A new 66 million-year history of carbon dioxide offers little comfort for today (we're screwed)

[NickB79]

Last edited Fri Dec 8, 2023, 07:22 AM - Edit history (1)

Mainstream estimates indicate that on scales of decades to centuries, every doubling of atmospheric CO2 will drive average global temperatures 1.5 to 4.5° Celsius (2.7 to 8.1° Fahrenheit) higher. However, at least one recent widely read study argues that the current consensus underestimates planetary sensitivity, putting it at 3.6 to 6°C of warming per doubling.

Snip

The consortium's members did not collect new data; rather, they came together to sort through published studies to assess their reliability, based on evolving knowledge. They excluded some that that they found outdated or incomplete in the light of new findings, and recalibrated others to account for the latest analytical techniques. Then they calculated a new 66-million-year curve of CO2 versus temperatures based on all the evidence so far, coming to a consensus on what they call "Earth system sensitivity." By this measure, they say, a doubling of CO2 is predicted to warm the planet a whopping 5 to 8° C.

Edit: here's the link, sorry!

https://phys.org/news/2023-12-million-year-history-carbon-dioxide-comfort.amp

[2naSalit]

1. We've already blasted through...

The first five years of that ten year window of opportunity.

[Simeon Salus]

2. It's been too late for quite some time now

?si=GTGY8mBA7plNkx6P

[OKIsItJustMe]

3. NewScientist: Ancient climate analysis suggests CO2 causes more warming than thought

Ancient climate analysis suggests CO2 causes more warming than thought

A reconstruction of 66 million years of climate history indicates global temperature may be even more sensitive to carbon dioxide levels than current models estimate
By Alison George

7 December 2023

It is possibly the toughest question in climate science: how much warming does carbon dioxide cause? A new analysis of 66 million years of Earth’s climate history suggests the planet is much more sensitive to greenhouse gases than current climate models predict – meaning we could get far more warming in the long term.

…

There is a big caveat, however. This new insight into Earth’s deep climate history covers trends over hundreds of thousands of years, not the shorter timescales of decades or centuries that are pertinent to humans today, so it doesn’t tell us what global temperatures are likely to be in 2100. “There’s a sluggish, cascading effect that slowly kicks in,” says Hoenisch.

The vast timescales covered in the study also mean it can’t detect the finer details of climate sensitivity. Michael Mann at the University of Pennsylvania says the climate sensitivity may have been different at other times in Earth’s history compared with now, and this probably explains why the study arrived at a higher estimate than those based on more recent periods.

“In short, the estimates of climate sensitivity from this study are probably not applicable to current human-caused warming,” says Mann. “Nonetheless, the study confirms the very close relationship between CO2 and global temperatures, underscoring the threat of continued fossil fuel burning.”

http://www.science.org/doi/10.1126/science.adi5177

[ancianita]

4. Thank you. The OP neglected to provide the link.

[littlemissmartypants]

5. Link?

[OKIsItJustMe]

6. Link & Excerpt

A New 66 Million-Year History of Carbon Dioxide Offers Little Comfort for Today

A Massive Study Sharpens the Outlook on Greenhouse Gases and Climate

BY KEVIN KRAJICK |DECEMBER 7, 2023

A massive new review of ancient atmospheric carbon-dioxide levels and corresponding temperatures lays out a daunting picture of where the Earth’s climate may be headed. The study covers geologic records spanning the past 66 million years, putting present-day concentrations into context with deep time. Among other things, it indicates that the last time atmospheric carbon dioxide consistently reached today’s human-driven levels was 14 million years ago—much longer ago than some existing assessments indicate. It asserts that long-term climate is highly sensitive to greenhouse gas, with cascading effects that may evolve over many millennia.

The study was assembled over seven years by a consortium of more than 80 researchers from 16 nations. It appears today in the journal Science.

“We have long known that adding CO2 to our atmosphere raises the temperature,” said Bärbel Hönisch, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory, who coordinated the consortium. “This study gives us a much more robust idea of how sensitive the climate is over long time scales.

Mainstream estimates indicate that on scales of decades to centuries, every doubling of atmospheric CO2 will drive average global temperatures 1.5 to 4.5 degrees Celsius (2.7 to 8.1 Fahrenheit) higher. However, at least one recent widely read study argues that the current consensus underestimates planetary sensitivity, putting it at 3.6 to 6 C degrees of warming per doubling. In any case, given current trends, all estimates put the planet perilously close to or beyond the 2 degrees warming that could be reached this century, and which many scientists agree we must avoid if at all possible.

