Scientists move away from 'worst-case' climate scenario as emissions growth slows

Climate scientists are increasingly moving away from using one of the most pessimistic global warming scenarios, arguing that current trends in renewable energy adoption, climate policies, and carbon emissions make the projection unlikely.

The scenario, known as RCP 8.5, has long been used by researchers to examine the potential consequences of very high greenhouse gas emissions.

It projected a world that could be 4.5-5C (8.1-9F) warmer than pre-industrial levels by 2100.

However, a recent scientific study concluded that the pathway has become increasingly improbable due to declining renewable energy costs, stronger climate policies, and slower growth in global carbon dioxide emissions, Norwegian broadcaster NRK reported on Tuesday.

"That's because green technology has taken off very well. Emissions are still increasing, but now they are increasing by perhaps up to 1 percent a year, compared to 3-4 percent a year, as they did in the early 2000s," climate scientist Bjorn Samset told the broadcaster.

He said future climate projections depend heavily on assumptions about human behavior and policy decisions.

"Maybe climate policy works very well and we cut emissions very quickly. Maybe climate policy doesn't work at all, there will be many big wars and the like. Then there will be very high emissions," Samset said.

Climate models are based on a range of possible futures, from rapid emissions reductions to scenarios where governments fail to curb greenhouse gas output.

According to Samset, RCP 8.5 is unlikely to play a major role in the next assessment report by the Intergovernmental Panel on Climate Change.

"Green technology has taken off very well. Emissions are still increasing, but now they are increasing by perhaps up to 1% a year, compared to 3–4% a year, as they did in the early 2000s. In that sense, the world is definitely doing well. It is a positive sign that it is now more relevant to think about the middle scenarios," he said.

Scientists also warn that uncertainty remains regarding how strongly the climate system responds to greenhouse gas emissions.

"One thing is how much we emit, another is how strongly the climate reacts to the emissions. There are some scientists who say that perhaps we have underestimated how strongly the climate is changing," Samset said.