Sulphur dioxide decline adds to global heating

 From Leon Simons

As more and more clean air regulations came into effect from the 1960s onward, CO₂ and sulphur dioxide (SO₂) emissions gradually decoupled. SO₂ emissions reached a global peak around 1980: academic.oup.com/bioscience/a...

There was an almost perfect correlation between CO₂ and SO₂ emissions. But this has turned into a strong anti-correlation:

 

This was made possible by strict clean air regulations, enforcement and compliance. Notably at coal plants, where enormous 'flue-gas desulphurisation systems were installed. The increase in sulphur emissions temporarily stopped global warming for about 40 years:

But it's crucial to take into account where the sulphur is emitted. While the oceans "only" cover about 71% of Earth's surface, about 90% of global warming is ocean warming, while only 1-2% heats the atmosphere:

 

Removing the reflective particles and clouds above the oceans (Earth's main heat sink!) has much stronger climate impacts than most realise. Which is why the very recent desulphurisation of global shipping is crucial to take into account. The IMO [International Maritime Organisation]sulphur regulations made this possible. And there are more regulations in the pipeline! 

Leon Simons notes that the rise in SO2 emissions before 1900 seems suss, and discusses
it in his Bluesky thread (linked above)

Back in 1990, Hansen & Lacis described an "extreme" scenario of half the GHG [Greenhouse gas] forcing being compensated by a negative aerosol forcing. Looking at the same agents, IPCC AR6 WG1 showed it as 66% for the 1850-1989 period. It was likely even more!

The moral of all this is obvious:

1.  With industrialisation taking off post-war, rising SO2 emissions helped offset rising CO2 emissions, and global temperatures actually fell.
2. After 1980, SO2 emissions started to fall, and temperatures started to rise.
3. Since 2020, de-sulphurisation of global shipping has increased, reducing reflective particles and clouds above the oceans, leading to accelerated global temperature rise.

I draw two other conclusions:

1. It is not essential to emit SO2 at great altitudes, as with, say, volcanic emissions or (shudder) geo-engineering for it to cool the planet.  A couple of hundred metres above sea level is enough.
2. The science behind global heating is confirmed.  From Hansen onwards, climate models postulated that SO2 emissions would reduce temperatures, while CO2 emissions would increase them.  This has now been clearly demonstrated by the surge in temperatures as SO2 emissions have been reduced.  The phenomenon of reduced cloud cover (leading to faster heating) is also explained.  The model is consistent.

What is less obvious is what we do about it.  Should we allow global shipping to go back to emitting sulphur dioxide?  Should we deliberately try some sort of geo-engineering fix?  Do we want to go back to acid rain?

No doubt big oil will argue for increased emissions of SO2 with the same vigour it tried to shut down the argument for reducing emissions of CO2, even though the effects on temperatures are derived from the same physics.  Look out for articles funded by stink tanks arguing for SO2 emissions paid for by the taxpayer.