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The Incredible Story Of How Climate Change Became Apocalyptic

Roger Pielke Jr, Forbes

The decision by the IPCC to center its fifth assessment report on its most extreme scenario has been incredibly consequential.

The rise of the new climate apocalysm can be traced directly to an consequential but little appreciated change in how the IPCC presents its scenarios. The consequences of this change have reverberated through the scientific community, media reporting, policy discussions and civic advocacy.

Almost two decades ago the IPCC developed a set of scenarios as the basis for integrating the work of its three working groups on science, impacts and mitigation. The scenarios were created to serve as the basis for projecting future climate change, the impacts of climate change and the consequences of mitigation action. Such coordination across the assessment work of the IPCC makes obvious sense.

At the time the IPCC recognized that “the future is inherently unpredictable and so views will differ as to which of the storylines and representative scenarios could be more or less likely. Therefore, the development of a single “best guess” or “business-as-usual” scenario is neither desirable nor possible.” Based on this perspective, the IPCC developed a set of scenarios for our collective futures but did not identify any of them as more probable than another, explaining that, “the term “business-as-usual” may be misleading” and “most climate scenarios considered in this report can be regarded as exploratory.”

The result of this approach was that projected futures in the absence of climate policies encompassed a very wide range of possible outcomes. The fourth assessment report of the IPCC published in 2007 acknowledged this wide range of futures, “There is still a large span of [carbon dioxide] emissions across baseline scenarios in the literature, with emissions in 2100 ranging from 10 GtCO2 [billion tons of carbon dioxide] to around 250 GtCO2.”

In other words, when it came to carbon dioxide emissions from the burning of fossil fuels and the associated climate consequences, the long-term future included possibilities that spanned from the highly optimistic (the 10 billion ton scenario) to the highly pessimistic (the 250 billion ton scenario), and everything in between. Climate change was not necessarily apocalyptic, but possibly could be if we made decisions leading to bad outcomes.

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