What are the safest and cleanest sources of energy?

Energy has been critical to the human progress we’ve seen over the last few centuries. As the United Nations rightly says: “energy is central to nearly every major challenge and opportunity the world faces today.”

But while energy brings us massive benefits, it’s not without its downsides. Energy production can have negative impacts on human health and the environment in three ways.

The first is air pollution: millions of people die prematurely every year as a result of air pollution. Fossil fuels and the burning of biomass – wood, dung, and charcoal – are responsible for most of those deaths.

The second is accidents. This includes accidents in the mining and extracting of fuels – coal, uranium, rare metals, oil, and gas. It also includes accidents in transporting raw materials and infrastructure, the construction of the power plant, or their maintenance.

The third is greenhouse gas emissions: fossil fuels are the main source of greenhouse gases, the primary driver of climate change. In 2020, 91% of global CO₂ emissions came from fossil fuels and industry.¹

No energy source is completely safe. They all have short-term impacts on human health, either through air pollution or accidents. And they all have long-term impacts by contributing to climate change.

But, their contribution to each differs enormously. Fossil fuels are both the dirtiest and most dangerous in the short term and emit the most greenhouse gases per unit of energy. This means that there are thankfully no trade-offs here: low-carbon energy sources are also the safest. From the perspective of both human health and climate change, it matters less whether we transition to nuclear power or renewable energy and more that we stop relying on fossil fuels.

Nuclear and renewables are far, far safer than fossil fuels

Before we consider the long-term impacts of climate change, let’s look at how each source stacks up in terms of short-term health risks.

To make these comparisons fair, we can’t just look at the total deaths from each source: fossil fuels still dominate our global electricity mix, so we would expect that they would kill more people.

Instead, we compare them based on the estimated number of deaths they cause per unit of electricity. This is measured in terawatt-hours. One terawatt-hour is about the same as the annual electricity consumption of 150,000 citizens in the European Union.²

This includes deaths from air pollution and accidents in the supply chain.³

Let’s look at this comparison in the chart. Fossil fuels and biomass kill many more people than nuclear and modern renewables per unit of electricity. Coal is, by far, the dirtiest.

Even then, these estimates for fossil fuels are likely to be very conservative. They are based on power plants in Europe, which have good pollution controls and are based on older models of the health impacts of air pollution. As I discuss in more detail at the end of this article, global death rates from fossil fuels based on the most recent research on air pollution are likely to be even higher.

Our perceptions of the safety of nuclear energy are strongly influenced by two accidents: Chernobyl in Ukraine in 1986 and Fukushima in Japan in 2011. These were tragic events. However, compared to the millions that die from fossil fuels every year, the final death tolls were very low. To calculate the death rates used here, I assume a death toll of 433 from Chernobyl, and 2,314 from Fukushima.⁴ If you are interested, I look at how many died in each accident in detail in a related article.

The other source which is heavily influenced by a few large-scale accidents is hydropower. Its death rate since 1965 is 1.3 deaths per TWh. This rate is almost completely dominated by one event: the Banqiao Dam Failure in China in 1975. It killed approximately 171,000 people. Otherwise, hydropower was very safe, with a death rate of just 0.04 deaths per TWh – comparable to nuclear, solar, and wind.

Finally, we have solar and wind. The death rates from both of these sources are low but not zero. A small number of people die in accidents in supply chains – ranging from helicopter collisions with turbines, fires during the installation of turbines or panels, and drownings on offshore wind sites.

People often focus on the marginal differences at the bottom of the chart – between nuclear, solar, and wind. This comparison is misguided: the uncertainties around these values mean they are likely to overlap.

The key insight is that they are all much, much safer than fossil fuels.

Nuclear energy, for example, results in 99.9% fewer deaths than brown coal; 99.8% fewer than coal; 99.7% fewer than oil; and 97.6% fewer than gas. Wind and solar are just as safe.

Putting death rates from energy in perspective

Looking at deaths per terawatt-hour can seem abstract. Let’s try to put it in perspective.

Let’s consider how many deaths each source would cause for an average town of 150,000 people in the European Union, which – as I’ve said before – consumes one terawatt-hour of electricity per year. Let’s call this town ‘Euroville’.

If Euroville were completely powered by coal, we’d expect at least 25 people to die prematurely every year from it.  Most of these people would die from air pollution.

This is how a coal-powered Euroville would compare with towns powered entirely by each energy source:

• Coal: 25 people would die prematurely every year;
• Oil: 18 people would die prematurely every year;
• Gas: 3 people would die prematurely every year;
• Hydropower: In an average year, 1 person would die;
• Wind: In an average year, nobody would die. A death rate of 0.04 deaths per terawatt-hour means every 25 years, a single person would die;
• Nuclear: In an average year, nobody would die – only every 33 years would someone die.
• Solar: In an average year, nobody would die – only every 50 years would someone die.

The safest energy sources are also the cleanest

The good news is that there is no trade-off between the safest sources of energy in the short term and the least damaging for the climate in the long term. They are one and the same, as the chart below shows.

In the chart on the left-hand side, we have the same comparison of death rates from accidents and air pollution that we just looked at. On the right, we have the amount of greenhouse gases emitted per unit of electricity production.

These are not just the emissions from the burning of fuels but also the mining, transportation, and maintenance over a power plant’s lifetime.⁵

Coal, again, is the dirtiest fuel. It emits much more greenhouse gases than other sources – more than a hundred times more than nuclear.

Oil and gas are also much worse than nuclear and renewables but to a lesser extent than coal.

Unfortunately, the global electricity mix is still dominated by fossil fuels: coal, oil, and gas account for around 60%. If we want to stop climate change, we have a great opportunity in front of us: we can transition away from them to nuclear and renewables and also reduce deaths from accidents and air pollution as a side effect.⁶

This transition will not only protect future generations, but it will also come with huge health benefits for the current one.

