A leading climate scientist has said he is “very pessimistic” about the world reducing emissions to limit the global average temperature to 2C above pre-industrial levels.

Professor Robert Watson, of the Tyndall Centre for Climate Change, told the Today Programme that failure to do so will result in more heatwaves, floods, sea level rise, crop failure and health problems.

Almost every country on Earth signed up to the Paris Agreement in 2015 to limit global temperature rise to 1.5C but if not, at the very least 2C.

Eight years later, emissions continue to rise and current policies have us on track for around 2.5C of warming by the end of the century, according to Prof Watson.

We need to try and hold governments to start to act sensibly now and reduce emissions

Many countries including the UK have made pledges to go net zero – balancing the amount of greenhouse gases emitted into the atmosphere with those absorbed – but most are several decades away from achieving that.

The UK has committed to going net zero by 2050 but Prof Watson, who has been chairman of the Intergovernmental Panel on Climate Change and scientific adviser to the UK and US governments, said current emissions need to be slashed in half before 2030 to have any chance of reaching the Paris goals.

He said: “I think most people fear that if we give up on the 1.5C, which I do not believe we will achieve – in fact I’m very pessimistic about achieving even 2C – but if we allow the target to become looser and looser, higher and higher, governments will do even less in the future.

“We need to try and hold governments to start to act sensibly now and reduce emissions. But even governments with a really good target, like the United Kingdom, don’t have the policies in place, don’t have the financing in place to reach those goals.”

Scientists have warned that allowing the global average temperature to reach 1.5C could trigger irreversible tipping points that would heat the Earth beyond our control to unpredictable and dangerous levels.

Melting of polar glaciers and sea ice, die-back of the Amazon rainforest and coral reef extinction are all seen as being on the edge of tipping over into a feedback loop of self-destruction, whereby their decline itself becomes a source of warming.

The Earth has already warmed by around 1.2C, which has exacerbated heatwaves and wildfires that have caused thousands of deaths and millions of dollars of destruction and has led to the oceans heating to previously unseen levels.

Pascal Soriot, CEO of the pharmaceutical giant AstraZeneca, said seven million people are already being killed by climate change around the world – as many as those killed by Covid.

In response to a question about the economic impacts on people of cutting emissions rapidly, Prof Watson said: “It’s in their absolute best interest to tackle climate change, net zero by 2050, large reductions this decade.

“If we don’t, we’re going to see more heatwaves, more adverse effects on health, we’re going to see agriculture food production threatened, we’re going to see problems with water quantity and water quality.

“We’ll see more floods, more sea level rises displacing people on coastal areas, lots of adverse health effects.”

In a separate interview with the former BBC and now independent environment journalist Roger Harrabin, Prof Watson said current policies are “totally inadequate” and that world leaders had made a “terrible mistake” in prioritising inflation, the pandemic and the Ukraine war over the climate.

He also warned that the polar regions are melting faster than scientists predicted and that weather events, such as heatwaves and wildfires, have been much more devastating than previously thought.

“I am very concerned,” he said. “None of the observed changes so far are surprising. But they are more severe than we predicted. We probably underestimated the consequences.”