This weekend my beautiful Brighton constituency was even more stunning than usual. The sun was sparkling on the sea and families were picnicking by the shore. It could have been a lovely early summer day – but this was February, and it was impossible to shake the feeling that something wasn’t right.

Yesterday the unseasonable weather continued – as temperatures topped 20C for the first time ever in winter. Those of us fighting for climate action often lambast sceptics and fossil-fuel executives for suggesting cold weather “proves” everything is fine – and scientists avoid drawing direct links between climate and weather. But this warm spell cannot be dismissed as a one-off. This is part of a wider global trend of record-breaking temperatures and increasingly extreme weather patterns – and it’s about time politicians and the media acknowledged that.

Nine of the 10 hottest years on record have occurred since 2005. January 2019 was Australia’s hottest month ever – with averages topping 30C in a deadly heatwave. Prolonged droughts worsened California’s destructive wildfires.

This is what climate breakdown looks like. It’s not a sudden change or a single dramatic event like in a Hollywood disaster movie. It’s the steady creep of weird weather onto the news agenda, and the gradual shift in our perceptions of what’s normal.

Last year’s three-month heatwave meant England had the hottest summer on record – and it was joint-hottest for the whole of the UK. Record numbers of people visited A&E, and crops like potatoes were severely affected.

This season's record heat vs the same time last year Show all 8 1 /8 This season's record heat vs the same time last year This season's record heat vs the same time last year Top: people walking their dogs on Blyth Beach in Northumberland on February 27 2018 Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: Edinburgh's High Street on March 1 2018 Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: the Croft An Righ in Holyrood, Edinburgh on February 28 2018 Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: Victor the polar bear at the Yorkshire Wildlife Park in Doncaster on February 28 2018 Bottom: polar bears Pixel and Nissan at the same park on February 26 2019 PA This season's record heat vs the same time last year Top: cars stuck on the M80 near Haggs in Glasgow on February 28 2018. Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: the Kelpies in Helix Park, Falkirk on February 28 2018 Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: the M876 in Scotland on March 03 2018 Bottom: the same view on February 26 2019 PA This season's record heat vs the same time last year Top: the Kelpies in Helix Park, Falkirk on February 28 2018 Bottom: the same view on February 26 2019 PA

And the scary thing is, this is just the start. Human activity has already made the world warmer by 1C – but scientists warn we have already “locked in” another 0.5C, and a major UN report suggests we have just 11 years to take bold action to prevent temperatures escalating beyond 1.5C.

If we fail, things will get unimaginably worse. If we reach 2C, coral reefs will be all but wiped out, an additional 411 million people will suffer from water scarcity, and yields of key crops will suffer. At 3C, each drought in Africa could last five years, and the Mediterranean could see 38 nights a year when the temperature fails to drop below 20C. Warming of 4C compared with pre-industrial levels would see sea levels rise by up to a metre, and global conflict and warfare could double.

Young people who face growing up in this apocalyptic world understand this. But they’re not willing to stand by as their futures become kindling for the bonfire that is our current economic system.

Earlier this month, young people across the country went on school strike to demand the government declare a climate emergency and take action to prevent climate catastrophe. It was one of the most inspirational and hopeful acts I’ve seen in years.

These brave young people are demanding a voice. They want the voting age to be lowered to 16 because they understand that democracy is a vital part of climate justice. They will live longest with the consequences of decisions made now, so it’s only right that they should have a say in shaping them.

But everyone deserves more of a say over our shared future. Faced with this unprecedented challenge, we need new ways of making decisions – like citizens’ assemblies, which bring together representative groups of people to consider objective evidence and make recommendations to politicians.

We also urgently need a green new deal – a massive transformation of our economy, mobilising resources on a scale unprecedented in peace time, with huge investment in clean energy, warm homes and affordable public transport, designed to offer a green job to everyone who wants one and restore hope and meaningful work to communities hollowed out by years of deindustrialisation and austerity.

Investment on this scale will allow us to explore a new economic model – designed to improve life for everyone while protecting the natural environment we depend on, and measuring our success by people’s wellbeing instead of company profits. If we’re going to secure our future, we need to reimagine our present.

Winter heatwaves are disconcerting, and the threat of worse to come can be terrifying – but I take huge hope from the rising tide of activism. It’s going to take all of us to force global governments to embrace radical change. So if sunbathing in February doesn’t feel right to you, get out onto the streets instead.