Carbon emission cuts need to be about 80 per cent more ambitious to stay below 2 degree Celsius global warming -- considered a threshold for climate stability and climate-related risks such as excessive heat, drought, extreme weather and sea level rise -- a new study says.
The scientists, including those from the University of Washington in the US, used statistical tools to reevaluate the cuts in carbon emissions that would be needed globally to stay below the 2 degree target proposed in the Paris Agreement international climate treaty.
According to the study, published in the journal Communications Earth and Environment, an average of 1.8 per cent drop in emissions per year rather than the previously agreed 1 per cent per year, would be required to stay within the 2 degree threshold.
"To have an even chance of staying below 2 degrees Celsius, the average rate of decline in emissions would need to increase from the 1 per cent per year needed to meet the nationally determined contributions, to 1.8 per cent per year," the scientists wrote in the study.
In the research, the scientists used the same statistical approach to model the three main drivers of human-produced greenhouse gases -- national population, gross domestic product per person, and the amount of carbon emitted for each dollar of economic activity, known as carbon intensity.
"A number of people have been saying, particularly in the past few years, that the emissions targets need to be more ambitious. We went beyond that to ask in a more precise way: How much more ambitious do they need to be?" said study lead author Adrian Raftery from the University of Washington in the US.
The analysis revealed a range of likely future outcomes based on data and projections so far.
Even with updated methods and five more years of data, the conclusion remained similar to the previous estimates: Meeting Paris Agreement targets would give only a 5 per cent probability of staying below 2 degrees Celsius warming.
Since climate policies may not targeting population growth or economic growth, the researchers calculated what change in the "carbon intensity" measure could likely be needed to meet the 2 degrees warming goal.
They now believe increasing the overall targets to cut carbon emissions by an average of 1.8 per cent annually, as opposed to 1 per cent, and continuing on that path after the Paris Agreement expires in 2030, would give the planet a 50 per cent chance of staying below 2 degrees warming by 2100.
"Achieving the Paris Agreement's temperature goals is something we're not on target to do now, but it wouldn't take that much extra to do it," said study first author Peiran Liu from the University of Washington.
"Globally, the temperature goal requires an 80 per cent boost in the annual rate of emissions decline compared to the Paris Agreement, but if a country has finished most of its promised mitigation measures, then the extra decline required now will be smaller," Liu said.
The scientists also estimated how much more each country needed to increase its target -- known as nationally determined contributions (NDCs) -- in order to lower its emissions by 80 per cent.
"For the largest emitters, the needed increases in the NDCs would be 7 per cent for China, 38 per cent for the US, 55 per cent for India, 49 per cent for Japan, and 25 per cent for Germany," the scientists wrote in the study.
They also suggested that countries increase their accountability by reviewing progress annually, rather than on the five-year, 10-year, or longer timescales included in many existing climate plans.
"To some extent, the discourse around climate has been: 'We have to completely change our lifestyles and everything,'" Raftery said.
"The idea from our work is that actually, what's required is not easy, but it's quantifiable. Reducing global emissions by 1.8 per cent per year is a goal that's not astronomical," he added.