The Prince of Wales has warned the climate crisis will "dwarf" the impact of coronavirus.
In a recorded message, to be played at the virtual opening of Climate Week on Monday, Prince Charles said "swift and immediate action" was needed.
The prince said Covid-19 provided a "window of opportunity" to reset the economy for a more "sustainable and inclusive future".
He added that the pandemic was "a wake-up call we cannot ignore".
In his message, recorded from Birkhall in the grounds of Balmoral, Prince Charles said: "Without swift and immediate action, at an unprecedented pace and scale, we will miss the window of opportunity to 'reset' for... a more sustainable and inclusive future."
"[The environmental] crisis has been with us for far too many years - decried, denigrated and denied," he said.
"It is now rapidly becoming a comprehensive catastrophe that will dwarf the impact of the coronavirus pandemic."
Charles, 71, tested positive for coronavirus in March after displaying mild symptoms.
He has been championing environmental causes for decades and has previously called for members of the Commonwealth to work together to tackle climate change.
In January, he urged business and political leaders to embrace a sustainable future at the Davos summit, where he also met teenage climate activist Greta Thunberg.
The global lockdown led to a dramatic drop in greenhouse gases and air pollutants but a study last month suggested this would have a "negligible" impact on rising temperatures.
The analysis suggested that by 2030, global temperatures would only be 0.01C lower than expected.
But the researchers, led by the University of Leeds, stressed that a green recovery could significantly alter the long term outlook and keep the world from exceeding 1.5C of warming by the middle of this century.