As I explained in an article posted last January (“More Evidence for Extreme Climate Stability“), comprehensive marine temperature proxy measurements have removed any doubt that global warming over the past 75 years is real (see figure).1 These measurements show that from 900–1900 AD global mean ocean surface temperatures remained constant to within ±0.06°C. However, from 1900 AD to the present the global mean ocean surface temperature has risen by 1.10°C.
Are we headed for catastrophe? Not necessarily. In this post, I’ll review various geoengineering proposals to offset warming that hold promise but also come at a cost.
Figure: Global Mean Marine Surface Temperature Change since 900 AD Adapted from figure 2 of Osman et al., Nature 599 (2021): 241, and from figure 1 of Marcott and Shakun, Nature 599 (2021): 208.
Climate Change Mitigation Goals Recently, the United Nations Intergovernmental Panel on Climate Change (IPCC) has issued dire warnings about the rapidly rising global mean temperature. They point out that in spite of admirable efforts to reduce greenhouse gas emissions, Earth’s increasing wealth, technology, and population are causing atmospheric greenhouse gas levels to continue to rise. While there’s been some reduction in the amounts of chlorofluorocarbons in the atmosphere, carbon dioxide, methane, and nitrous oxide levels have all increased.
In 2015, the IPCC set a goal of ensuring that the global mean temperature during the twenty-first century rises by no more than 1.5°C above the pre-industrial level. For this goal to be attainable, they calculated that greenhouse gas emissions would need to peak by no later than 2025. Any increase beyond 1.5°C, they determined, would have catastrophic economic and social consequences for at least half the world’s population. Some of the worst consequences include reduced crop yields and heat stroke deaths in tropical cities, major droughts and floods, extreme weather events, increased wildfires, and rising sea levels.
Participants in the United Nations Climate Change Conference held in Egypt, November 6–18, 2022, commonly referred to as COP 27, stated, “The world still needs a giant leap on climate ambition,”2 At the conference’s outset, UN Secretary-General António Guterres said humanity is “on a highway to climate hell with our foot still on the accelerator.”3 The COP 27 participants noted that progress toward the IPPC’s stated goals in 2015 has been so minimal that it seems hopeless that they’ll ever be achieved.
The previous claim that wind and solar energy production could quickly replace the need for generating energy through fossil fuel burning appears impractical, if not impossible. To completely replace fossil fuels, wind turbines and solar panels would need to carpet many millions of acres. For example, to provide for the total energy consumption of the US human population in 2020 would require solar panels covering about a hundred thousand square miles. Such carpeting will inevitably harm ecosystems. Furthermore, maintaining, replacing, and recycling wind turbines and solar panels bring on ecological problems that remain unsolved.
Geoengineering Proposals Growing pessimism about the adequacy of so-called green alternatives to generating energy through fossil fuel burning has motivated engineers to propose geoengineering Earth’s stratosphere to partly block out the Sun’s heat. On October 13, 2022, the White House announced that the federal government would fund a five-year research study on technologies and innovations to artificially modify Earth’s climate.
Aerosol Pumping The most popular geoengineering proposal calls for pumping sulfur dioxide particles and/or sulfate aerosols into the stratosphere. This proposal copies the natural phenomenon of volcanic eruptions and, therefore, currently ranks as the best-understood and tested geoengineering proposal. Major volcanic eruptions in the past, like the Krakatoa eruption in 1883, pumped huge quantities of sulfur dioxide and sulfate aerosols into the stratosphere.
The Krakatoa eruption so increased cloud reflectivity that for the year following the eruption Earth’s surface was cooled by as much as 0.4°C. However, the sulfur compounds that were pumped into the atmosphere eventually fell to the ground as acid precipitation.
A research team led by Caspar Ammann used a coupled Atmosphere-Ocean General Circulation Model to establish that greenhouse gas-countering anthropogenic forcing, sufficient to bring the global mean temperature down to what it was in 2000, would need to be much larger than anything experienced from volcanic eruptions.4 Their model showed that most, but not all, of Earth’s continental landmasses would experience substantial cooling, but that there would be minimal reductions in sea ice loss.
Sulfur Dioxide Injection Another research team used six different Earth system simulation models to determine results from the continual injection of 5 teragrams of sulfur dioxide per year into the stratosphere between 2020 and 2069.5 The team found that this 50-year period of sulfur dioxide injection would compensate for 50 gigatonnes (55 billion tons) of carbon injected into the atmosphere from the burning of fossil fuels. Currently, fossil fuel burning injects 8.7 gigatonnes/year of carbon into the atmosphere.
