Short Takes: The evidence accumulates that the "Climate Sensitivity" estimate in our models is BADLY off.
Short Takes: The evidence accumulates that the "Climate Sensitivity" estimate in our models is BADLY off.
On new papers
A new paper, "A 485-million-year history of Earth’s surface temperature" dropped today. It's NOT good news.
A 485-million-year history of Earth’s surface temperature.
Science, 20 Sep 2024, Vol 385, Issue 6715, DOI: 10.1126/science.adk3705
It has been written up already by WAPO and the NYT.
An effort to understand Earth’s past climates uncovered a history of wild temperature shifts and offered a warning on the consequences of human-caused warming.
Prehistoric Earth Was Very Hot. That Offers Clues About Future Earth. - NYT 9/19/24
At times during the past half-billion years, carbon dioxide warmed our planet more than previously thought, according to a new reconstruction of Earth’s deep past.
From the paper:
Understanding how global mean surface temperature (GMST) has varied over the past half-billion years, a time in which evolutionary patterns of flora and fauna have had such an important influence on the evolution of climate, is essential for understanding the processes driving climate over that interval. Judd et al. present a record of GMST over the past 485 million years that they constructed by combining proxy data with climate modeling (see the Perspective by Mills). They found that GMST varied over a range from 11° to 36°C, with an “apparent” climate sensitivity of ∼8°C, about two to three times what it is today.
Although several Phanerozoic (the last 539 million years) temperature reconstructions exist, during the intensively studied Cenozoic Era (the last 66 million years), they are colder and less variable than individual estimates from key time periods, particularly during ice-free (greenhouse) intervals. This discrepancy suggests that existing Phanerozoic temperature records may underestimate past temperature change
There is a strong relationship between PhanDA GMST and CO2, indicating that CO2 is the dominant control on Phanerozoic climate. The consistency of this relationship is surprising because on this timescale, we expect solar luminosity to influence climate. We hypothesize that changes in planetary albedo and other greenhouse gases (e.g., methane) helped compensate for the increasing solar luminosity through time.
The GMST-CO2 relationship indicates a notably constant “apparent” Earth system sensitivity (i.e., the temperature response to a doubling of CO2, including fast and slow feedbacks) of ∼8°C, with no detectable dependence on whether the climate is warm or cold.
--------------
Here's the current best "estimates" of 2XCO2 by the models of the Moderates in Climate Science.
An Assessment of Earth’s Climate Sensitivity Using Multiple Lines of Evidence — Dec 2020
Here’s the best answer as of December 2020.
+2.6–3.9°C — 66%
+2.3–4.5°C — 95%
+2.0–5.7°C — 05%
Which says, that at CO2 levels of 560ppm there is a:
95% chance that the Global Mean Temperature (GMT) will increase at least +2.3°C and possibly as much as +4.5°C.
66% chance that the GMT increase will be between +2.6°C and +3.9°C.
05% chance that the GMT could increase as much as +5.7°C.
Moderates — +2.6°C up to +3.9°C.
Alarmists — +4.5°C up to +5.7°C.
The paleoclimate data STRONGLY supports the Alarmist position although the Moderate models assign it a "less than" 5% likelihood.
This new analysis indicates that 560ppm might actually be around +8°C hotter than our 1850 baseline.
It adds support for a value of around +8°C that was proposed in this paper.
Cenozoic evolution of deep ocean temperature from clumped isotope thermometry :
Science/30 Jun 2022/Vol 377, Issue 6601 pp. 86–90/DOI: 10.1126/science.abk0604
Strongly suggesting that the Moderate estimates for "Climate Sensitivity" are about 100% too LOW.
This is Collapse related because James Hansen thinks we are at 535ppm(e) thanks to CH4 (methane). The implications are, that we are going to experience RAPID and EXTREME WARMING up to +8°C by 2100.
WAPO got a Moderate to comment on the paper.
Michael Mann, a climate scientist at the University of Pennsylvania who is known for his analyses of past global temperatures, said he was also surprised by the suggestion that the planet got so warm.
The finding supports many scientists’ concern that feedback loops in the Earth system could lead to much higher temperatures than most climate models predict, he wrote in an email. But it’s also possible that the data assimilation assumes too much warming and is missing factors that might forestall a runaway greenhouse effect.
“While I applaud the authors for this ambitious and thoughtful study, I am skeptical about the specific, quantitative conclusions,” Mann said.
So, nothing to worry about.
RIGHT?
I’ll be coming back to this. It integrates really well with the picture that the new crop of papers is painting about how the Climate System actually works.
-rc
09/19/2024
I'm in the KISS club: keep it simple stupid club. I prefer hard science data driven over speculations over millions of years in the past. So, I go with C3S and their data indicates that we are seeing a 0.2 degC increase annually, so, at this rate, 1 degC increase every 5 yrs. Go to their "climate pulse" page and see for yourself. The "canary in the coal mine" for me is the 1.2 trillion tons of global ice melting annually, 3.3 billion tons per day, 41 million tons PER HOUR. Any fool can see the worldwide climate collapse on the news. The fossil fuel lobby does a great, if unethical, job of obscuring the truth for mass consumption. The simple truth is that too many humans are using too many natural resources and producing too much pollution, including heat. Enjoy the entertaining speculations of the "experts" if you wish, but I grew-up watching ole Joe Friday: "just the facts, mam".
Thanks for the update. One thing I would ask though is, what does the paleoclimate record indicate, if anything, about the PACE of change? The paleoclimate record, going back millions of years, cannot be very precise in terms of time interval. Even data points every hundred thousand years would be considered extremely fine detail when you're operating on that scale. And timing is everything in terms of impact to human civilization.
It's certainly possible that increasing CO2 concentrations to 560 will result in a +8C change in temperature relative to 1850. But the real question is, how LONG does that transition take? If it takes place over a century, yeah, that is beyond catastrophic for our civilization. Like, "a few millions people surviving as hunter gatherers circa 2150" bad.
However, if it takes 10,000 years for those changes to slowly heat up the planet, well we could probably adapt to even a change that large on that type of time scale. On a long enough time scale, you don't even need to abandon and relocate buildings and cities; those things don't last that long anyway. And on that timescale, large scale atmospheric carbon capture really would seem practical. But even if not, you could end up with humanity slowly transitioning to high-latitude regions.
I'm really curious what we can say about the rate of change. Because it is really what is critical here. If we've set in motion a process that will cause the climate to reach +8C 10,000 years from now, well that really isn't actually much of a problem. Removing CO2 from the atmosphere in bulk by the end of this century is dubious. Doing it slowly over millennia, as our tech and capabilities continue to advance? That's quite doable. Hell, at that timescale, even sci fi solutions like big orbital mirrors become quite plausible. On that scale, even a +8C problem becomes something we can manage quite easily.
I would think that all that the paleoclimate data would tell us is that EVENTUALLY we would end up at the +8C level. But on a long enough time scale, we can adapt to damn near anything. The real crucial question for us and our civilization isn't the absolute amount of change, but the rate of change. We can trivially handle +8C over the next 10k years. Over the next hundred? We're completely screwed.