Their report found that 20 of the 35 planetary vital signs they use to track the climate crisis are at record extremes. As well as greenhouse gas emissions, global temperature and sea level rise, the indicators also include human and livestock population numbers.
Many climate records were broken by enormous margins in 2023, including global air temperature, ocean temperature and Antarctic sea ice extent, the researchers said. The highest monthly surface temperature ever recorded was in July and was probably the hottest the planet has been in 100,000 years.
The scientists also highlighted an extraordinary wildfire season in Canada that produced unprecedented carbon dioxide emissions. These totalled 1bn tonnes of CO2, equivalent to the entire annual output of Japan, the world’s fifth biggest polluter. They said the huge area burned could indicate a tipping point into a new fire regime.
The researchers urged a transition to a global economy that prioritised human wellbeing and cut the overconsumption and excessive emissions of the rich. The top 10% of emitters were responsible for almost 50% of global emissions in 2019, they said.
Dr Christopher Wolf, at Oregon State University (OSU) in the US and a lead author of the report, said: “Without actions that address the root problem of humanity taking more from Earth than it can safely give, we’re on our way to the potential collapse of natural and socioeconomic systems and a world with unbearable heat and shortages of food and freshwater.
“By 2100, as many as 3 billion to 6 billion people may find themselves outside Earth’s livable regions, meaning they will be encountering severe heat, limited food availability and elevated mortality rates.”
The analysis, published in the journal Bioscience, is an update of a 2019 report that has been endorsed by 15,000 scientists.
“For several decades, scientists have consistently warned of a future marked by extreme climatic conditions caused by ongoing human activities,” the report says. “Unfortunately, time is up… we are pushing our planetary systems into dangerous instability.”
The scientists said: “We are shocked by the ferocity of the extreme weather events in 2023, [which caused] profoundly distressing scenes of suffering to unfold. We are afraid of the uncharted territory that we have now entered.”
The report highlighted severe flooding in China and India, extreme heatwaves in the US and an exceptionally intense Mediterranean storm led to the deaths of thousands of people in Libya.
The report said that by mid-September, there had been 38 days with global average temperatures more than 1.5C above pre-industrial levels, which is the world’s long-term goal for limiting the climate crisis. Until this year, such days were a rarity, the researchers said.
Other policies recommended by the scientists included phasing out fossil fuel subsidies, ramping up forest protection, a shift towards plant-based diets in wealthy countries and adopting international treaties to end new coal projects and phase out oil and gas.
“We also call to stabilise and gradually decrease the human population with gender justice through voluntary family planning and by supporting women’s and girls’ education and rights, which reduces fertility rates,” they said.
In September, a different analysis of the Earth system using nine planetary boundaries concluded that this planet’s life support systems had been so damaged that Earth was “well outside the safe operating space for humanity”. The planetary boundaries are the limits of key global systems – such as climate, water and wildlife diversity – beyond which their ability to maintain a healthy planet is in danger of failing.