Exporting Entropy

The trick that made fossil civilisation so economically intoxicating was that these entropy costs were externalised — paid for by future generations, downstream communities, and the global climate system — while the energy benefit was pocketed immediately.

Coal ash — formally coal combustion residuals (CCRs) — is the inorganic mineral fraction of coal that survives combustion. It comes in four main forms: fly ash (~60% of total), bottom ash (~20%), boiler slag (~5%), and flue-gas desulphurisation (FGD) gypsum (~15%). The yield ratio is roughly 10–15% of the coal mass burned in power generation — burning a tonne of coal leaves approximately 120 kg of ash.

Global coal consumption began the 20th century at roughly 900 million tonnes per year and climbed steadily, reaching ~2,500 Mt by 1970 and ~5,000 Mt by 2000. In 2024 it reached a record 9.1 billion tonnes, driven overwhelmingly by China, India, and Indonesia. Translating coal consumed into ash generated yields an estimated cumulative global production of somewhere between 50 and 70 billion tonnes of coal ash across the 20th century alone — a figure that dwarfs virtually every other anthropogenic solid waste stream in history.

The remaining ~10–15% is where the entropy cost becomes biologically acute. Coal ash routinely contains mercury, arsenic, lead, cadmium, chromium (particularly hexavalent Cr(VI)), selenium, beryllium, nickel, and vanadium. Arsenic and selenium have been found migrating off-site at nearly half of monitored US coal ash disposal sites, contaminating drinking water wells and waterways. Chronic exposure pathways are multiple: inhalation (respiratory and neurological damage), groundwater leaching (arsenic causes bladder and skin cancers; chromium VI causes stomach cancer), and bioaccumulation in fish populations — selenium accumulation has in some cases caused reproductive failure and local extinctions.

There is a radioactive dimension rarely acknowledged in public debate. Coal contains naturally occurring uranium, thorium, and their decay products — and these concentrate in the ash. Studies have found that coal ash is more radioactive than the low-level nuclear waste from many reactor operations.

Municipal solid waste is projected to accumulate 70.35 billion tonnes between 2016 and 2050. Coal ash — the residue of just one industrial process — comes in second at an estimated 45.55 billion tonnes over the same period. Plastic waste projects to around 8 billion tonnes. E-waste from electronic devices to roughly 2 billion tonnes. And all photovoltaic solar panel waste, across all panels expected to be retired worldwide by 2050, sits at a mid-estimate of barely 0.11 billion tonnes — 0.24% of the coal ash figure. As Hannah Ritchie summarised from the Mirletz et al. commentary: solar PV waste is "at least 99.6% less than coal ash and municipal waste."

The gaseous entropy export — carbon dioxide — is the one most consequential for planetary systems. Global coal combustion emitted approximately 15.4 Gt of CO₂ in 2023, representing around 40–41% of all fossil fuel emissions and over 25% of total anthropogenic greenhouse gas output. When you burn coal, you are converting a highly ordered, concentrated hydrocarbon lattice into dispersed carbon dioxide molecules spread across the global atmosphere: maximum entropy in the carbon cycle. The atmosphere has a finite capacity to re-export this entropy (as infrared radiation to space), and the rate at which we are loading it has begun to exceed that capacity, causing the system to warm. This is the thermodynamic root of climate change: we have overwhelmed the planet's entropy export pathway.

The qualitative entropy profile of renewable waste is also categorically different. Wind turbine blades are composed largely of fibreglass and carbon-fibre composite — inert, non-toxic, non-leaching materials classified as non-hazardous in the US and Europe. Solar panels are ~95% recyclable aluminium, glass, and silicon. Approximately 85–100% of wind turbine structural components (steel, copper, concrete) are recyclable at current technology.

The honest caveat: renewables have their own upstream entropy costs — silicon wafer manufacturing, steel tower smelting, rare earth element refining for some wind turbines, and lithium/cobalt/nickel mining for battery storage, often under weak regulatory regimes. These are real costs. But lifecycle analysis consistently shows the total entropy cost over an installation's operational life is 20 to 50 times lower in CO₂ terms than coal, and the solid waste comparison is orders of magnitude more favourable.