IPCC sixth assessment - five scenarios

[Richard Kerver]

Please memorize these five scenarios embodied in the IPCC’s sixth assessment report.  The first installment is now official.  It focuses on the physical science behind climate change, and considers five scenarios that game out how humanity will respond, or not, to the specter of warming.  Knowing this brief gist will help foster the necessary continuing dialog which must ensue.

1) SSP1-1.9  — This scenario has been described as “taking the green road.” It’s the most ambitious and hardest-to-achieve storyline. It envisions a gradual but concerted shift toward clean energy, with few political barriers in adapting to and mitigating climate change. This entails a rapid drawdown of fossil fuels, widespread deployment of clean energy, increasing energy efficiency, and lower resource demands. By the middle of the century, humanity will zero out its contributions to climate change.

2) SSP1-2.6  — This pathway envisions that the world will eventually get its act together on climate change, but more slowly than in the optimistic path of SSP1-1.9. It envisions an economy with net-zero emissions after 2050. SSP1-2.6 also expects the global population to reach 7 billion people. The result is a world that will warm up to 1.8°C, with a likely range between 1.3°C and 2.4°C by 2100.

3) SSP2-4.5  — Sometimes described as “middle of the road,” this scenario lines up with what countries have pledged to do so far about climate change. If every country actually fulfilled its existing obligations, their emissions would lead to about 2.7°C of warming by 2100, with a likely range between 2.1°C and 3.5°C. Under this scenario, the Arctic Ocean would likely be ice-free in the summer, which could have ripple effects on weather all over the world.

4) SSP3-7.0 — In this narrative, nationalism is resurgent and countries retreat from international cooperation, focusing instead on their own economic goals. “I sort of jokingly refer to this as Trumpworld,” said Zeke Hausfather, director of climate and energy at the Breakthrough Institute and a contributing author to the latest IPCC report. “It’s a reasonable storyline for what a worst-case world could look like.”

5) SSP5-8.5 — Imagine a world where humanity doesn’t just do nothing about climate change but continues to make it worse. This scenario envisions global economic growth across the board fueled by burning coal, oil, and natural gas, with the planet’s population leveling off at 7 billion people. While resources are devoted to adapting to climate change, there is little effort to mitigate emissions.

Note:  We're on the last path that leads to scenario SSP5-8.5.  The Biosphere - Life on Eaarth - can only persist if temperatures are stabilized below 2.0°C.  

Reference:  https://www.vox.com/22620706/climate-change-ipcc-report-2021-ssp-scenario-future-warming