Energy, the economy and the future: Key terms, quiz and sources

Understanding Energy / Module 14: Energy, the economy and the future Wrap-up

Energy, the economy and the future: review

Key terms

Energy intensity: Primary energy used per unit of GDP; lower values mean more output per unit of energy.
Purchasing-power parity (PPP): A way of converting GDP between currencies that reflects what money actually buys locally.
Human Development Index (HDI): A UN composite of life expectancy, education and income, ranging from 0 to 1.
Infant mortality rate: Deaths of children under one year old per 1,000 live births; Smil's preferred single measure of quality of life.
Energy poverty: Lack of access to electricity and clean cooking, or energy use too low to meet basic needs.
Traditional biomass: Wood, crop residues, dung and charcoal burned in simple stoves or open fires, often left out of commercial energy statistics.
External cost: A cost of producing or using energy, such as air pollution damage, that is borne by others and not included in the market price.
Energy subsidy: Government support that lowers the price paid by consumers or raises the price received by producers.
Learning rate: The percentage fall in a technology's cost each time its cumulative production doubles.
Integration costs: The extra costs of storage, grids and backup needed to supply reliable power from variable sources.
Energy security: The uninterrupted availability of energy at an affordable price.
Emergency oil stocks: Oil held by IEA members equal to at least 90 days of net imports, for release in a supply crisis.
Liquefied natural gas (LNG): Natural gas cooled to about -162 C so it can be shipped by tanker and regasified at the destination.
Fatal discontinuity: Smil's term for a rare, sudden event, such as a pandemic, mega-eruption or major war, that can change the course of history.
Risk per person-hour: Deaths per person per hour of exposure, a common scale for comparing very different risks.
Exponential growth: Growth by a constant percentage each period, so that the amount added keeps increasing.
Rule of 70: Doubling time is roughly 70 divided by the annual growth rate in per cent.
Logistic curve: An S-shaped growth path that starts slowly, accelerates, then levels off near a ceiling.
Scenario: A consistent, conditional description of a possible future, used to explore choices rather than to predict.
Chokepoint: A narrow sea passage, such as the Strait of Hormuz, through which a large share of world energy trade must pass.

Try it in the table

Open the Energy-intensive industry tile and note which industries it lists. Use the table in Part 1 to explain why a country with a large share of these industries will show high energy intensity even if its plants are efficient.
Open Heat pumps, air conditioning and refrigeration and look for the efficiency range it gives for air conditioners. Estimate how much electricity India could save if its fourfold growth in air conditioners used the best units rather than the worst.
Open Boilers, furnaces and stoves and Firewood and charcoal supply. Compare the efficiency of a traditional biomass stove with an LPG burner, and relate it to the household energy ladder in Part 2.
Open the LNG chain tile and Fuel stocks and strategic reserves. Check the liquefaction losses against the flow diagram in Part 3, and note how long emergency stocks would last a large importer in a full cut-off.
Open Solar photovoltaics and Lithium iron phosphate batteries. Look for what each says about cost declines, and apply the learning-curve idea from Part 1 to judge whether those declines are likely to continue.
Open Nuclear fission reactors and the Thermal coal commodity tile, and set what they say about safety and pollution against the deaths per TWh table in Part 3.

Final quiz

Smil found a worldwide correlation between energy use and GDP per person above 90%. What did he find among rich countries with similar incomes?

Japan and the large European economies use about half as much per person as the US at comparable living standards, because climate, structure and habits differ.

How can world energy intensity fall for decades while world energy use keeps rising?

Energy use equals GDP times intensity. If GDP grows 3% and intensity falls 1.5%, energy use still grows about 1.5%.

About what energy use per person is linked with an HDI above 0.8 in Smil's analysis?

At about 60 to 65 GJ a year societies can reach an HDI above 0.8; the best outcomes appear around 110 GJ.

Roughly how many people does the IEA count as still lacking electricity?

About 730 million, mostly in sub-Saharan Africa, with nearly 2 billion relying on polluting cooking fuels.

The Tsar Bomba test of 1961 released about 210 PJ. How does that compare with the Hiroshima bomb's 63 TJ?

210 PJ is 210,000 TJ, and 210,000 divided by 63 is about 3,300.

What did Europe's 2022 gas crisis reveal about LNG?

Cargoes go to the highest bidder, so a rich buyer's scramble raises prices for everyone, including South Asian importers.

Solar generation grew 30% in 2025. Using the rule of 70, what is its approximate doubling time at that rate?

70 divided by 30 is about 2.3 years. Growth this fast cannot continue for long, so solar's S-curve must bend.

Which electricity source has the lowest deaths per TWh in the Our World in Data estimates?

Solar is about 0.02 deaths per TWh, with nuclear and wind close behind; gas is about 2.8, hydro 1.3 and biomass 4.6.

