[altcognito]

It was based on co2 emissions doubling by 2050.

Though energy output has doubled, as a share coal has dropped in China and the US.

Wouldn’t you expect estimates based on difficult to predict human behavior to change based on new data?

[mc32]

Many people were saying that things were not as dire as they claimed. I’m glad they revised but you had silly people gluing themselves to thoroughfares (cars stuck in traffic waste more energy) and vandalizing what some people consider precious art and or national patrimony in the name of climate change thinking that those most dire predictions were indeed correct and we were all headed to hell in a hand basket.

[TheOtherHobbes]

Ruined cars piled up in streets waste even more energy - temporarily.

https://www.theguardian.com/world/2024/oct/31/why-were-the-f...

[DangitBobby]

So we are no longer worried about catastrophic or runaway climate change based on these revisions?

[magicalist]

> So we are no longer worried about catastrophic or runaway climate change based on these revisions?

Don't listen to mc32, they're intentionally confusing the issue. This is the paper they're presumably referencing from last month[1].

The IPCC reports are based on a number of carbon emissions scenarios based on how the world acts: how do countries coordinate, what are the mixes of new electricity generation that come online, how are old fossil fuel plants shut down, what cars are sold, etc. In their reports they simulate multiple scenarios to show what could happen depending on the choices made, since you can't really simulate policy decisions (like presidents paying companies billions to shut down wind projects), wars (ahem), and economic changes.

There were five main scenarios in the IPCC sixth report, from very low to very high GHG emissions.

What was "walked back" is not about climate simulation or feedback loops, but they've retired the very high emissions scenario they developed in the mid 2010s of a world that went all in on heavy economic growth all powered by fossil fuels and little effort toward electrification or decarbonization.

Basically based on renewable energy prices in the years since, electrification, etc, it's just not plausible that the world will grow in that way, so it's no longer worth trying to do simulations based on it.

Note that this was literally called the "very high emissions scenario" in the report, and that's there's still a "high" emissions scenario that will be included in the seventh IPCC report as an upper bound of plausible emissions. A couple of economic models already estimated that we'll likely emit less carbon than the new upper bound high emissions scenario, the same as it was for the very high scenario in the sixth report. Like then, though, it's still worth simulating because it is at least still plausible, and you never know how things will develop sociopolitically (this paper proposes six scenarios from very low to high and a new "high to low" scenario, see section 2.3) .

[1] https://gmd.copernicus.org/articles/19/2627/2026/

[mc32]

That’s tough to say. Weather systems are difficult to model. We have minimal understanding of the causes or inputs that control the very long climate cycles. Like we know that some day thousands of years from now we’ll have another unstoppable glacial period. We’ll also have a period free of polar ice. Those are cyclical and independent of CO2. We cannot stop either. We live in a very precious time.

I also think we should limit or be judicious as much as we can about what we pump into the atmosphere (or oceans or ground)

[Sabinus]

So the climate scientists of every government are lying? The calculations about how much heat is trapped by different CO2 amounts, bunk?