Climate change planning has become one of the most important and contentious public policy issues of our time. Communities are being asked to make decisions that affect homes, infrastructure, insurance, property values and future development. Those decisions deserve to be based on the best available science – and an honest understanding of what that science is telling us.
In climate science, there are very few people better placed to explain the purpose and appropriate use of emissions scenarios than Professor Detlef van Vuuren. Professor van Vuuren is not simply another climate scientist commenting on RCP8.5 – he created that emissions scenario framework that governments, policymakers and scientists around the world have relied upon for more than a decade and is used by the Intergovernmental Panel on Climate Change (IPCC).
If anyone understands what RCP8.5 was intended to represent, how it should be used and whether it remains plausible today, it is Professor van Vuuren.
That is why his recent interview with Alistair Harding is so important.
For years, RCP8.5 has often been described as a “business-as-usual” scenario – a future in which humanity simply continues its current path. Professor van Vuuren makes it clear that this is a misunderstanding.
RCP8.5 was developed as an extreme emissions pathway. It assumed not only that the world would fail to implement meaningful climate policies, but also that several unfavourable global trends would occur simultaneously. It was never intended to represent the most likely future.
Importantly, Professor van Vuuren explained that when scientists describe RCP8.5 as “implausible”, they are referring to the emissions trajectory itself. Advances in technology, the rapid growth of renewable energy and lower-than-expected coal consumption have made that pathway increasingly unlikely.
That does not mean climate change has gone away or that long-term risks should be ignored. Quite the opposite. Climate science remains an essential tool for helping societies prepare for future risks. But climate scenarios are exactly that – scenarios. They are not planning tools – not predictions of what will inevitably happen.
Perhaps the most important lesson from the interview is that good climate planning requires proportionality.
Professor van Vuuren emphasised that governments should consider “the right range of possible futures”, including worst-case outcomes where appropriate. Planning exclusively for best-case scenarios would be irresponsible. Equally, planning exclusively for worst-case scenarios can lead to poor and disproportionate policy outcomes.
The planning horizon matters. A billion-dollar piece of infrastructure designed to last 100 years may justify consideration of extreme scenarios. A decision that affects a homeowner's ability to build, insure or sell their property today raises a very different set of considerations.
He also stated that it would be “completely unfair” if highly uncertain and distant projections were used to substantially determine the value of someone’s property today.
That observation deserves serious attention. Most homeowners do not own property on a 125-year planning horizon. Their mortgages are measured in decades, not centuries. It is entirely reasonable to ask whether highly uncertain worst-case projections extending well beyond our lifetimes should carry the same weight as more immediate and plausible risks when making today’s planning decisions.
Climate science does not support choosing a single extreme scenario and applying it universally. It supports considering a range of plausible futures, understanding the uncertainties involved and making proportionate decisions that reflect the risks being assessed.
The lesson from this interview is neither to minimise climate risks nor to exaggerate them. It is to use climate science responsibly.
Communities deserve planning that is scientifically robust, legally defensible and fair. Worst-case scenarios have an important place in risk management, but they should remain what they were always intended to be – tools for stress-testing our decisions, not default assumptions about our future.
Good climate planning is neither alarmist nor complacent: it is evidence-based, continually evolving and grounded in uncertainty, requiring decision-makers to weigh the full range of plausible futures and make choices that are proportionate to the risks communities face today and tomorrow.
This article was originally published by RCR Media.
