A Surprising Weapon Against Global Warming
By the middle of the last century, the industrialized nations had caused climate change in the form of global cooling.
Sulfate aerosol emissions were the big factor there, coming from, for instance, burning fossil fuels.1“Why did climate cool in the mid-20th Century?” Skeptical Science, 16 October 2016 And this was enough to hold greenhouse warming at bay.2Bauer, S.E., Tsigaridis, K., Faluvegi, G., Kelley, M., Lo, K.K., Miller, R.L., Nazarenko, L.S., Schmidt, G.A., & Wu, J. (2020). Historical (1850–2014) Aerosol Evolution and Role on Climate Forcing Using the GISS ModelE2.1 Contribution to CMIP6. Journal of Advances in Modeling Earth Systems, 12.
But then we ramped down on aerosol emissions because of air pollution, acid rain, etc. Also we ramped down on chlorofluorocarbons (CFCs) to save the ozone layer (and it’s working).
But we continued to generate greenhouse gases at a high enough rate that the removal of the cooling offset resulted in our recent trend of global warming.
The decrease in human-caused aerosols may have also contributed to an increase in tropical storm frequency in the Atlantic basin since the 1970s.3Knutson, T. “Global Warming and Hurricanes: An Overview of Current Research Results.” GFDL, Oct. 24, 2022.
The United States has taken the belt-and-suspenders strategy to fund a 5-year research plan to…you guessed it…spew aerosols into the air to get things cooling down again.4Tran, T. H. “The White House Admits It: We Might Need to Block the Sun to Stop Climate Change.” Daily Beast. Nov. 18, 2022
The report will be dedicated specifically to a form of geoengineering known as solar radiation management. This is a technique that essentially involves spraying fine aerosols into the atmosphere to reflect sunlight away from the Earth. The idea is that, once it’s reflected, there’ll be less heat and temperatures will go down.
If this was a movie, a character at this point would say something like “That’s crazy enough it just might work!”
According to Professor Emeritus Stephen Salter5Salter, S. H., Stevenson, T., & Tsiamis, A. (2014). CHAPTER 6. Engineering Ideas for Brighter Clouds. In Geoengineering of the Climate System (pp. 131-161). (Geoengineering of the Climate System). Royal Society of Chemistry. https://doi.org/10.1039/9781782621225-00131:
It may be possible to reduce global warming by increasing the reflectivity of marine stratocumulus clouds thereby reducing the amount of solar energy that is absorbed. Quite a small change to the reflectivity could stop further temperature rise or even produce a reversion towards pre-industrial values.
The Salter mechanism for “cloud brightening” would be via a fleet of “mobile spray vessels” releasing sub-micron drops of sea water into the marine boundary layer.