Methodology and notes

Global average death rates from fossil fuels are likely to be even higher than reported in the chart above

The death rates from coal, oil, and gas used in these comparisons are sourced from the paper of Anil Markandya and Paul Wilkinson (2007) in the medical journal, The Lancet. To date, these are the best peer-reviewed references I could find on the death rates from these sources. These rates are based on electricity production in Europe.

However, there are three key reasons why I think that these death rates are likely to be very conservative, and the global average death rates could be substantially higher.

• European fossil fuel plants have strict pollution controls. Power plants in Europe tend to produce less pollution than the global average and much less than plants in many low-to-middle-income countries. This means that the pollution generated per unit of electricity will likely be higher in other parts of the world.
• In other countries, more people will live closer to power plants and be exposed to more pollution. If two countries produce the same amount of coal power and both have the same pollution controls, the country where power plants are closer to urban centers and cities will have a higher death toll per TWh. This is because more people will be exposed to higher levels of pollution.Power plants in countries such as China tend to be located closer to cities in many countries than they are in Europe, so we would expect the death rate to be higher than the European figures found by Markandya and Wilkinson (2007).⁷
• More recent research on air pollution suggests the health impacts are more severe than earlier research suggested. The analysis by Markandya and Wilkinson was published in 2007. Since then, our understanding of the health impacts of air pollution has increased significantly. More recent research suggests the health impacts are more severe. My colleague, Max Roser, shows this evolution of the research on air pollution deaths in his review of the literature here.Another reason to suspect that the global average rates are much higher is the following: if we take the death rates from Markandya and Wilkinson (2007) and multiply them by global electricity production, the resulting estimates of total global deaths from fossil fuel electricity are much lower than the most recent research.If I multiply the Markandya and Wilkinson (2007) death rates for coal, oil, and gas by their respective global electricity outputs in 2021, I get a total death toll of 280,000 people.⁸This is much lower than the estimates from more recent research. For example, Leliveld et al. (2018) estimate that 3.6 million die from fossil fuels yearly.⁹ Vohra et al. (2021) estimate more than double this figure: 8.7 million.¹⁰Not all deaths from fossil fuel air pollution are due to electricity production. But we can estimate how many deaths do. In a recent paper, Leliveld and his colleagues estimated the breakdown of air pollution deaths by sector. They estimate that 12% of all (fossil fuel and pollution from other sources) air pollution deaths come from electricity production.¹¹

By my calculations, we would expect that 1.1 million to 2.55 million people die from fossil fuels used for electricity production each year.¹²The estimates we get from Markandya and Wilkinson (2007) death rates undercount by a factor of 4 to 9. This would suggest that actual death rates from fossil fuels could be 4 to 9 times higher. That would give a global average death rate from coal of 93 to 224 deaths per TWh.Unfortunately, we do not have more up-to-date death rates for coal, oil, and gas to reference here, but improved estimates are sorely needed. The current death rates shown are likely to be underestimated.

We need a timely global database on accidents in energy supply chains

The figures we reference on accidents from nuclear, solar, and wind are based on the most comprehensive figures we have to date. However, they are imperfect, and no timely dataset tracking these accidents exists. This is a key gap in our understanding of the safety of energy sources – and how their safety changes over time.

To estimate death rates from renewable energy technologies, Sovacool et al. (2016) compiled a database of energy-related accidents across academic databases and news reports. They define an accident as “an unintentional incident or event at an energy facility that led to either one death (or more) or at least $50,000 in property damage,” which is consistent with definitions in the research literature.

This raises several questions about which incidents should and shouldn’t be attributed to a given energy technology. For example, included in this database were deaths related to an incident where water from a water tank ruptured during a construction test at a solar factory. It’s not clear whether these supply chain deaths should or shouldn’t be attributed to solar technologies.

The comparability of these incidents across the different energy technologies is, therefore, difficult to assess with high certainty. One additional issue with this analysis by Sovacool et al. (2016) is that its database search was limited to English reports or non-English reports that had been translated. Some of these comparisons could therefore be a slight over- or underestimate. It is, however, unlikely that the position of these technologies would change significantly – renewable and nuclear technologies would consistently come out with a much lower death rate than fossil fuels. Consistent data collection and tracking of incidents across all energy technologies would greatly improve these comparisons.

We need improved estimates of the health impacts of the mining of minerals and materials for all energy sources

The figures presented in this research that I rely on do not include any health impacts from radiation exposure from the mining of metals and minerals used in supply chains.

While we might think that this would only have an impact on nuclear energy, analyses suggest that the carcinogenic toxicity of other sources – including solar, wind, hydropower, coal and gas are all significantly higher across their supply chains.¹³

These figures only measure potential exposure to toxic elements for workers. They do not give us estimates of potential death rates, which is why we do not include them in our referenced figures above.

However, the inclusion of these figures would not change the relative results, overall. Fossil fuels – coal, in particular – have a higher carcinogenic toxicity than both nuclear and renewables. Hence the relative difference between them would actually increase, rather than decrease. The key insight would still be the same: fossil fuels are much worse for human health, and both nuclear and modern renewables are similarly safe alternatives.

However, estimates of the health burden of rare minerals in energy supply chains is still an important gap to fill, so that we can learn about their impact and ultimately reduce these risks moving forward.

Hannah Ritchie (2020) - “What are the safest and cleanest sources of energy?” Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/safest-sources-of-energy' [Online Resource]

@article{owid-safest-sources-of-energy,
    author = {Hannah Ritchie},
    title = {What are the safest and cleanest sources of energy?},
    journal = {Our World in Data},
    year = {2020},
    note = {https://ourworldindata.org/safest-sources-of-energy}
}

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