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#ECS in the real world: Bengtsson and Schwartz 2013

29 Nov 2023 | Science Notes

In this week’s entry, the authors decided that, rather than try to estimate ECS itself, they would try to figure out the lower bound. Their primary focus was whether it was possible that extra CO2 in the air might lead to no warming at all or even cooling. Nope, said Lennart Bengtsson and Stephen Schwartz in their paper “Determination of a lower bound on Earth’s climate sensitivity”. At any rate the lowest plausible value of ECS seems to be positive at least to some degree. But along the way they also determined that the best estimate of ECS, based on real world observations, is about 2 degrees C, pretty much the same as all the other studies in this series. And a figure at which no significant policy to limit emissions does more good than harm.

Bengtsson and Schwartz began with the observation that, from what we know of the climate system, while the full adjustment to increased atmospheric CO2 takes centuries due to the slow overturning of ocean layers, most of the warming it causes (between 70% and 80% of it) happens over a decade or less. So using observations of temperature over the past few decades is not a bad way to proceed. And since the best and most comprehensive temperature coverage of the Earth only goes back to 1970, they limited their data collection to the 1970 to 2010 interval.

They also needed to estimate how much warming might have been concealed by the cooling effects of air pollution aerosols. Here they decided to assume that aerosol cooling hasn’t declined over the post-1970 interval, which deliberately biased their calculations towards the maximum possible sensitivity to warming from CO2. And when the data were all gathered and the computations done, they determined that the lower boundary figure, the number ECS was almost certainly above, was 1.16°C. But along the way they also got a best estimate for actual ECS of 2.0°C. And they noted that their estimate “coincides with the low end of the range for equilibrium climate sensitivity expressed as CO2 doubling temperature as given by the IPCC Assessment (Solomon et al., 2007).”

So yet again the IPCC range was plausible, but only the low end of it. This paper appeared in 2013, but the IPCC went right on peddling the idea that the best estimate is about 3C, and could be as high as 4.5 or 5C, based on how climate models behave.

Back in the real world, the data are stubbornly stuck at the low end of the range. According to their study, yes, CO2 warms the atmosphere. But not as much as most climate models say it will and not enough to worry about.

6 comments on “#ECS in the real world: Bengtsson and Schwartz 2013”

  1. The politically correct assumption is that all warming is due to man-made greenhouse gases, but this does rather beg the question of what caused the Medieval warm period, the Roman warm period and the Minoan warm period, to name only the most recent ones. So assuming that global temperatures go up and down for their own good reasons irrespective of anything the human race does, calculations of ECS are probably quite futile because the present slight warming may have little or nothing to do with human activities.

  2. 1-2-5C, all such estimates are just that, and the research above is simply correlation. "There has been this much warming so we will assign this much of it to co2", as they pull the dart out of the dart board. One guess is as good as the next.

  3. A cynical skeptic might assume that one of the parameters fed into the models propelling the mobile goalposts ("Do we all agree on limiting warming to 2deg?...Naaah, let's make it 1.5) is the flow of funding.
    Now lacking the energy to follow this epic as closely as before, I wonder whether water vapour, by far the dominant "greenhouse gas" (with an absorption spectrum overlapping CO2) is included in current models, or is it still left out because it is too difficult to measure?
    In a rare event, NASA finally admitted an error in assumption about the Amazon. The "lungs of the planet" do in fact act like mammalian lungs and exhale lots of CO2. When OCO2, the first successful attempt at global CO2 concentration mapping "to pinpoint the sources of pollution" launched in 2014, the radio silence about the results was puzzling until 2019 when NASA admitted, "We’re seeing that Earth’s tropical regions are a net source of carbon dioxide to the atmosphere, at least since 2009. This changes our understanding of things.” https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/
    This is hardly surprising since their guides for elementary teachers was to inform (scare?) the kids with, "CO2 is an invisible gas given off by dead animals and rotting vegetation", but a problem as Google routinely labels photos of white water vapour rising from cooling towers as "carbon pollution".

  4. "while the full adjustment to increased atmospheric CO2 takes centuries due to the slow overturning of ocean layers, most of the warming it causes (between 70% and 80% of it) happens over a decade or less" That is a rather simplistic assumption that greatly skews any conclusion. Or to put it in other words: How the *** do they know this? Wasn't there a study on here recently that shows NO causal relationship from CO2 to temperature, but quite a strong one in the other direction? It may have been on some other site, but it was pretty recent.
    That assumption '70-80% bla blah blah' is just that. Nothing in the data I have seen so far supports it.

  5. It is clear that CO2 has almost reached at saturation point at 300 parts per million. Beyond this increase any CO2 concentration will not lead to any warming. That's what the science says what kind of garbage do they have in these models because garbage and equals garbage out. These are nothing more than uncalibrated academic models with no predictive capability.

  6. Yes, I agree, CO2 has reached it max "damage' point.
    And even that was questionable.
    I love earth, I love humanity, Earth made us. Do we qualify as custodians of earth? Yes, we care in the west. And that is important.

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