Aerosol injections to manage European heatwaves?

Question

The heatwave that hit Europe in July was not only highly unpleasant (40°C), but has been predicted to be an exceptionally onerous medical, agricultural and economic burden. As someone outside of the field, I was wondering why attempts involving stratospheric aerosol releases to combat heatwaves in southern Europe are not discussed. The Wikipedia article on stratospheric aerosol injection lists several real, possible and perceived drawbacks, but focuses on it as an impractically expensive global solution as opposed to being used temporarily to reduce heatwaves. Despite extrapolations from a 2006 Californian heatwave test of a reduction of 7°C [ref].

Is the lack of discussion on temporary regional usage of aerosol injection for heatwaves simply caused by non-technical factors like:

• a lack of political willpower (as the Extinction Rebellion protests in the UK and petitions such as this one suggest)
• ethical objections (e.g. we should save wildlife and cut pollution rather than engineer the climate)
• its cost and lack of awareness outside of scientific circles (the aforementioned Wikipedia page is visited only 200 times a day, ten fold less than Snowpiercer, a post-apocalyptic Netflix show with it as a wild premise)
• its experimental state (even if it was tested 16 years ago with some success —as far as I can tell)

Or is the reason technical: from what I understand European heatwaves are caused by anticyclones from Africa (or at least the meteorological offices give these media friendly names like Charon, Scipio or Hannibal) so the solar irradiation was not originally collected in the affected areas (but in the Sahara) so aerosol injections would not work (or worse would trap the heat at night or exacerbate the anti-cyclone)?

What is holding back this option?

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Footnote. there's a related Q here, but it's both unanswered and broad. I am more interested in Europe and heatwaves, hence my opening a new Q.

Answer 1

My question was naïve to the weather dynamics —so the answer is technical: the heat is on the ground, not in the stratosphere.

So there are two things, infrared deflection into space and radiative cooling, wherein heat gets emitted as infrared radiation into space —the two blend into each other, but stratospheric clouds primarily do the former. Given that the hot weather system originated from the south (Sahara) it would be mostly pointless deflecting incoming IR rays, which are not causing the heat in that precise spot. The heat was also on the ground not in the atmosphere, so irradiative cooling up high would be ineffective. After all, on cloudy days during the heatwaves, the temperatures were still well above average during both the daytime and nightime. The nightime detail is because the heat irradiated by the ground via irradiative cooling was being deflected back by the (tropospheric) cloud cover, so in effect an IR mirror is a bad thing as the heat was from the sub but not from there. Similarly, it has recently been proposed that the norther polar vortex (a continuous cyclone that traps the cold in the artic) could be stabilised via stratospheric aerosol injection. Controversies apart, the aim would be to deflect incoming rays, not irradiate stratospheric heat.

There are ground-based technologies that employ radiative cooling (ranging from TiO2 white paint to theoretical nanoengineered panels from IEEE papers). Being more targetted they can be used to tackle the "urban heat island effect" wherein parts of a developed areas can be several degrees higher. So these would be a better safeguard against extreme heatwaves assuming we are unable to rapidly remove 950 gigatons of carbon dioxide by growing new biomass or sequestering it underground.