Climate scientists have officially retired their worst-case scenario for global warming, but this is not the good news it might seem. The scenario, known as RCP 8.5, projected a temperature rise of about 4.5°C by the end of the century. However, it has become implausible due to falling renewable energy costs, climate policies, and emission trends.
Former editor of the Australian, Chris Mitchell, claimed this development dramatically cuts forecast warming. But this misrepresents the situation. While the worst-case scenario has been revised down, the best-case option is now also implausible because of slow action on emissions.
Dr Andrew King from the University of Melbourne, involved in recommending new scenarios, said: 'We have also dropped the most optimistic scenario for the 21st century with substantially higher peak warming in the new lowest emissions scenario than previously.'
The new worst-case scenario imagines a rollback of current mitigation policies, leading to about 3.5°C warming – still catastrophic. The Paris Agreement aimed to keep warming well below 2°C, ideally 1.5°C. The revised scenarios show that while we avoided the worst, we are not on track for the best.
Mitchell's claim that net-zero commitments were based on 'way off kilter' predictions ignores that these commitments were made to avoid 1.5-2°C warming, not 4.5°C. The real story is that both extremes are now off the table, leaving a middle path that still requires urgent action.
