Scientists have “retired” their worst-case-scenario predictions for climate change by 2100. Their paper argued that the RCP8.5 scenario is no longer worth considering.
RCP8.5 was the infamous 4.5 degrees warming scenario. It meant sea level rises of close to 1 metre and assumed carbon concentrations of 1,000 PPM, more than double the current ~430 PPM.
The recent paper drew attention because its authors included some of the same scientists involved in the Intergovernmental Panel of Climate Change (IPCC). In the period after the GFC and before #MeToo, IPCC forecasts were some of the biggest political issues of the time.
The climate forecasters now argue that the RCP8.5 is unrealistic given current trends. Specifically, the falling cost of renewable energy means there is no longer any reason to envision such a large growth in carbon emissions.
RCP 8.5 assumed a five-fold increase in coal consumption for the remainder of the century. This, among other factors, were forecast to lead to a tripling of carbon dioxide concentration in the atmosphere.
RCP8.5 was published in the lead-up to the Paris Climate Accord of 2015. Ironically, research suggests global coal consumption had already peaked in 2013.
This raises the question of how responsible the original publication was.
One scientist involved in the process stresses that climate research “is about understanding how Earth’s climate system behaves under certain conditions rather than a statement about what’s most likely to happen in the future.” In that sense, it was completely valid and indeed responsible to investigate upper-range scenarios.
However, RCP8.5 was often cited by media and advocates as the “business as usual” scenario. Whether motivated by political advocacy or just the quest for clicks, that’s the part where the truth was stretched. A 1-metre sea level rise being framed as business as usual helped fuel the apocalyptic mood around climate change in the 2010s.
The reality is that, politics aside, RCP8.5 is off the table because carbon power is losing the economic battle, and it will be technology and economics that shape the future. Yet on current trends, global temperatures are likely to rise by 2.5 degrees by 2100, exposing hundreds of millions more people to drought, heatwaves, floods and fire.
Feature image one of the tremendous climate graphics produced by @hausfath.
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