Published in The Linnean, Vol. 38, October 2022, pp14-20. It is also the write-up of a lecturethat I gave to the Linnean Society in February 2022.


82% of the total primary energy (BP 2022) used by humans on Earth is derived from the fossil fuels, whose combustion is causing global heating (from energy restrained from radiating into outer space by greenhouse gases) which impels climate change.

Although our overall use of energy has increased by about 13% during the past 10 years, the relative proportions of oil, gas, nuclear, and hydro in the energy-mix have changed very little. Coal use has fallen from 30% to 27%, but despite double-digit growth rates for renewables, total wind plus solar combined still account for less than 5% of global primary energy.

The lion’s share (31%) of our energy is furnished by crude oil, which is the lifeblood of industrial civilization; however, oil is becoming more difficult and consequently more expensive to produce. Before about 1930, for each barrel of oil’s worth of energy expended, in excess of 50 barrels of oil were recovered (Figure 1). Now, globally, this Energy Return on Investment (EROI) is less than 20, and for the heaviest oils, probably below 5, meaning that relentlessly larger amounts of energy must be consumed to maintain the flow of this critical resource (Rhodes 2014).

Lucas gusher well

Figure 1. The Lucas Gusher oil well, at Spindletop Hill, Texas in 1901. [This was the first gusher of the Texas oil boom]. Before about 1930, more than 50 barrels of oil could be recovered for one barrel of oil’s worth of energy expended. Now, the return is nearer 10 for US oil. [Credit: original photo by John Trost. w:en:Image:Lucas_gusher.jpg by Nv8200p, 4/12/2006 16:29 (UTC)]

 Oil Production and Use.

Annually, the human enterprise devours a massive 30 billion barrels of crude oil (BP 2022): 83 million barrels a day, or almost 1,000 barrels a second. Snap your fingers, and another 1,000 barrels of oil are gone. Until about 10 years ago, the world’s main oil producers were Saudi Arabia and Russia, but the United States has now joined this exclusive club as a result of its success in hydraulic fracturing (“fracking”), which allows large volumes of light tight oil to be recovered, mainly from low-permeable shale, and now accounts for almost two-thirds of US oil production (EIA 2022a).

Much of the oil remaining in the world is high-sulphur (sour) and heavy (e.g. from the Orinoco belt in Venezuela), needing more costly processing, and most of it is unrecoverable. “Extra-heavy” oil is not a freely flowing liquid but is bituminous, and resembles the black tar used for road surfacing. Sometimes, “statistics” are released, mainly to encourage investors, such as there is more oil (in the form of “oil shale”) under America than there is under Saudi Arabia (Rapier 2012), but this refers to an ancient solid material called kerogen, which needs to be heated to 400—500 deg C to turn it into a liquid that we recognise as oil; since this takes a lot of energy, the EROI is typically very low (Rhodes 2014).

Oil not only fuels transportation, but (including natural gas liquids) is the raw “carbon” chemical feedstock for plastics, chemicals, pharmaceuticals, and most modern devices, e.g. computers, cell phones etc. Without oil and natural gas (for fertilizers) modern agriculture could not exist, and it takes up to10 calories of fossil fuels to deliver each calorie of food onto the plate (Lott 2011). Some of the impacts of “industrialised” agriculture on the biosphere are illustrated in (Figure 2), which shows a field of soya being harvested in Brazil: the land itself was formerly rainforest, which has been cleared for crops, and the plumes of dust following the combine harvesters are topsoil, broken up by these heavy machines as they pass over it. Since the fields are left bare until the next crop is planted, erosion occurs, as the soil is blown or washed away. In a few years, the land loses its productivity, whereupon more rainforest is cleared: a relentless process of degradation. Even larger regions of the Brazilian Amazon are cleared to provide land on which to graze cattle for the meat industry (Butler 2021).

soya harvesting in Brazil

Figure 2. Field of soya being harvested in Brazil. Formerly this land was rainforest, and the plumes of dust following the combine harvesters are topsoil, broken up as they pass over it. Once the land becomes unproductive due to soil erosion, yet more forest is cleared. [Credit: Lou Gold (CC BY-NC-SA 2.0)]

Alternatives to Oil.

