a joint statement, together with three other former COP Presidents, last night calling on countries to send an unequivocal message from COP24 in Katowice, Poland, that they are serious about strengthening their commitments to reduce emissions and help build resilience.
"We have a collective responsibility to invest in averting global climate chaos", he said.
Four former leaders of United Nations talks, including Laurent Fabius of France, who led negotiations for the Paris agreement, issued a statement urging immediate action.
He told parties to the UN Climate Change Convention (UNFCCC) that the world could not afford to waste any more time before taking action on climate change.
Attenborough, known for hosting nature broadcasts including the popular BBC series "Planet Earth", was chosen for the UN's "people's seat", representing those populations most affected by climate change.
Waskow, who has followed climate talks for years, said despite the Trump administration's refusal to back this global effort the momentum is going in the right direction.
Citing various alarming UN reports including one on rising global Carbon dioxide emissions and another one on increasing greenhouse gas concentrations in the atmosphere he called on nations to pay attention to the science and step up their pace as well as their ambitions.
The UN chief thanked Modi for his commitment to increase India's nationally determined contributions to the Paris Agreement.
ASSOCIATED PRESS Prime Minister of Fiji, Frank Bainimarama, addresses representatives of nearly 200 nations during a ceremonial opening of the key U.N. climate conference.
"These guidelines need to push countries to immediately cut emissions to achieve the 1.5°C temperature goal and to deal with growing climate impacts".