The "second" warming problem -- finally on Twitter!

The deep problems we face from our ever-growing energy use seem to be gaining attention. A Harvard astronomer was the first to mention the idea in 2008, as I recently learned.

There’s an interesting story behind the above headline, recognizing the problem of planetary heating from human waste heat, way back in 2009. Hardly anyone mentions it today. But that may be changing a little. More on the headline below.

Over the holiday period I came across a tweet by Stefan Rahmstorf, a well-known climate scientist from the University of Potsdam. Rahmstorf is an expert in oceanic flows, and in predicting future climate impacts. Most of his work is in the center of modern climate science, looking at the trends with global warming and what it might do to our climate in the near future. But this tweet was different:

Stefan Rahmstorf 🌏 fediscience.org/@rahmstorf 🦣 @rahmstorf

Nuclear #fusion will not only come too late to help solve the #climatecrisis. Even in the long run it will not be the unlimited energy source that some are dreaming of. The reason is basic physics, and anyone can do the back-of-envelope calculation. 🧵1/

What continues, if you read through the thread, is a basic outline of the argument I and others have been making that we will ultimately face an even bigger problem than greenhouse gas warming due to the waste heat we generate. It’s great to see this gaining more attention.

Among other things, Rahmstorf also mentioned that a PhD student of his, Peter Steiglechner, wrote his masters’ thesis on the problem in 2018, which I will read as soon as possible.

But I can certainly understand why Rahmstorf and other climate scientists don’t discuss this issue more prominently, as it is — without doubt — not as urgent as our problem with greenhouse gases. Not yet. But it is, at the same time, more fundamental. It doesn’t reflect a problem with one source of energy, but with any source of energy, nuclear fusion among them.

In brief, no matter where we get our energy from, once we use that energy — by heating homes, making cement, transporting people or things — the spent energy ultimately ends up in the environment as heat. It may take a longer or shorter time to get there, but it will get there. Right now, as Rahmstorf points out, the waste heat we produce is heating the planet, but is only about 1/30th of the imbalance due to greenhouse gases. The greenhouse gas problem is more serious.

But the history of energy use shows that we double the rate at which we use energy every 35 years or so, which means that in about five doubling times — 175 years or so — the waste heat problem will be just as big as the greenhouse gas problem is now. If we make a big leap in energy use due to something like “cheap and unlimited” nuclear fusion, we might just get there a lot sooner.

This great paper by a pair of engineers from 2008 ago explains the issue very clearly.

Last week I also learned something fascinating about the origins of this understanding of the problem of waste heat. In all honesty, I thought those two engineers — Nick Cowern and Chihak Ahn — were the first to identify this issue, and I’ve been writing about it on and off ever since. As far as I can tell, these two were among the first to write about this issue, but two weeks ago I stumbled across a parallel and independent early discussion of similar ideas in a 2008 paper published by Harvard astrophysicist Eric Chaisson in 2008. This paper gives an elegant discussion of the problem. Here’s the abstract:

Even if civilization on Earth stops polluting the biosphere with greenhouse gases, humanity could eventually be awash in too much heat, namely, the dissipated heat by-product generated by any nonrenewable energy source. Apart from the Sun's natural aging—which causes an approximately 1% luminosity rise for each 10^8 years and thus about 1°C increase in Earths surface temperature—well within 1000 years our technological society could find itself up against a fundamental limit to growth: an unavoidable global heating of roughly 3°C dictated solely by the second law of thermodynamics, a bio-geophysical effect often ignored when estimating future planetary warming scenarios.

Having learned of this, I couldn’t help but try to track down Prof. Chaisson. I found his email and sent him a message, and received a wonderful reply, part of which discussed the history of that 2008 paper. Here’s this part of the email:

It was on a night flight, Paris-Boston ~2006, after a UNESCO meeting on the environment (I being the only physicist among climate experts, ecologists, diplomats, etc.) when it dawned on me that they (meaning the IPCC) were overlooking something.  While others on the plane slept, I crunched some numbers literally on the back of an envelope . . . and then hoped I was wrong, that is, hoped that I was incorrect in thinking that the very act of using energy heats the air, however slightly now. 

So I wrote it up and sent it in, yet it took well more than a year for my 1-page contribution to get into print.  Two referees at AGU/Eos loved it, but a third tried his damnedest to kill it—“irrelevant and distracting” he said, repeatedly.  Anyway, it got some traction when the paper appeared, such as on the front page of the Boston Globe and a run on the big supercomputer at NCAR where Flanner, out to prove it wrong I think, found, after his machine crunched for many hours, the same result I had on the envelope. 

The cover of the Boston Globe article from 2009 is what I’ve used at the head of this article. Amazing how big and important ideas can get noticed… and then almost immediately forgotten.

Chaisson went on to mention another issue which I am aware of, but have certainly paid much less attention to, which is the local heating due to the concentration of human energy use in cities. Almost all human activities are concentrated in cities, and energy use is as well. Apparently, heating effects from such energy can already be detected:

[Flanner of NCAR] went on to show how, although anthropogenic heat flux from waste heat now is hardly 0.1C globally, it sure is mounting where people cluster, such as cities where now 55% of everyone lives and by 2050 likely some 70% of all people using upwards of 85% of all energy used.  Anthropogenic heat flux is surely a factor around population centers, contributing to heat-island effects and Flanner’s maps show how that waste heat will grow over the course of this century.  Regional waste-heat warming of parts of continents are approaching 0.5C and might reach as high as 1C by the year 2100.

One of the most important sub-texts of the early papers on warming from waste heat is that every source of energy will contribute to the problem. Going from fossil fuels to fusion energy does nothing to alleviate the issue. However, as examined closely in the 2008 paper by Cowern and Ahn, some sources of energy are less problematic than others because those energy sources are ALREADY heating the Earth. Drawing on these sources means we may add no net energy to the Earth energy budget, and not bring on the waste heat problem. What sources are these? Of course, anything linked to solar energy.

This is a topic I should revisit. But I’ll just finish here with the ending of Prof. Chaisson’s email where he offers his view on this issue:

I’m now of the opinion, in a nutshell, that any energy that’s dug up on Earth—including all fossil fuels of course, but also nuclear and ground-sourced geothermal—will inevitably produce waste heat as a byproduct of humankind’s use of energy.  The only exception to that is energy arriving from beyond Earth, this is energy here and now and not dug up, namely the many solar energies (plural) caused by the Sun’s rays landing here daily. 

That is, shining light, blowing wind, falling water, and warming air are all caused by and derived from Ole Sol and, when captured and used, they will not add waste heat to our surface environment—because they will dump the energy right back into the air after use.  Each one of these acquires energy that’s present daily, gets used by society (both that gainfully used usefully by us and also that inefficiently used and useless), and then gets dissipated back into the environment at some temperature T—all of it, no net energy (or heat) is gained or lost.  The need to avoid waste heat is indeed the single, strongest, scientific argument to embrace solar energies of all types.

Just to end, I should also like to mention a new paper which Eric has just published. This is titled “Energy Budgets of Evolving Nations and Their Growing Cities.” Energies, 2022, v15, article 8212. https://doi.org/10.3390/en15218212

The paper is also available online here.

I haven’t read this yet, but will be doing so shortly. Eric describes it as an analysis of the energy evolution of “nations and cities and how they will likely succeed or fail depending on how they manage their energy budgets.”

As always, getting a clear look at the role of energy is crucial to understanding almost anything.