Although there will always be hydrocarbons in the ground, supplies of cheaply and easily procured oil are diminishing, and so we need to find alternative fuels, and carbon feedstocks for industry. Burning oil also contributes 12.4 billion tonnes (The World Counts 2022) of carbon dioxide to the atmosphere every year (a third of all CO2 emissions), which is driving catastrophic global climate change. Obviously, as oil-production wanes, we will emit far less carbon, but struggle to maintain the dynamics of a complex oil-dependent globalised civilization. Potential uncertainties in the geopolitical landscape, for example Russia’s invasion of Ukraine, also urge actions toward reducing national dependencies on imported oil and gas (Rhodes 2022).


Biofuels are often touted as a “low-carbon” solution to a declining oil supply, and yet in the UK, even if we converted all arable land over to making bioethanol, and grew no food, we could only match less than half (45%) of the liquid fuel demand currently met from petroleum. Similar yields of celluosic ethanol are expected from Miscanthus x giganteus (“Elephant Grass”), and although this can be grown on marginal land, large areas are still required. For biodiesel, made from rapeseed, the situation is even worse, and we could only produce one seventh (14%) of our liquid fuel requirements in this way (Rhodes 2015a), even allowing for the better “miles per gallon” obtained if all vehicles were fitted with diesel engines. Additionally, diesel fuel is needed to run tractors and combine harvesters to grow and harvest the biofuel crops, leading to a very low EROI, along with the consumption of large quantities of freshwater. Hence, it is unlikely that the currently less than 1% (BP 2022) of our total energy provided by biofuels will increase significantly.

What about fracking?

Hydraulic fracturing, popularly known as “fracking”, involves creating cracks in a shale layer by pumping a fluid into it under high pressure, so that the oil or gas trapped within can flow out (Figure 3). The procedure has sparked controversy, particularly in regard to potential environmental contamination and adverse health effects (Michaux 2019). Leakage of methane, not only from fracking operations (Vaughan 2020) but across the whole of the global oil and gas industry (IEA 2020), is a matter of great concern, given the very high global heating potential of the gas, as compared with carbon dioxide. Nonetheless, some 65% of US oil (EIA 2022a) and 79% of US natural gas are currently produced by fracking (EIA 2022b).

Fracking chart

Figure 3. Schematic depiction of hydraulic fracturing for shale gas, showing main possible environmental effects. [Credit Mikenorton]

In 2005, global output of conventional crude oil reached a plateau, and since then 71% of all growth in oil supply is from fracking, with much of the rest provided by extra-heavy oil (Michaux 2019). Outside of the US, the technology has proved far less successful, and given a persistently negative cash flow, the future viability of the shale industry is debatable. Should this falter, the global oil supply would struggle to meet demand, leading to soaring oil prices.

Decline in “cheap to produce” oil.

• 81% of global liquids production in decline by 5—7% = a loss of 3—4.5 mbd/year (Michaux 2019).

• Hence, just to maintain existing output, a new Saudi Arabia’s worth of production must be found every 3 years: 3 new Saudis by 2030!

• This new production will come mainly from “unconventional” oil (such as oil sands, light tight oil, coal and gas to liquids conversion) plus (ultra)deepwater drilling.

• Such unconventional oil is more difficult, energy intensive and expensive to produce.

• Highly uncertain how much light tight oil (from fracking shale) can be recovered; what the production rates might be; if it can take up slack from global existing field decline?

• Oil (= “all liquids”) demand back above 100 mbd, as global economies rebound post-Covid (Blas and Hurst 2021).

