The Climate According to Numbers

on The Physical Science Basis

Jun 16, 2024

A little while ago I took us up to outer space to help us see the Earth, the living surprise of it among it’s lifeless neighbors. I wanted to show how rare our climate is, not collapsed at physical, redundant equilibrium like the others, but dynamically upheld by living systems within a range of conditions congenial to life. I pointed out how this life creates processes the others lack, like transpirational cooling, biotic cloud generation, the terrestrial recycling of rain, and the surface roughness of the land’s vegetation. To that we could add living soil, capable of banking both water and carbon, the essential ingredients of climate, and also add ecosystems, interwoven with living beings and processes that maintain flows of water, energy and nutrients. Then I pointed out what seems like an anomaly, that the science for understanding this rather life-inspired climate declares a “physical science basis.”

I remember the first time I noticed those words. I had recently heard the late Spanish meteorologist, Millan Millan, describe his two-legged understanding of human-caused climate change, with one leg for carbon emissions and the greenhouse effect and another leg for land degradation and water cycle effects. Apparently, it was a fairly traditional perspective, as Millan didn’t invent it but observed it when he helped edit what is perhaps the first global report on climate change, the 1971 book Inadvertent Climate Modification: Report of the Study of Man’s Impact on Climate. I purchased the book and confirmed the land leg for myself in an extensive section titled “Climate Effects of Man-Made Surface Change.” Why don’t we know this? I wondered. As I researched the web looking for clues, the 2015 IPCC Assessment Report, AR5, popped up on the screen with title Global Climate Change 2015: The Physical Science Basis. I suddenly saw, after years of climate activism, those last four words. Could they have something to do with it?

It’s clearly important. The IPCC modifies the titles of all their assessment reports with it, and of its three Working Groups, Working Group I, which produces the assessments, is titled The Physical Science Basis. Yet I’ve never encountered any attempt, either from the IPCC reports or from climate journalists, to define the term or explain its use. That’s what we’re going to try to do here, discern what the term means, where it comes from and why it’s used.

Interestingly enough, the earliest written reference I’ve found for the term is in the book Millan helped edit, in a chapter subsection called “The Physical and Mathematical Basis of Climate Theory,” which asserts that all variables affecting climate can be mathematically reduced to the basic laws of physics. The atmosphere, for instance, is governed by Newton’s second law of motion; conservation of mass; the first law of thermodynamics; the laws of radiative transfer; the principles of diffusion and thermodynamics of water vapor. It may seem like a lot of Greek to most people, but by reducing the atmosphere to physical laws, and performing the necessary equations, it’s behavior can be mathematically modelled and predicted. The same thing is assumed for all other climate variables, with an equation-set for each. It requires a huge amount of number crunching, but computers were making it feasible, bringing into view the possibility of “a quantitative and complete mathematical description” of the Earth’s climate.

That possibility was taken up three years later, in the spring of 1973, when a London session of the Global Atmospheric Research Program (GARP) proposed the “organization of an international study conference on the physical basis of climate and climate modelling,” which convened in the summer of 1974 outside Stockholm, Sweden. There about 70 scientists met to “determine the potential of mathematical calculation for predicting and explaining the climate quantitatively,” producing a report in 1975 entitled The Physical Basis of Climate and Climate Modelling, concluding “prospects are good that mathematical models will provide an understanding of the basic controls of the climate which will prove essential for the future management of the natural resources of the earth.”

The US Committee of GARP, through the National Science Administration, produced another report that same year, Understanding Climate Change: A Program for Action, that went further, calling for just such an effort. They began by stating the problem. “Unfortunately, we do not have a good quantitative understanding of our climate machine and what determines its course. Without this fundamental understanding, it does not seem possible to predict climate—neither in its short-term variations nor in its larger long-term changes.” But as mentioned, rapidly increasing computing speeds were bringing this possibility into range, and they pointed to satellites, which “allow us to monitor those parameters that we now believe control the climate machine: the and sun’s output, the earth’s albedo, the distribution of clouds, the fields of ice snow, and the temperatures of the upper layers of the ocean.” “There is a new generation of atmospheric scientists,” they stated confidently. “Their tools are the computer, numerical models, and satellites, and they know how to use them well.”

