Is CO₂ Still the Most Maligned Gas in History? — Eight Years On

In the middle of August homes were destroyed as wildfires brought devastation to parts of Britain. The apocalyptic vision of the world on fire, with wildfires raging across Europe and the UK, prompted me to look again at a post I wrote eight years ago, Is CO₂ the Most Maligned Gas in History?. I wrote it in December 2018 when I was sceptical of the evidence attributing most recent climate change to human activity. Eight years later, I think some of the questions I raised remain worth asking, but the scientific answers have become considerably clearer.

The post is still relevant as a historical account of the debate, and some of its points remain valid. CO₂ is essential to life, it is quite different from conventional air pollutants, and mining will be essential to any large-scale transition away from fossil fuels. But its central scientific position, that climate change was probably mainly natural and that the contribution from human activity was uncertain, is no longer supported by the evidence.

In the 2018 article I wrote: “An increase in 40% [of CO₂] seems a lot, but in absolute terms this is an increase in concentration from just under 0.03% to the present level of just over 0.04%. Can this small increase have such a profound effect?” 

The science can now provide a much better answer to that question.

We can also now be much more precise about where the additional CO₂ is coming from. Scientists can distinguish fossil-fuel carbon from naturally circulating carbon by examining the isotopic “fingerprint” of atmospheric CO₂. Fossil fuels contain virtually no radioactive carbon-14, because it has decayed away over the millions of years that they have been underground. They are also relatively depleted in carbon-13. By measuring these isotopes in atmospheric CO₂, scientists can identify the contribution from fossil fuels and distinguish it from carbon being exchanged naturally between the atmosphere, oceans and living organisms.

This provides an important independent line of evidence. We are not simply assuming that the additional CO₂ is coming from burning coal, oil and gas because fossil-fuel use has increased at the same time as atmospheric CO₂. The chemical and isotopic fingerprints show that the extra carbon has the characteristics expected of ancient plant material,  precisely what we would expect from fossil fuels. The National Oceanic and Atmospheric Administration notes that these measurements can be used to determine what proportion of CO₂ in an atmospheric sample is derived from fossil fuels.

The important thing is not simply the percentage of the atmosphere occupied by CO₂, but the physical properties of the molecule and its effect on the Earth's radiative balance. CO₂ absorbs infrared radiation at specific wavelengths. Increasing its concentration makes it more difficult for the Earth to radiate energy back into space. The climate system then warms until outgoing radiation once again balances incoming energy. CO₂ does not have to make up a large proportion of the atmosphere to have a significant climatic effect.

Furthermore, we are no longer relying simply on correlations between CO₂ concentrations and temperature. The radiative effect of increasing greenhouse gases can be observed directly. NASA explains that its climate instruments measure how greenhouse gases affect the movement of infrared radiation through the atmosphere, and a 2024 NASA and Jet Propulsion Laboratory study directly measured how increasing atmospheric CO₂ reduces the Earth's ability to emit infrared radiation into space.

Looking back at my 2018 post, I would therefore no longer argue that the human contribution to recent warming is fundamentally uncertain. The evidence is now much stronger that the current rise in atmospheric CO₂ is overwhelmingly the result of human activity, principally the burning of fossil fuels, and that this increase is the dominant cause of the warming observed since the pre-industrial period.

But that does not make CO₂ a “villain” in the conventional sense. It remains an essential gas for life, occurs naturally, and has played an important role in regulating Earth's climate throughout geological history. Nor does recognising the importance of CO₂ mean that all environmental problems can be reduced to carbon dioxide. Conventional air pollutants such as particulate matter, sulphur dioxide and nitrogen oxides remain important threats to human health.

What has perhaps become even more relevant since I wrote the original article is the other side of the argument. If we accept the need to reduce greenhouse-gas emissions, then mining, a major emitter of CO₂, is not the enemy of the green revolution,  it is one of its essential foundations. Wind turbines, solar panels, electricity networks, batteries and electric vehicles all require large quantities of metals and minerals. The energy transition will therefore require more mining, not less (see posting of 10 April 2023).

The scale of the challenge is illustrated by the graphic below. In 2023, the world was still consuming enormous quantities of coal, oil and natural gas, with China and the United States among the largest consumers. Replacing an energy system of this scale is clearly going to be a very substantial undertaking.

Source: elements.visualcapitalist.com

This brings us back to the paradox at the heart of this article. If we accept the need to reduce greenhouse-gas emissions, mining is not the enemy of the green revolution, it is one of its essential foundations. The challenge is not simply to “stop mining”, but to produce the minerals needed for decarbonisation while reducing the environmental footprint and carbon intensity of their extraction and processing.

In that sense, my 2018 article is worth revisiting not because its scepticism about human-caused climate change has been vindicated, but because its underlying question has become even more important: how do we reconcile our environmental ambitions with the enormous material requirements of a modern, low-carbon society?

This is the paradox we should be discussing now. The route to a lower-carbon world runs, at least for the foreseeable future, through a mining industry that itself has to become substantially lower carbon.

#MEIBlog