CO2 emissions on track to push Earth beyond 1.5 degree threshold by 2028, report finds.

Humans are releasing so much greenhouse gas that within three years, planet Earth will likely be unable to avoid 1.5 degrees Celsius of long-term warming since pre-industrial times.  That's the finding of a new study published in the Earth System Science Data journal on Wednesday.

That 1.5 degree goal, established by the 2015 Paris agreement, has been a cornerstone of international efforts to curb worsening climate change. Scientists say crossing that limit would mean worse heatwaves and droughts, bigger storms and rising sea levels.

Joeri Rogelj is a Climate Scientist at Imperial College London and co-author of the new study:

“At 1.5 or at 2 degrees [Celsius], we now expect higher risks to ecosystems, to poor populations, for tipping points to happen, and for extreme events to happen. So, we expect them to happen at lower levels of warming compared to the evidence and the scientific knowledge we had at the time of the Paris Agreement.” 

Researchers say humans can release only 130 billion more metric tons of CO2 before the 1.5 limit becomes inevitable, and we’re on track to reach that by early 2028.  

“Within three years," Rogelj says, "we will have emitted the remaining carbon budget for limiting warming to 1.5 degrees [Celsius] with at least a 50 percent chance. So that means if we emit more, there is only lower chances than 1 in 2 that warming will be kept to 1.5 degrees [Celsius].” 

Earth's energy imbalance

The report shows that the rate of human-caused warming per decade has increased .27 degrees Celsius per decade. And the imbalance between the heat Earth absorbs from the sun and the amount it radiates out to space, a key climate change signal, is accelerating, the report said. 

The increase in emissions from fossil fuel burning is the main driver. But reduced particle pollution, which includes soot and smog, is another factor because those particles had a cooling effect that masked even more warming from appearing, scientists said. Changes in clouds also factor in. That all shows up in Earth’s energy imbalance, which is now 25 percent higher than it was just a decade or so ago, experts said.

'A clear political limit'

The planet temporarily passed the key 1.5 limit last year. The world hit 1.52 degrees Celsius (2.74 degrees Fahrenheit) of warming since pre-industrial times for an entire year in 2024, but the Paris threshold is meant to be measured over a longer period, usually considered 20 years. Still, the globe could reach that long-term threshold in the next few years even if individual years haven't consistently hit that mark, because of how the Earth's carbon cycle works.

That 1.5 degree threshold is “a clear limit, a political limit for which countries have decided that beyond which the impact of climate change would be unacceptable to their societies,” said Rogelj, a climate scientist at Imperial College London.

Once that mark is crossed, many small island nations could eventually disappear because of sea level rise, and scientific evidence shows that impacts become particularly extreme beyond that level, especially hurting poor and vulnerable populations, Rogelj said. He added that efforts to curb emissions and the impacts of climate change must continue even if the 1.5 degree threshold is exceeded.