Some things can be said about the language being used, the frequent reference to the climate as a “machine,” for instance. Machine seems a better metaphor for the Earth’s purely physical neighbors, like mars and the moon. And it should be noted that of “those parameters that…control the climate machine,” living processes were not included. We are getting a sense now of the world the physical science basis emerged from, that of atmospheric science and organizations such as the Global Atmospheric Research Program. It’s a very physical, mathematical world because the atmosphere, its subject, is very physical, and therefore readily subject to mathematical reduction. Accordingly, CO2, well dispersed in that atmosphere, is also readily reduced mathematically.

The early 70’s was a heady time for atmospheric science. Computers had delivered vast new capabilities for atmospheric modelling and GARP was a key player in those efforts. Originally set up in 1967 to extend “the range of large-scale weather forecasts beyond the then limit of three to five days,” the assumption was that what worked for weather prediction could be extended for the purposes of climate prediction. From the Understanding Climate Change forward: “…the two GARP objectives, dealing with weather and climate, are strongly related to each other. A better understanding of the physical processes that affect one means a better understanding of the processes that affect the other.”

This assumption, that progress on weather prediction can be expanded to climate prediction, could stand some examination, but it provides an important insight, which I’ve alluded to. For weather, which was wasplays out within the atmosphere, is a highly physical event. Mathematical reduction works well in that milieu and the global atmosphere was already well characterized. The idea to start with that and attach the rest of the climate system over time, made sense.

It get’s complicated, however, when you start adding living processes into the picture. For instance, the Physical Basis of Climate report states: “Research in general circulation modelling has so far been dominated by the problems of parameterizing (mathematizing) the purely atmospheric variables. The specification of the interaction between atmosphere and ground has only recently become an obvious limiting factor on realism.” An attached paper to the report, in it’s final remarks, puts the matter more starkly. “The account given may seem optimistic as to the possibilities of taking into account the various exchange processes between the atmosphere and the land surfaces. However, it is quite obvious that any noticeable success in this respect requires an extensive collaboration of geographers, soil scientists, hydrologists, botanists and geologists; in short the whole school of earth science is involved. It would be a remarkable achievement if such an objective could be accomplished.”

Has such an achievement been accomplished? It sees something more of the opposite happened. Though few know it, shortly before the IPPC was created, another organization called the International Geosphere Biosphere Program was created to look into many of these “exchange processes between the atmosphere and the land surfaces.” It was however, for reasons unclear, shuttered in 2015, losing the collaboration of many soil scientists, hydrologists and botanists, one must guess. The work, however, continued. There are now what are called Earth System Models (ESM) which, as put by Climateurope “seek to simulate all relevant aspects of the Earth system. They include physical, chemical and biological processes, therefore reaching far beyond their predecessors, the global climate models (GCM), which just represented the physical atmospheric and oceanic processes.”

As you see, the models evolve. It’s a procession of aggregation, adding in new variables as they are reduced to equations fit for modelling. What the original modelers referred to as a “machine,” today’s modelers would probably describe differently. What is key, though, and what is revealed along this evolution, is that the physical science basis is essentially a tool, not a theory. The physical science basis is a mathematical tool for the computer modelling of Earth’s climate system, originally applied to weather prediction and then vastly expanded to include the planet.

I think this is what the phrase, the physical science basis, was originally intended to point out. “Here’s what we can predict using this tool,” might well paraphrase its meaning. I think most scientists understand it that way. Millan was amused by my concerns about the physical science basis. “I see if you have a problem with the physical science basis,” he wrote me once. But he agreed with my observation that what the physical science basis essentially means is mathematical basis. “This is called reductionist science,” he wrote me. “Scientists normally break down a problem (process) into smaller parts, amenable to easy treatment. Smaller and smaller.” “Normally, once they solve that small problem, they are unable to put the puzzle back together again. Thus, the tendency to consider part solutions as the answer applicable to the whole.”

The point is, the physical science basis is a term intended for science, and it makes most sense within those boundaries where its meaning and limitations are understood. It’s when it crosses the border to society that things get weird, where you suddenly you wake up to discover everything from forests to farms to whales have been reduced to carbon quantities, and life itself is being financialized.

What happens when the physical science basis leaps the boundaries of science and enters society? That’s what we’ll consider in the next piece. We won’t go to space, like we did in the first episode, but we may get up into the sky. To properly see the “Climate Effects of Man-Made Surface Change,” one needs to look down from a cloud.

The Climate According to Life

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