A new study of an unusual type was published late last week. I think it is well worth reading and discussing, and hope its recommendations will be followed. The lead author is one Roger Pielke Jr., an environmental science professor who at one time developed a highly unfavorable reputation for downplaying the consequences of extreme carbon emissions. His work was at times quoted by advocates of climate change denial. This new work sort of follows that same line, but is now handled in a way that is easily justified. The old idea of “business as usual,” commonly employed as basis of future climate scenarios a decade ago, and still is today in RCP 8.5 scenarios, is in real life being overcome by astounding advances in renewable energy and its associated economies. Fossil fuel emissions growth, a key factor leading to future temperature increases, is better foreseen as unlikely to continue increasing at a rate that once seemed unstoppable.
Pielke and his co-authors manage to balance out this viewpoint with what amounts to an outright rejection of current ideas about what can realistically be accomplished on the low side—specifically holding increases within the UN’s target of 1.5C. The authors express a small hope of holding the increase to 2.0C by 2100 while leaving a range of 2 to 3C as a more practical end point—as advertised by the title of the study: “Plausible 2005-2050 emissions scenarios project between 2C and 3C of warming by 2100.” Open access is available at this link: https://iopscience.iop.org/article/10.1088/1748-9326/ac4ebf. The press release from the U of Colorado—https://phys.org/news/2022-02-paris-climate-agreement-goal.html—describes their position with this opening sentence, “The Paris Climate Agreement goal to limit global warming this century to 3.6 degrees Fahrenheit (2 degrees Celsius) over pre-industrial temperatures is still within reach, while apocalyptic, worst-case scenarios are no longer plausible, suggests a new CU Boulder analysis.”
The authors claim to have reviewed the content of a total of 1,311 climate scenarios that have been created around the world, and sorted out the findings, with this result: “The number of scenarios which most closely matched up to data from the past 15 years and subsequent emissions projections ranged from less than 100 to almost 500, depending upon the method applied. These scenarios represent what futures are plausible if current trends continue and countries adopt the climate policies they have already announced to reduce carbon emissions…..Why are these worst-case scenarios now less plausible? Mainly, they were all developed more than a decade ago, and a lot has happened since. For example, renewable energy has become more affordable and, thus, more common faster than expected…..Climate scenarios also tend to overestimate economic growth, especially in poorer countries…..It’s hard to overstate how much the [climate] research has focused on the four- and five- degree scenarios, RCP 8.5 being one of them. And those are looking less and less plausible by the year.”
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This is not mindless optimism by any means. I fully agree with the assessment as stated, while noting that it makes no attempt to evaluate a number of issues that have been set aside while awaiting additional study and resolution. From the news release, “Additional, more optimistic or pessimistic futures could also exist, the authors said.”
Carl