https://rogerpielkejr.substack.com/p/the-bad-science-and-bad-policy-at
By ROGER PIELKE JR.
Excerpt:
According to Peter Cox of the University of Exeter, most of the planet’s warming this century is not due to greenhouse gases, but reductions in air pollution, mainly sulfur dioxide:
“Two-thirds of the global warming since 2001 is [sulfur dioxide] reduction rather than [carbon dioxide] increases”
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Climate Depot Note: Via Real Scientist:
Clouds have been getting darker and reflecting less sunlight as a result of falling sulphate air pollution, and this may be responsible for a lot of recent warming beyond that caused by greenhouse gases. “Two-thirds of the global warming since 2001 is SO2 reduction rather than CO2 increases,” says Peter Cox at the University of Exeter in the UK.
Some of the sunshine that reaches Earth is reflected and some is absorbed and later radiated as heat. Rising carbon dioxide levels trap more of that radiant heat – a greenhouse effect that causes global warming. But the planet’s albedo – how reflective it is – also has a big influence on its temperature.
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A paper just published — Samset et al. 2025 — arrives at similar conclusions:
[A] time-evolving 75% reduction in East Asian sulfate emissions partially unmasks greenhouse gas-driven warming and influences the spatial pattern of surface temperature change. We find a rapidly evolving global, annual mean warming of 0.07 ± 0.05 °C, sufficient to be a main driver of the uptick in global warming rate since 2010.
The figure above shows that sulfur dixide emissions have decreased over the past several decades at a rate much faster that most IPCC scenarios, and are expected to decrease further this century. Those future reductions will have the effect of increasing average global temperatures.
The fact that air pollution counteracts warming from greenhouse gases has long been understood, and has been discussed in depth in the scientific literature and the IPCC. However, the significance to climate policy of warming resulting from reducing air pollution appears not to have been well thought through.
For instance, Zeke Hausfather explains of planetary warming:
There is around half a degree of warming today that is “hidden” by aerosols. Without the cooling from sulphate and other aerosols, today’s global temperature would already be close to 2C above pre‑industrial levels, rather than the approximately 1.4C the world is currently experiencing.
That implies that the Paris Agreement’s temperature target of 1.5C has already been passed with respect to the warming contributions of greenhouse gases. Further success at reducing air pollution would push the world past the Agreement’s 2C target. For a champion of the UN-FCCC and its Paris Agreement, reducing pollution is thus an obstacle to achieving the treaty’s goals.
There are factors that contribute to changes in global average surface temperature beyond just greenhouse gases. That means that any climate policy focused on temperature targets will inevitably become incoherent — a point that my father has been making for decades — because the UN-FCCC focuses on greenhouse gases as the only climate policy control knob.
The fact that reducing air pollution would have an overall warming effect has long been discussed in the scientific literature. For instance, long-term projections of warming by the IPCC increased between the second (1995) and third (2001) IPCC assessments because of changing assumptions and modeling capabilities related to projected large future reductions in sulfur dioxide emissions. In 2005, Smith et al. argued that as recently as 1990, air pollution counterbalanced almost all increased radiative forcing due to accumulating greenhouse gases in the atmosphere.
The policy incoherence runs much deeper.
Elsewhere, Hausfather argues that the temperature increases caused by reducing air pollution are on balance a “good thing”:
[W]e are rapidly reducing both aerosol emissions and their resulting climate cooling effect. Global emissions of SO2, the most important aerosol, have fallen by 40% since the mid‑2000s. China has cut its SO2 emissions more than 70% over the same period. This is a good thing; SO2 is a major precursor to PM2.5, which is responsible for millions of deaths from outdoor air pollution worldwide.
By this logic, apparently some warming is acceptable.
Instead of “every tenth of a degree increase in global temperatures matters” it is instead “every tenth of a degree matters unless the benefits associated with that increased tenth of a degree are larger than the costs of avoiding it.”
Less catchy, more accurate.
Reducing air pollution has costs as well, but also many benefits. But be careful acknowledging that fact in the context of climate policy, because it turns out that burning fossil fuels also has costs, but is similarly accompanied by many benefits.
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