The world is on course to crash through a dangerous warming threshold with key climate indicators shifting at an alarming rate, more than 60 top UN scientists have warned.

Bill Hare, CEO of think tank Climate Analytics, said Thursday it was "inevitable" that the world would breach the 1.5-degree Celsius (2.7 Fahrenheit) limit in around five years "unless emissions are reduced quickly."

"If emissions are reduced quickly, rapidly, as we know they can be, there is still a likelihood of exceeding a low overshoot of the 1.5 limit, and by low overshoot, I mean 1.6 degrees," he said during a press briefing at the UN interim climate negotiations in Bonn, Germany. 

Unless action is taken now, Hare added, it would not be long before the world also "bust through 2 degrees."

'We are already in crunch time'

The global surface temperature briefly exceeded the 1.5-degree limit in 2024, as greenhouse gas emissions from the burning of fossil fuels and deforestation hit a new high. Coal, oil and gas account for more than 80% of global energy consumption, despite increasing investment in renewable energy.

Scientists have said crossing the 1.5 limit, first set in the 2015 Paris climate agreement by nearly 200 nations, would see a rise in extreme heat waves, devastating droughts and more intense storms. That increase has already been felt in recent years.

The Indicators of Global Climate Change report, out Thursday, says that to have a 50% chance of staying under the threshold, the world can only release 130 billion tons of planet-heating carbon dioxide. At the current rate of CO2 emissions, however, that "carbon budget" will likely be spent by 2028.

"We are already in crunch time for these higher levels of warming," co-author Joeri Rogelj, a professor of climate science and policy at Imperial College London, told journalists, adding there was a "very high chance" that the world would "reach and even exceed 1.5 C." 

The report's authors said the findings should be taken as a reality check by global policymakers.

"I tend to be an optimistic person," said lead author Piers Forster, head of the University of Leeds Priestley Centre for Climate Futures in the UK. "But if you look at this year's update, things are all moving in the wrong direction."

Sea level rise has doubled

The report, a regular update between the landmark UN Intergovernmental Panel on Climate Change reports released every five to seven years, also highlighted other concerning key climate indicators. 

Sea level rise has doubled in recent years, up from around 1.8 millimeters per year between 1908 and 2018 to 4.3 mm since 2019, putting coastal cities and small island states at risk.

The Earth's energy imbalance, the difference between the amount of solar energy entering the atmosphere and the smaller amount leaving it, has nearly doubled in the last 20 years. Until now, 91% of human-caused warming has been absorbed by the oceans, but scientists said they don't know how much longer humanity can rely on them to soak up the excess heat.

Rogelj said actions moving forward now could still "critically change" the rate of warming and limit the increasingly destructive effects of climate change. 

"It's really the difference between just cruising through 1.5 C towards much higher levels of 2 C or trying to limit warming somewhere in the range of 1.5," he said.

Global conflict, Trump's policies weaken climate efforts

But action on that front has taken a hit, with global concerns shifting to security and other pressing matters amid multiple ongoing conflicts. Climate experts have pointed out that President Donald Trump's move to target climate action and pull the US out of the Paris agreement could also weaken international efforts to tackle the problem.

"You need everybody on board doing the right thing, and this is very difficult," said Brazilian climate secretary Andre Correa do Lago, president of the upcoming COP30 climate summit, speaking with DW before the report was released.

Ahead of the summit in November, countries are due to submit their so-called nationally-determined contributions, or NDCs, outlining how much they plan to reduce their domestic emissions by 2035. Until now, only 22 countries have presented their targets.

"Most scientists think that with the numbers that are to appear, we probably are going to surpass 1.5," Correa do Lago said. "Depending on the NDCs, we will be able to evaluate which is the path that we are following."

Louise Osborne contributed to reporting from the COP30 preparatory talks in Bonn, Germany.

Edited by: Tamsin Walker