• From end-2014 to mid-2020, the market was oversupplied, forcing the oil price down (Figure 4): smaller investment at low oil prices, means less “new oil” coming online in the next few years:

• Supply “crunch” predicted: 2025-2030 (Michaux 2019).

Figure 4. Comparison of benchmark oil prices: low from end-2014 with price crash in April 2020 as a result of the Covid-19 pandemic. [Credit AKS.9955]

The Changing Climate and Overshoot.

The term “Changing Climate” has been used (Rhodes 2015b) to emphasise a set of world-scale problems, each often regarded in isolation, but which are actually mutually entangled threads of a complex system that is failing. Although “climate change” per se, is a major factor among them (driven by global heating from energy reined in by greenhouse gases), remedying this alone, e.g. through net-zero emissions strategies, will not resolve the overall problem, which is that the human species is in a condition of ecological overshoot:

[Overshoot = the hyperconsumption of natural resources, at rates much faster than they can be replenished, and in excess of the biosphere’s capacity to absorb and process the waste discharged through their use.]

However, to shrink the human enterprise so that it operates within the carrying capacity of the Earth demands very large reductions in our consumption. To arrive at an estimate of just how much, we can appeal to the Ecological Footprint Analysis (Global Footprint Network 2022), which suggests around 40% as a global average, but closer to 70% in the richer, industrialised nations (Figure 5). Such “one planet living” (Figure 6) requires a fundamental recasting of our goals and lifestyles, with far more substantive changes than essentially trying to preserve business as usual, merely with low-carbon energy in place of fossil fuels.

How many earth

Figure 5. Ecological footprints of nations. [Credit Footprint123]

Even if we chose to continue burning fossil fuels, depletion would substantially reduce their availability within the next few decades (Mohr et al. 2015). Hence, for this reason too, it is essential to find alternative energy sources. While it is debatable how much renewable energy might actually be installed (Seibert and Rees 2021), it is likely that matching the energy derived from all the coal, oil and gas currently burned will prove extremely difficult.

future pathways

Figure 6. Alternative pathways: overshoot to collapse (red lines); or, controlled contraction to “one planet living”, well within Earth’s human carrying capacity (green line). [Credit Prof. W.E.Rees].

Clearly, by reducing our energy demand, the amount of low-carbon energy that must be installed is brought down to more “manageable” levels. Significant energy savings are possible through relocalisation (so curbing unnecessary transportation and its fuel requirements), by properly insulating buildings and growing food locally. Such a strategy also helps to build resilience at the community level, and provides a buffer against global supply chain failures, e.g. resulting from freak weather events, vagaries such as Covid and Brexit, and geopolitical factors, including outbreaks of war.

Some symptoms of ecological overshoot.

• Increasing atmospheric CO2/global heating.

• Ocean acidification and ocean temperatures both rising.

• Melting ice sheets, glaciers, sea ice.

• Rising sea-levels.

• Loss of corals.

• Decimated fisheries.

• Deforestation and habitat loss.

• Draining of fossil aquifers, rivers and lakes.

• Erosion, nutrient depletion and loss of carbon from soils, desertification.

• Massive species displacement and extermination, insect die-off.

• Pollution of air, land, waterways, oceans – including by microplastics, and “forever chemicals”.

• Unsustainable consumption: 100 billion tonnes of (mostly non-renewable) “natural resources” each year – predicted to reach184 billion tonnes in 2050.

Even if we could switch our energy entirely to “net-zero” emissions, current consumption and waste discharge by the human “system” would continue to exceed and degrade the Earth’s biocapacity. This has been expressed succinctly (Seibert and Rees 2022) by the following analogy:

“What the passengers on the [MTI] Titanic need for survival is a dramatic course change, but what many of the ship’s engineers are proposing is to replace its FF engines with electric motors.”

Scientists’ Warnings.