Sources for this module

Smil, Energy at the Crossroads: Global Perspectives and Uncertainties (2003) · via Smil Mastery Course, M13 'Energy and economic growth', 'Energy intensity', 'Energy and the quality of life', 'Prices, real costs and energy in war'; M16 'Against forecasting'
Smil, Global Ecology: Environmental Change and Social Flexibility (1993) · via Smil Mastery Course, M13 'Energy and economic growth', 'Energy intensity'
Smil, Energy in Nature and Society: General Energetics of Complex Systems (2008) · via Smil Mastery Course, M13 'Energy and economic growth', 'Prices, real costs and energy in war'
Smil, Grand Transitions: How the Modern World Was Made (2021) · via Smil Mastery Course, M13 'Energy and economic growth'
Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M13 'Energy and economic growth', 'Energy in the developing world', 'Prices, real costs and energy in war'
Smil, China's Past, China's Future: Energy, Food, Environment (2004) · via Smil Mastery Course, M13 'Energy intensity'
Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M13 'Energy and the quality of life', 'Prices, real costs and energy in war'; M16 'Understanding risks quantitatively'
Smil, How the World Really Works: A Scientist's Guide to Our Past, Present and Future (2022) · via Smil Mastery Course, M13 'Energy and the quality of life'; M16 'Understanding risks quantitatively'
Smil, Energy in the Developing World: The Real Energy Crisis (ed. with W. Knowland, 1980) · via Smil Mastery Course, M13 'Energy in the developing world'
Smil, Energy in China's Modernization: Advances and Limitations (1988) · via Smil Mastery Course, M13 'Energy in the developing world'
Smil, Global Catastrophes and Trends: The Next Fifty Years (2008) · via Smil Mastery Course, M13 'Prices, real costs and energy in war'; M16 'Against forecasting', 'Fatal discontinuities'
Smil, Energy Myths and Realities: Bringing Science to the Energy Policy Debate (2010) · via Smil Mastery Course, M16 'Against forecasting'
Smil, Growth: From Microorganisms to Megacities (2019) · via Smil Mastery Course, M15 'Growth trajectories: linear, exponential, logistic'
Energy Institute, Statistical Review of World Energy 2025 (2025) web ↗ · 2024 world primary energy of 592 EJ and country totals, https://www.energyinst.org/statistical-review; per-person values are rounded calculations using UN population estimates
IEA, India Energy Outlook 2021 (2021) · key findings as summarised by Drishti IAS, 18 February 2021, https://www.drishtiias.com/daily-updates/daily-news-analysis/india-energy-outlook-2021-iea/print_manually
IEA, World Energy Outlook 2024 (2024), India findings as reported by PTI · Outlook Business, 17 October 2024, https://www.outlookbusiness.com/sustainability/india-set-to-lead-global-energy-demand-growth-coal-will-remain-central-iea
IEA, World Energy Outlook 2025 (2025) · Overview and key findings, https://www.iea.org/reports/world-energy-outlook-2025/overview-and-key-findings
Carbon Brief, 'IEA: Fossil-fuel use will peak before 2030 unless stated policies are abandoned' (November 2025) · summary of IEA World Energy Outlook 2025 scenario results, https://www.carbonbrief.org/iea-fossil-fuel-use-will-peak-before-2030-unless-stated-policies-are-abandoned/
ACCR, Investor bulletin: IEA World Energy Outlook 2025 (13 November 2025) · comparison of WEO 2025 scenarios with the 2015 and 2019 editions, storage capacity by scenario, https://www.accr.org.au/downloads/13112025-investor-bulletin-weo-2025.pdf
Ember, Global Electricity Review 2026 (April 2026) · 2025 data, https://ember-energy.org/latest-insights/global-electricity-review-2026/ and https://ember-energy.org/chapter/2025-in-review/
IEA, A 10-Point Plan to Reduce the European Union's Reliance on Russian Natural Gas (2022) · Russian share of EU gas imports and use in 2021, https://www.iea.org/reports/a-10-point-plan-to-reduce-the-european-unions-reliance-on-russian-natural-gas
IEA, Energy Efficiency 2025 (2025) · global energy intensity improvement and the COP28 goal of doubling it, https://www.iea.org/reports/energy-efficiency-2025
Ritchie, H., 'What are the safest and cleanest sources of energy?', Our World in Data (2020, updated 2022) · deaths per TWh from accidents and air pollution, based on Markandya and Wilkinson (2007) and Sovacool et al. (2016), https://ourworldindata.org/safest-sources-of-energy
Planète Énergies, 'World energy consumption in 2024' (2025) · per-person primary energy by region from the Energy Institute Statistical Review 2025, https://www.planete-energies.com/en/media/figures/world-energy-consumption-2019
Press Information Bureau, Government of India, 'Pradhan Mantri Ujjwala Yojana' factsheet (2021) · launch on 1 May 2016 and 8.48 crore connections by 20 October 2021, https://www.pib.gov.in/FactsheetDetails.aspx?Id=148555
Ministry of Petroleum and Natural Gas, Government of India, 'Strategic crude oil storage' · 5.33 MMT at Visakhapatnam (1.33), Mangaluru (1.5) and Padur (2.5), https://mopng.gov.in/en/pdc/investible-projects/oil-amp-gas-infrastructure/strategic-crude-oil-storage
IEA, 'IEA members endorse largest-ever oil stock release amid Middle East market disruptions' (11 March 2026) · statement as published at https://ieu-monitoring.com/editorial/iea-members-endorse-largest-ever-oil-stock-release-amid-middle-east-market-disruptions/894579/; member volumes via Enerdata, https://www.enerdata.net/publications/daily-energy-news/iea-member-countries-agree-release-400-mbl-oil-stocks.html
IEA, Oil Market Report, April 2026 (2026) · supply, Hormuz loadings, bypass exports, prices and demand, https://www.iea.org/reports/oil-market-report-april-2026
IEA, Oil Market Report, July 2026 (2026), as reported by Oil & Gas Journal · 'IEA: Oil market recovery clouded as Hormuz ceasefire collapses', 10 July 2026, https://www.ogj.com/general-interest/economics-markets/news/55390096/iea-oil-market-recovery-clouded-as-hormuz-ceasefire-collapses