…

[C Moon]

7. By no means a scientist, just a stupid person wondering: if the temp gets to a certain degree...

and the ocean waters increase, could that increase cloud cover, rain and cooling?
Kind of a mini ice age?

By that time, we'd be gone. And "mother nature" would have done what needed.

[OKIsItJustMe]

8. Not a stupid question at all

The net influence of clouds and water vapor is one which has left many scientists uncertain.

Here’s a bit from the recent paper by Hansen et al (I have added emphasis):

https://doi.org/10.1093/oxfclm/kgad008

…

ECS defined by Charney is a gedanken concept that helps us study the effect of human-made and natural climate forcings. If knowledge of ECS were based only on models, it would be difficult to narrow the range of estimated climate sensitivity—or have confidence in any range—because we do not know how well feedbacks are modeled or if the models include all significant real-world feedbacks. Cloud and aerosol interactions are complex, e.g. and even small cloud changes can have a large effect. Thus, data on Earth’s paleoclimate history are essential, allowing us to compare different climate states, knowing that all feedbacks operated.

…

Earth’s surface change is the other forcing needed to evaluate ECS: (1) change of surface albedo (reflectivity) and topography by ice sheets, (2) vegetation change, e.g. boreal forests replaced by brighter tundra, and (3) continental shelves exposed by lower sea level. Forcing by all three can be evaluated at once with a GCM. Accuracy requires realistic clouds, which shield the surface. Clouds are the most uncertain feedback [52]. Evaluation is ideal for CMIP [53] (Coupled Model Intercomparison Project) collaboration with PMIP [54] (Paleoclimate Modelling Intercomparison Project); a study of LGM surface forcing could aid GCM development and assessment of climate sensitivity. Sherwood et al. [21] review studies of LGM ice sheet forcing and settle on 3.2 ± 0.7 W/ m², the same as IPCC AR4 [55]. However, some GCMs yield efficacies as low as ~0.75 [56] or even ~0.5 [57], likely due to cloud shielding. We found [7] a forcing of –0.9 W/m² for LGM vegetation by using the Koppen [58] scheme to relate vegetation to local climate, but we thought the model effect was exaggerated as real-world forests tends to shake off snow albedo effects. Kohler et al. [59] estimate a continental shelf forcing of −0.67 W/m². Based on an earlier study [60] (hereafter Target CO₂), our estimate of LGM-Holocene surface forcing is 3.5 ± 1 W/m². Thus, LGM (1821 kyBP) cooling of 7°C relative to mid-Holocene (7 kyBP), GHG forcing of 2.25 W/m², and surface forcing of 3.5 W/m² yield an initial ECS estimate 7/(2.25 + 3.5) = 1.22°C per W/m². We discuss uncertainties in Equilibrium climate sensitivity section.

…

So, let’s think through your question. If the temperature gets high enough, would that produce more clouds, causing cooling? Perhaps, but then, the presumed cooling would mean less evaporation, and fewer clouds. (Right?) So, it wouldn’t cause more cooling overall, it would just tend to act as a sort of moderator on the warming. (See what I’m saying?)

If you watch your local TV weather forecast, they may mention that since it is a cloudy night, it won’t be as cold, because the clouds act like an insulating blanket at night, keeping the ground warmer. This is what makes the influence of clouds so confusing. On the one hand, they reflect sunlight back into space (meaning less warming) while, at the same time, they help to trap heat.

Although it doesn’t get as much publicity as CO₂, “water vapor” is also a powerful greenhouse gas.

Here’s another excerpt:

…

Climate response time
In this section we define response functions for global temperature and Earth’s energy imbalance that help reveal the physics of climate change. Cloud feedbacks amplify climate sensitivity and thus increase eventual heat uptake by the ocean, but cloud feedbacks also have the potential to buffer the rate at which the ocean takes up heat, thus increasing climate response time.

…

So, the clouds slow down the rate of warming, but they don’t reverse it, instead, over time, they tend to increase it.

As for you claiming to be “stupid,” I used to try to reassure people, “You’re not stupid, you’re ignorant. Ignorance I can help with. — I can’t do much for stupidity.”

I encourage you to read the paper.

[C Moon]

10. Wow. Awesome. Thanks. That makes complete sense.

[OKIsItJustMe]

11. You're welcome.

I try to make sense. Sometimes I succeed!

[Think. Again.]

9. K&R