50th Anniversary of First Climate Model. Spoiler, They Got it Right.

May 19, 2018

Climate science is built on first order physics, and reliable observations of past climate – not models.

The adage “Every model is wrong, but some models are useful” applies, but nevertheless, looking back at the earliest attempts at modeling the atmosphere with modern computers, we can now make a judgement on climate science’s accuracy.

Above, archival footage of scientists predicting in the 1980s changes that had not yet been observed, versus current obs.
Below, Andy Dessler and others on why Dilbert, among others, don’t understand climate models and climate science.

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Astrophysicist Ethan Siegel in Forbes:

Modeling the Earth’s climate is one of the most daunting, complicated tasks out there. If only we were more like the Moon, things would be easy. The Moon has no atmosphere, no oceans, no icecaps, no seasons, and no complicated flora and fauna to get in the way of simple radiative physics. No wonder it’s so challenging to model! In fact, if you google “climate models wrong“, eight of the first tenresults showcase failure. But headlines are never as reliable as going to the scientific source itself, and the ultimate source, in this case, is the first accurate climate model ever: by Syukuro Manabe and Richard T. Wetherald. 50 years after their groundbreaking 1967 paper, the science can be robustly evaluated, and they got almost everything exactly right.

If there were no atmosphere on Earth, calculating the climate would be easy. The Sun emits radiation, the Earth absorbs some of the incident radiation and reflects the rest, then the Earth re-radiates away that energy. Temperatures would be easily calculable based on albedo (i.e., reflectivity), the angle of the surface to the Sun, the length/duration of the day, and the efficiency of how it re-radiates that energy. If we were to strip the atmosphere away entirely, our planet’s typical temperature would be 255 Kelvin (-18 °C / 0 °F), which is most definitely colder than what we observe. In fact, it’s about 33 °C (59 °F) colder than what we see, and what we need to account for that difference is an accurate climate model.

The number one contributor, by far, to this difference? The atmosphere. This “blanket-like” effect of the gases in our atmosphere was first discovered nearly two centuries ago by Joseph Fourier and worked out in detail by Svante Arrhenius in 1896. Each of the gases present has some amount of absorptive effects in the infrared portion of the spectrum, which is the portion where Earth re-radiates most of its energy. Nitrogen and oxygen are terrible absorbers, but good ones include water vapor, methane, nitrous oxide, ozone and carbon dioxide. When we add (or take away) more of those gases from our planet’s atmosphere, it’s like thickening (or thinning) the blanket that the planet wears. This, too, was worked out by Arrhenius over 100 years ago.

But a true climate model is more complex, because there’s more at play than just the atmosphere. The oceans ensure that the amount of water vapor (and cloud cover, which impacts temperature significantly) change dependent on conditions, and if you tinker with one component of the atmosphere — like carbon dioxide, for instance — it impacts the concentrations of other components. Scientists refer to this general process as feedback, and it’s one of the largest uncertainties in climate modeling.

The big advance of Manabe and Wetherald’s work was to model not just the feedbacks but the interrelationships between the different components that contribute to the Earth’s temperature. As the atmospheric contents change, so do both the absolute and relative humidity, which impacts cloud cover, water vapor content and cycling/convection of the atmosphere. What they found is that if you start with a stable initial state — roughly what Earth experienced for thousands of years prior to the start of the industrial revolution — you can tinker with one component (like CO2) and model how everything else evolves.

The title of their paper, Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity (full download for free here), describes their big advances: they were able to quantify the interrelationships between various contributing factors to the atmosphere, including temperature/humidity variations, and how that impacts the equilibrium temperature of Earth. Their major result, from 1967?

According to our estimate, a doubling of the CO2 content in the atmosphere has the effect of raising the temperature of the atmosphere (whose relative humidity is fixed) by about 2 °C.

What we’ve seen from the pre-industrial revolution until today matches that extremely well. We haven’t doubled CO2, but we have increased it by about 50%. Temperatures, going back to the first measurements of accurate global temperatures in the 1880s, have increased by nearly (but not quite) 1 °C.

In 2015, all the coordinating lead authors, lead authors and review editors on the last Intergovernmental Panel on Climate Change (IPCC) report were asked to nominate their most influential climate change papers of all time. The 1967 paper by Manabe and Wetherald received eight nominations; no other paper received more than three. The uncertainties surrounding climate sensitivity are still grappled with today, of course, but these were laid out and quantified fifty years ago, and the analysis is still both valid and valuable today. It takes into account clouds, aerosols, stratospheric cooling, water vapor feedback and atmospheric emissions.

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9 Responses to “50th Anniversary of First Climate Model. Spoiler, They Got it Right.”

  1. Sir Charles Says:

    Amazing enough to read that in Forbes.

  2. J4Zonian Says:

    The Forbes article was nice. It would have been even better 20 years ago. The fact that this information is considered news to the readers of Forbes–among the richest, supposedly most connected and informed people on the planet–is astounding and deeply disturbing. No surprise at all, but disturbing. We all know how far behind every other developed country in the world the US is (except Russia). But it’s hell being reminded so often how screwed we are unless the sane people of the US pretty much stage a revolution and take over the country.

    • rhymeswithgoalie Says:

      I started reading The Economist around the late 80s/early 90s, and was pretty impressed with the science writing they had, especially compared to all of the other general news/politics newspapers and magazines. I later learned that The Economist, rather than hiring a journalist for the science beat and teaching them science, they had hired a *scientist* and taught him journalism. Those were the days.

      Meanwhile, I have noticed some improvement in medical reporting at the BBC. When interviewing a medical researcher, the reporter always makes it a point to ask how likely and/or how long until it could be turned into a practical treatment, if ever, and allows the researcher temper the expectations of the listening public.

  3. MorinMoss Says:

    I must make a gif of Sara Myhre shaking her head in disbelief

  4. Glenn Martin Says:

    Anyone have any idea how Dilbert creator Scott Adams got the idea that climate models are somehow dependant on economic models? I’ve never heard that idea elsewhere. Is it some particular website he’s been visiting?


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