Stratocumulus Cloud Modification Three atmospheric physicists have proposed a less invasive geoengineering solution to global warming. They present a study of the climate response to deliberately seeding large-scale stratocumulus cloud decks in the North Pacific, South Pacific, and South Atlantic Oceans.6 They use a fully coupled atmosphere/ocean version of the Met Office Hadley Center computer model to show that up to 35% of greenhouse gas emissions from current human activity could be offset by stratocumulus cloud modification.
White Urban Surfaces Three Canadian environmentalists suggested an even less invasive proposal. They used a global climate model to determine the impact of replacing urban surfaces with high solar reflectance materials.7 They showed that if all urban rooftops and pavements were white-colored, a global cooling of as much as 0.07°C could be achieved, which is equivalent to a carbon dioxide emission reduction of 150 billion tonnes. While this achievement seems relatively modest, the environmentalists explained that the light-colored urban surfaces would reduce air-conditioning usage, which would mitigate the urban heat-island effect and reduce fossil fuel consumption.
Calcite Injection Atmospheric physicist David Keith noted that injecting sulfate aerosols or sulfur dioxide into the stratosphere results in stratospheric ozone loss. Such loss would allow more harmful ultraviolet radiation to reach Earth’s surface. This radiation would diminish crop and forest production and increase human cancer and respiratory disease rates. Therefore, Keith proposes injecting calcite (calcium carbonate) particles into the stratosphere instead of sulfate aerosols or sulfur dioxide particles.8 He determined that injecting calcite into the stratosphere would augment the stratospheric ozone by 4% while delivering 10 times more cooling to the lower stratosphere than what would be achieved by injecting sulfate aerosols into the stratosphere.
Solar Shields One radical geoengineering proposal recommends installing a solar shield permanently positioned between the Sun and Earth. It’s the only geoengineering proposal, so far, where the amount of Earth cooling could be precisely regulated without any time delays. Such a shield or combination of shields could be designed to constantly adjust the amount of solar radiation incident on Earth’s surface. Such shields must be equipped with propulsion systems to keep them optimally positioned between the Sun and Earth. Solar panels attached to the shields could provide the energy needed for the propulsion systems.
Geoengineering Benefits and Dangers Atmospheric carbon dioxide stimulates photosynthesis. For atmospheric carbon dioxide levels above 400 parts per million, rising atmospheric carbon dioxide levels hinder respiration.9 The optimal atmospheric carbon dioxide level for crop, tree, and plant productivity is 600–650 parts per million. However, photosynthesis is also temperature-dependent. Photosynthesis rates peak at 18°C (64°F) and 28°C (82°F) for C3 (trees, shrubs, wheat, rice, barley, rye, millet, and oats) and C4 (corn and sugar cane) plant systems, respectively.10 Most of the world’s vegetation is already at or beyond the optimal photosynthesis temperatures.
The only way crop, tree, and plant productivity can be enhanced through increased atmospheric carbon dioxide is if the global mean temperature is reduced. Injecting huge amounts of sulfate aerosols, sulfur dioxide particles, and/or calcite particles into the stratosphere can potentially achieve that goal. However, such geoengineering means that there would be less sunlight available for photosynthesis. The end result may well be a net zero enhancement of photosynthesis. That is, there may not be an uptake of carbon dioxide consumption by plants.
An enormous benefit of stratospheric, space-based, and/or stratocumulus cloud geoengineering is that it could halt the melting of the polar ice cap and of icefields in Antarctica, Greenland, the Tibetan Plateau, and the high mountain ranges of the world. An even greater challenge facing humanity than global warming would be the onset of the next ice age.
As I explain in my book, Weathering Climate Change, any substantial melting of the winter polar ice cap would bring on the next ice age just like it has in all previous ice age cycles.11 Arctic ice reflects sunlight with about 60% efficiency. Open Arctic liquid water reflects sunlight with only 6% efficiency. The extra solar heat absorbed by the Arctic with a reduced winter ice cap will produce more water vapor which will fall as extra snow on Canada, Greenland, northern Europe, and Siberia.
Though the IPCC and other scientific and political consortiums have expressed concern about the dangers of rising sea levels from the increased melting of Earth’s ice, the bigger concern is the aforementioned onset of the next ice age. Geoengineering proposals may delay that onset with the proviso that the geoengineering is adopted quickly.
Geoengineering Economic Costs Space-based geoengineering holds a promise for the greatest benefits. However, it is by far the most costly of the geoengineering proposals. Even a bare minimum effective set of solar shields would cost at least 10 trillion US dollars. Most scientists believe that this minimal cost would be greater than accepting the financial consequences of ongoing global warming.
The expense of injecting adequate amounts of sulfate aerosols, or sulfur dioxide, or calcite particles into the stratosphere to bring global warming to a halt is not unreasonable. Using only existing US military aircraft, annual costs would be just several billion US dollars. Using balloons, artillery, or rockets to loft the aerosols and/or particles would be more expensive. Attempts to pump up the aerosols or particles through hoses attached to balloons or towers atop high mountains would be even more costly.
