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BAMOS May 2026
15 temperature outcomes – approaching 2 ° C between the most and least optimistic scenarios by 2100 – points to how much of the future is in our hands.
Why the fuss about RCP8.5?
The two previous releases included two closely related scenarios – RCP8.5 and SSP5-8.5 respectively.
Here,“ 8.5” refers to radiative forcing – the level of extra heat( in watts) trapped per square metre by 2100.
In these worst-case scenarios, the world sharply boosts fossil fuel use. Unsurprisingly, this leads to very high amounts of global warming. Scientists have long argued over whether this was plausible in the first place.
None of the new scenarios are as pessimistic as RCP8.5 / SSP5- 8.5. The worst possible scenario now envisions high emissions leading to warming of around 3.5 ° C by 2100. That would still be very, very bad.
Sceptics acting in bad faith
Climate sceptics leapt on the removal of RCP8.5 as a sign the projections were wrong. These attacks were not made in good faith, but to cast doubt on climate science.
A clear eyed assessment is that RCP8.5 was removed because climate action is starting to work.
But while the worst outcome has been averted, we have also missed the window for the best future climate.
The new scenarios have no pathway as optimistic as the lowest emissions scenario from the last round of major climate projections. That scenario – SSP1-1.9 – envisaged strong climate action and rapid cuts to emissions, leading to global warming peaking at around 1.5 ° C.
Because global emissions haven’ t yet begun to fall, the most optimistic new pathway would lead to warming peaking at about 1.9 ° C.
While we will definitely now pass 1.5 ° C, the hope is to only temporarily overshoot that level of warming while working to draw carbon dioxide back out of the atmosphere to get back to 1.5 ° C.
Our current emissions trajectory is somewhere in the middle – below the high emissions path but well above the most optimistic scenario. Based on current policies and countries’ actions, we’ re looking at around 2.6 ° C warming by 2100.
You might wonder why we need to keep redoing these climate scenarios.
One reason: facts change on the ground. Solar keeps rolling out far faster than expected, but fracking has opened up large new fossil fuel deposits. Political shifts make climate action more or less likely.
Another is because our climate models are continually improving. The better the models get, the more accurate and detailed our projections of sea level rise and other climate impacts can be.
Yes, this is progress
Taking RCP8.5 off the table is a sign of progress – we’ ve avoided the worst-case scenario. But we have also missed the best case future.
The next five years could play out in many different ways, leading to better or worse future climates. We must understand and prepare for what we’ re facing – and double down on our efforts to create the best future possible.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Celebrating the JSHESS award winners
Every year, JSHESS recognises the outstanding efforts of our Associate Editors, who are crucial in managing the review process and maintaining the high quality of the journal.
This year, the award was shared between two Associate Editors, Eun-Pa Lim and Brad Murphy( Bureau of Meteorology), for their exceptional contributions and dedication to the integrity of our peer-review process. Congratulations, Eun-Pa and Brad!
We also celebrate the important role of students in advancing both fundamental and applied oceanic and atmospheric science in the Southern Hemisphere. Each year, we award the best student-authored paper published in the journal.
This year’ s student award goes to Xiaoxuan Jiang for their study assessing a large set of CMIP6 models downscaled to regional climate models over the Australian CORDEX region, an impressive piece of work given the scale of the data involved and the clarity of its presentation. Congratulations, Xiaoxuan!
Paper: Jiang, X., Howard, E., Su, C.-H., Isphording, R. N., Ng, B., Chapman, S., Ji, F., Grose, M., Syktus, J., Trancoso, R., Thatcher, M., Narsey, S., Di Virgilio, G., & Kala, J.( 2025). Towards benchmarking the dynamically downscaled CMIP6 CORDEX-Australasia ensemble over Australia. Journal of Southern Hemisphere Earth Systems Science, 75, ES24050. https:// doi. org / 10.1071 / ES24050