Worst-Case Climate Change Scenarios Are Highly Implausible, Argues New Study

David Wallace Wells, the author of Living on an uninhabitable planet: After global warming (2019) warned, “The UN says we’re on track to get to about 4 degrees or 4.3 degrees of warming by the end of the century if we continue as we are.” Perhaps you recall Gaia Vincent, an author, stating in 2019, The GuardianGlobal heating of 4C in 2100 by experts is considered a realistic possibility.

You might consider reviewing the latest study from the University of Colorado Climate Change Policy Researcher Roger Pielke. It confirms the August 2021 findings of the Intergovernmental Panel on Climate Change, which states that although the future climate will likely be more extreme, that it won’t be catastrophically warm, this is not the case.

Based on future scenarios in which agricultural and fossil fuel emissions would increase atmospheric carbon dioxide by nearly 1,400ppm (ppm) over the next century, these dire predictions are sadly accurate. At the moment, atmospheric carbon dioxide has risen to just under 420ppm from 280ppm in pre-industrial times. Largely as a result of this increase in atmospheric concentrations of greenhouse gases, global average temperature has risen to around 1.1°C above the pre-industrial level.

Climate scientists called this the worst case scenario RCP8.5. It was updated by the Sixth Assessment Report of the Intergovernmental Panel of Climate Change (IPCC AR6), which examines the science base of climate change. The new name of SSP5-8 has also been given to it.

In its August 2021 AR6 report, the IPCC acknowledged that there is a low likelihood of scenarios like RCP8.5 and SSP5-8.5 due to recent changes in energy.

According to the AR6 Report, recent events in the energy sector indicate that global fossil fuel use is expected to remain flat for at least the next 50 year. One of the main ways that the RCP8.5 scenario goes off the rails of plausibility is that it projects a six-fold rise in global coal consumption per capita by 2100. Global carbon dioxide emissions in the future will not rise or fall as much as they did under medium RCP4.5, SCP6.0, and SSP2-4.5 scenarios.

Roger Pielke, Jr., University of Colorado Climate Change Policy Researcher, has pointed out for many years that the growth of the global economy will not trace the emissions pathways that have led to the most dire outcomes. However, people who predict dire climate catastrophe by the year 2025 are relying on RCP8.5 climate scenarios.

Pielke has published with his collaborators a new study in The Journal Environmental Research Letters that argues that these intermediate emissions scenarios are much more plausible than the high end scenarios that engendered fears of climate catastrophe. These scenarios show warming between 2 and 3°C by 2100. The median is 2.2 degrees C. These scenarios, however, do acknowledge the fact that there is no way to limit 21st-century global warming below 1.5 degrees Celsius.

These calculations use the latest projections of energy demand and policy based on information from the International Energy Agency. World Energy Outlook report. According to the report, world coal consumption is expected to peak this decade rather than rising sixfold. On the other hand, the U.S. Energy Information Administration projects that world coal consumption will continue to rise slightly through 2050, but that’s still far from the sixfold increase entailed in the RCP8.5 scenario.

Pielke and colleagues asked Pielke which scenarios had projected CO2 emissions growth errors or divergences less than 0.1% per annum over observed growth rates for 2005 to 2020 in order to assess their plausibility. This is how did the scenarios track what has actually been happening with carbon dioxide over the past fifteen years. The next step is to analyze the ability of the scenarios to track carbon dioxide emissions, starting at 2005. Next comes the analysis using the IEA’s projected future emissions until 2050.

This chart shows the plausibleness of different IPCC emission scenarios. It tracks how closely they correspond to expected cumulative carbon dioxide emissions over the next century. Blue dots (0.1%) and triangles (0.3%) are given to scenarios that most closely match projected and actual IEA emission. Pielke explained that all possible scenarios are available in Substack’s newsletter. The honest brokerAccording to the report, we “aim for less than three degrees Celsius of total warming in 2100.” Actually, the median projection calls for 2100 degrees Celsius warming. He says that this is “inspitting distance to the Paris Agreement goal of keeping temperatures at 2.0 degrees Celsius”.

Under the 2015 Paris Climate Change Agreement, signatories committed to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels.”

So man-made global warming of 4°C by 2100 above pre-industrial levels is not a real possibility.

Pielke questions, “Is there good news for climate change?” We are.