The first Scientists Warning paper (Kendal 1992), stressed mainly the ecological damage then inflicted by humans, while a later study (Ripple et al 2017) demonstrated that the intervening twenty-five years had only witnessed further destruction of the ecosphere. The World Scientists’ Warning of a Climate Emergency report, published in 2019 (Ripple et al 2019) which has now been endorsed by a total of 14,594 scientists from 158 countries, emphasised a set of collective actions, aimed toward restoring and protecting natural ecosystems, conserving energy, reducing food waste, the adoption of a more plant-based diet, population control and economic reforms. However, two subsequent papers (Ripple et al, 2020a) and (Ripple at al. 2020b) merely confirmed a further, dramatic deterioration of all climate markers.

The “WORLD SCIENTISTS’ WARNINGS INTO ACTION” (SWIA) paper (Barnard et al. 2021) was published on Friday, November 12th (2021), formally the concluding day of the COP26 climate change conference, although a final agreement was not actually reached until late on the Saturday (13th). It is the “Into Action” qualifier that sets this publication apart from the previous warnings, since it offers practical means for steering away from the abyss, and toward a new territory where human needs are met, harmoniously, within the biocapacity of the Earth. SWIA summons all levels of leadership, from local to global, as are required to make real the proposed changes. Only immediate, rapid and far reaching action has a serious chance of keeping the Earth’s mean global temperature below the 1.5 degree limit.

Massive though this challenge is, it is really a single identifier of a whole system that is out of balance: a mechanism of resource hyperconsumption which transgresses several vital, but interwoven, planetary boundaries, powered by burning 15 billion tonnes of fossil fuels per year (Rhodes 2019). Since it is the system of civilization that must be fixed, any means to accomplish this must, of necessity, also be systemic in nature, and bring about a consolidated amelioration of climate change, biodiversity loss, and relentless degradation of the ecosphere.

The SWIA paper underlines six principal areas where effort must be focussed: Energy, Atmospheric Pollutants, Nature, Food Systems, Population Stabilisation, and Economic Reforms, of which the following is a highlighted summary:

  • Energy. Implement massive conservation practices: retrofitting buildings, relocalisation, buying less “stuff”, could halve UK energy demand. Transition from fossil fuels to low-carbon sources including solar and wind.
  • Atmospheric Pollutants. Rapidly cut emissions of methane, soot, HFCs and other short-lived climate pollutants. This could reduce the short-term warming trend by more than 50% over the next few decades.
  • Nature. Conserve, restore, rewild ecosystems such as forests, grasslands, peatlands, wetlands and mangroves, and allow a greater share of them to reach their ecological potential for sequestering atmospheric CO2.
  • Food. Shift to a more plant-based diet. Adopt more regenerative and local production methods: significantly reduce emissions of methane and other GHGs, reduce deforestation, build soil. Curb food waste: globally, at least one-third of all food produced is discarded. Place-based food systems.
  • Economic Reforms. Convert the economy from max GDP growth to one that operates within limits of the biosphere. Work towards regional self-reliance, and focus on restoring efficient levels of local production of food and consumer goods. Impose high taxes on high-carbon luxury goods/activities.
  • Population Stabilisation. Stabilize a global population that is increasing by 220,000 people a day, using approaches that ensure social and economic justice, such as guaranteeing education for young men and women and the availability of voluntary family planning services.

We urge all scientists to sign this paper, and act in a united effort to avoid a catastrophic collapse of civilisation.

The time is now or never. Cooperation is fundamental to our success, and only by uniting as a human family, on all levels from local to global, can we hope to achieve an equitable and concordant future on our Mother Planet.

“We are called to be architects of the future, not its victims.” – R. Buckminster Fuller (1895–1983).


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Seibert and Rees 2022. file:///C:/Users/Chris/Downloads/energies-15-00974%20(1).pdf

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Teaser photo credit: Plantação de Arroz perto de Rio do Sul-SC, Brasil. By Herr stahlhoefer – Own work, Public Domain,