Dame Emma Thompson has warned that Britons face "crop failures and ruined lives" in a mock weather forecast at an Extinction Rebellion protest.
During the protest, the star warned people they face crop failures and may have to eat their own pets to survive.
Playing the role of a forecaster, she said in the video: "And now earth lovers, to the weather...
"For those of you expecting a habitable future, we have some pretty gloomy projections for you.
"Climate crisis trends show an increased chance of warmer, wetter winters and hotter, dryer summers, along with an increase of frequency and intensity of extremes.
"Better wrap up warm, stockpile food and remember there is a surprising amount of food in the average household pet.
"Looking ahead we are on course to sail past our 1.5 degree centigrade target putting us on track for long lasting and irreversible change."
Dame Thompson has previously taken part in Extinction Rebellion protests in London, flying back from Los Angeles to protest against damage to the environment.
She added on Thursday night: "General consensus does suggest there is an imminent crisis forecast, but not for politicians who seem to think this moist and fertile rain is ideal for growing an economy.
"As we move across the country, with severe flood warnings showing almost everywhere, and a thick fog covering Westminster, it is an uneasy picture."
She continued: "Expect crop failures, water contamination, damaged houses and ruined lives, and we will see these persistent weather fronts continue to wreck havoc across the nation, albeit with one or two days of dry and settled weather."
"Looking at the edges, we can see an estimated 3,000 kilometres of our coastline receding, although that is great news for the Tory heartlands, which will soon be expecting sea views encroaching across the hills," Dame Thompson said.
"All the signs are telling us to act now, but as our chief adviser King Canute once said, never let a rising tide get in the way of a good election."
The stunt was organised as part of the climate change protest group's 'Election Rebellion' demonstrations across the UK.
Around 20 protesters gathered outside Broadcasting House in Portland Place, holding a banner that read Tell The Truth.
Some were dressed in diving equipment to illustrate their claims of the threat of flooding in the UK in 2023.
Reading the forecast, Dame Thompson said: "Taking a closer look at London we see that 23 underground stations are at significant risk of flooding, with 57 at high risk.
"These climate trends could bring chaos to the inner city, but with underground drivers being retrained as gondoliers there are promising signs the economy will stay afloat. Thank you Boris."