After the Mount Pinatubo volcano erupted in 1991,

the earth cooled by half a degree Celsius for the next two years.

Should we do something similar, now, on purpose?

The Story in Four Minutes

Nina Grant, Solar Geo Society Ambassador,
PhD Candidate, Rutgers University

There are over a trillion tons of excess CO2 in the atmosphere, and the Carbon Dioxide Removal industry hopes to remove the first billion of those tons over the course of the next twenty years. Nina Grant speaks about the implications.

Our Mission

Solar Geo offers hope that we might cool the planet. Understanding the fundamentals simply requires thinking about the difference between trillions, billions, and millions.

There will always be disagreements over the concept of solar geo (short for solar geoengineering). Our mission is for those disagreements to be better grounded in math and science.

If you wish we could solve
climate change some other way,
you’ve found your home. Because we do, too.

The Ten Numbers

●

The Five
CO2 Numbers

  • One thousand gigatons.

  • It starts as 40 billion tons, but half gets absorbed near ground level by the forests and oceans.

  • At least, until we figure out a way to remove it.

  • This includes trees, grasses, seaweeds, and the like.

  • Some CDR projections are as high as 10 billion tons per year by 2050. Other projections are closer to one billion tons per year by that time.

●

The Five
Solar Geo Numbers

  • Temperatures stayed that way for around two years. You couldn’t notice the difference with the naked eye, but a tiny bit more sunlight got reflected back to space.

  • This sulfur dioxide combined with water vapor to turn into sulfate aerosols, which reflected sunlight.Though largely impossible to notice with the naked eye, this tiny amount of shade was enough to reduce temperatures.

  • This is known as Stratospheric Aerosol Injection. More precisely described in the work of Wake Smith, it is now being referred to as “Polar Solar Geo.”

  • This amount has been gradually decreasing in recent years.

  • Over 5 million people die each year from fossil fuel pollution, according to the British Medical Journal. (Link)

The Five-Minute Counterargument

Raymond Pierrehumbert

Physics Professor
Oxford University

Perhaps the world’s most vocal academic physicist criticizing solar geo

Neil Degrasse Tyson
and Guests

2025 Isaac Asimov Memorial Debate
at the American Museum of Natural History

"The Promises and Pitfalls of Solar Geoengineering”

  • 1. There are over a trillion tons of excess carbon dioxide in the atmosphere.

    Additional Information: Since the pre-industrial era, fossil fuel combustion has emitted well over two trillion tons of CO2, half of which has been absorbed by forests and oceans. For context, a trillion tons is approximately the weight of three million Empire State Buildings.[2]

    References:

    1. NOAA. ESRL Global Monitoring Laboratory - Education and Outreach. 2024. (Link)

    2. NASA. Carbon Dioxide Concentration | NASA Global Climate Change. Climate Change: Vital Signs of the Planet; NASA. February 2024.(Link)

    2. We are making it worse every year by another 20 billion tons.

    Additional Information: This number begins as approximately 40 billion tons, though approximately half is absorbed by forests and oceans. [1]

    References:

    1. Global Carbon Budget. Earth System Scientific Data. December 5, 2023. (Link)

    3. It takes hundreds of years to naturally return to Earth.

    Additional Information: Note that methane has a much shorter life - around 11 years. And it does much more damage, per additional molecule, than carbon dioxide.

    References:

    1. Inman, M. Carbon is Forever. Nature Climate Change. November 20, 2008. (Link)

    2. Buis, A. The Atmosphere: Getting a Handle on Carbon Dioxide. NASA. October 9, 2019. (Link)

    4. The most ambitious global ecosystem restoration plans aim for a few billion tons of additional carbon dioxide removal per year.

    Additional Information: Ecosystem restoration has the potential to remove hundreds of gigatons of additional carbon dioxide over the course of many decades [1,2]. Existing forests hold approximately 861 gigatons of carbon [3], so they must be protected. If burned, they would produce over three trillion tons of additional CO2.

    References:

    1. ‌‌Mo, L., Zohner, C.M., Reich, P.B., