Module 50: Ecosystems, Climate & Sustainability

The 10% rule describes average trophic transfer efficiency across ecosystems, not a hard physical limit. Some systems achieve 15–20% efficiency, particularly aquatic ones. Large carnivores evolved because the prey they hunt is often too large, too fast, or too dangerous for smaller predators — they occupy a niche defined by their ability to handle large prey, not by energy optimisation. They also often eat the entire prey including bones and organs, capturing more energy than the rule implies. The deeper answer: evolution selects for reproductive success, not energy efficiency. If being a lion is a viable reproductive strategy given available prey density, lions evolve. The 10% rule explains why apex predators are always rare, not why they don't exist.

The sun was also dimmer in the distant past — roughly 4% dimmer per billion years going back. Higher CO2 compensated for lower solar output to maintain temperatures compatible with liquid water. The relevant question is not the absolute CO2 level but the rate of change: life adapts to stable conditions over millions of years, but rapid changes outpace adaptation. Today's CO2 rise from 280 to 422 ppm has occurred in 170 years — geologically instantaneous. The Cambrian transition to high CO2 took millions of years. Ecosystems, ocean chemistry, and species can adapt to a new equilibrium; they cannot adapt to the speed of change now occurring. The Permian mass extinction (~252 Mya) was caused by rapid CO2 release from Siberian Traps volcanism — and it killed 90% of marine species. That's the relevant deep-time analogue, not background CO2 levels.

Many climate scientists and economists do advocate for nuclear — the IEA, IPCC, and most energy models include significant nuclear in low-emission scenarios. The resistance comes primarily from cost and construction time. A new nuclear plant in a Western country now costs $8–12 billion and takes 10–20 years to build. Solar and wind are cheaper, faster, and require no waste management. The IPCC AR6 includes nuclear in mitigation pathways but notes its high costs and long lead times compared to renewables. The practical case for nuclear is strongest for existing plants (extending their life is very cheap per tonne of CO2 avoided) and for hard-to-decarbonise sectors like industrial heat and shipping. The case against is primarily economic, not safety-based: nuclear deaths per TWh are actually among the lowest of any energy source.

The biodiversity crisis is real, severe, and arguably harder to reverse than climate change. Extinct species cannot be recovered; a stable climate, in principle, can be restored over centuries once emissions stop. Current extinction rates are genuinely 100–1,000 times the background rate based on fossil evidence, though some researchers argue these estimates carry high uncertainty. The Living Planet Index (WWF) found a 69% average decline in monitored vertebrate populations since 1970 — not extinctions, but catastrophic abundance losses. The most important distinction from public debate: most attention goes to charismatic megafauna (tigers, rhinos), but the actual crisis is in insects, freshwater species, and soil organisms — less visible but ecologically foundational. A world with fewer tigers is aesthetically poorer; a world with 40% fewer insects, as documented in European entomological surveys, risks collapse of pollination and food chains.

The vast majority of existing carbon offsets do not deliver the claimed emissions reductions. A 2023 investigation by The Guardian, Zeit, and SourceMaterial found that over 90% of Verra's rainforest offset credits — the world's leading offset standard — were "phantom credits" with no real impact on deforestation. The core problems are additionality (would the forest have been saved anyway?), permanence (forests burn down), and measurement (baseline emissions are estimated, not measured). Well-designed offsets can work — the EU ETS allowances and some industrial process offsets have verified reductions. But voluntary market offsets used for "carbon neutral" product claims are almost universally unreliable. The honest use of offsets is as a temporary bridge while reducing emissions, not as a substitute for them. Using offsets to claim "net zero" while maintaining emissions is greenwashing by definition.

Cheapest new capacity is not the same as the cheapest to replace existing capacity. Fossil fuel infrastructure — power plants, pipelines, refineries — has been written down over decades and has near-zero marginal cost. Replacing working assets with new ones incurs capital costs even if the new source is cheaper on a levelised cost basis. Grid infrastructure, transmission lines, and storage all require massive investment. Permitting timelines for new renewables are astonishingly slow: in the UK, an offshore wind project averages 4–5 years of permitting before construction begins. Political opposition from fossil fuel industries has suppressed carbon pricing, which would accelerate transition. And roughly 70% of the energy system is not electricity — shipping, aviation, steel, cement, and heat are far harder to electrify and have seen almost no transition yet. The rate is accelerating but is not fast enough: the IEA's Net Zero by 2050 scenario requires tripling renewable capacity by 2030.

Peatlands alone store roughly 550–650 GtC — about as much as the entire atmosphere. They cover only 3% of Earth's land surface but have been accumulating carbon for thousands of years under waterlogged, anaerobic conditions that prevent decomposition. When peatlands are drained for agriculture (palm oil, soy, cattle) or fuel extraction (e.g., Scottish and Irish peat burning), this carbon is released as CO2 and methane over years to decades. Indonesia's drained peatlands emit roughly 0.5–1 GtCO2e/year — comparable to Germany's total annual emissions. The UK's upland peat bogs, many degraded by overgrazing and drainage, now emit more carbon than they absorb. Restoration (rewetting) is possible and cost-effective: re-wetting one hectare of drained peat can sequester 2–5 tCO2e/year at a cost of £50–200/tonne — competitive with most mitigation options.

The strongest serious argument — not denial, but a genuine policy debate — is about optimal timing and distribution of costs. William Nordhaus (Nobel laureate) argued that gradual carbon pricing rising over decades is economically optimal because discounting future damages justifies lower near-term action, and because future generations will be wealthier and better equipped to adapt. A more defensible current critique is that rapid decarbonisation of the global energy system may require imposing large costs on developing nations that contributed negligibly to the problem — a climate justice concern. Some economists argue that adaptation investment delivers more near-term welfare per dollar than mitigation in the poorest countries. The counterarguments are compelling (discount rates are ethically contestable, tipping points make gradual approaches catastrophically risky, renewable costs now make deep decarbonisation cheap), but the distributional justice question about who bears transition costs is genuine and unresolved.