The costs of seeding stratocumulus clouds and covering urban surfaces with more reflective paints certainly will be lower than stratospheric geoengineering projects. However, even in combination, stratocumulus cloud seeding and painting of urban surfaces will offset only a small fraction of current greenhouse gas emissions.
Geoengineering Uncertainties The dangers and risks of geoengineering are many and in some instances serious. For all geoengineering projects, with the exception of painting urban surfaces, there would be less sunlight for solar power generation and for photosynthesis. With stratospheric geoengineering, the skies would no longer be blue and astronomical observations through ground-based optical telescopes would be severely hampered, if not rendered impossible. Satellite remote sensing would be negatively impacted as well.
None of the geoengineering proposals would do anything to stop the acidification of oceans, lakes, and rivers from greenhouse gas emissions. Stratospheric geoengineering based on sulfate aerosols and sulfur dioxide particles would make the acidification of oceans, lakes, and rivers much worse. Sulfur compounds injected into the stratosphere eventually return to Earth’s surface in the form of sulfuric acid or other sulfur-based acids.
Geoengineering, with the exception of solar space shields, will not produce uniform surface temperature reductions. There will be major regional disparities in the degree of temperature compensation and major regional differences in precipitation changes.12 Some regions will become wetter and will experience major flooding events. Other regions, especially northern South America (including the Amazon), the Indian subcontinent, the Middle East, North Africa, and most Mediterranean regions will experience catastrophic decreases in precipitation.13
In no case has the degree of temperature and precipitation alterations or the locations of the alterations been accurately determined. Furthermore, all computer simulations of stratospheric geoengineering—where the geoengineering runs for more than three decades—show that if or when the geoengineering ceases, a very rapid global warming of at least a few °C occurs. For these reasons alone, stratospheric geoengineering is not an acceptable option.
Does the inadequacy or unacceptable expense of geoengineering mean that humanity is doomed to face dire consequences? Not at all. I’m convinced that our Creator has not left us bereft of solutions. In next week’s post, I’ll discuss options to geoengineering that can mitigate global warming and climate instability while boosting the world economy, especially for the benefit of the world’s poorest people.
Caspar M. Ammann et al., “Climate Engineering through Artificial Enhancement of Natural Forcings: Magnitudes and Implied Consequences,” Journal of Geophysical Research: Atmospheres 115, no. D22 (November 27, 2010): id. D22109, doi:10.1029/2009.JD012878.
Maxime Plazzotta, Roland Séférian, and Hervé Douville, “Impact of Solar Radiation Modification on Allowable CO2 Emissions: What Can We Learn from Multimodel Simulations?” Earth’s Future 7, no. 6 (June 2019): 664–676, doi:10.1029/2019EF001165.
Andy Jones, Jim Haywood, and Olivier Boucher, “Climate Impacts of Geoengineering Marine Stratocumulus Clouds,” Journal of Geophysical Research: Atmospheres 114, no. D10 (May 27, 2009): id. D10106, doi:10.1029/2008JD011450.
Hashem Akbari, H. Damon Matthews, and Donny Seto, “The Long-Term Effect of Increasing the Albedo of Urban Areas,” Environmental Research Letters 7, no. 2 (April 12, 2012): id. 024004, doi:10.1088/1748-9326/7/2/024004.
David W. Keith et al., “Stratospheric Solar Geoengineering without Ozone Loss,” Proceedings of the National Academy of Sciences USA 113, no. 52 (December 12, 2016): 14910–14914, doi:10.1073/pnas.1615572113.
Astrid C. Wittmann and Hans-O. Pörtner, “Sensitivities of Extant Animal Taxa to Ocean Acidification,” Nature Climate Change 3 (November 2013): 995–1001, doi:10.1038/nclimate1982; Hugh Ross, “Complex Life’s Narrow Requirements for Atmospheric Gases,” Today’s New Reason to Believe (blog), Reasons to Believe, July 1, 2019.
Katharyn A. Duffy et al., “How Close Are We to the Temperature Tipping Point of the Terrestrial Biosphere?” Science Advances 7, no. 3 (January 13, 2021): id. eaay1052, doi:10.1126/sciadv.aay1052.
Ben Kravitz et al., “A Multi-Model Assessment of Regional Climate Disparities Caused by Solar Geoengineering,” Environmental Research Letters 9, no. 7 (July 22, 2014): id. 074013, doi:10.1088/1748-9326/9/7/074013.
K. Karami et al., “Storm Track Changes in the Middle East and North Africa under Stratospheric Aerosol Geoengineering,” Geophysical Research Letters 47, no. 14 (July 28, 2020): id. e86954, doi:10.1029/2020GL086954; Jones, Haywood, and Boucher, “Climate Impacts of Geoengineering.”
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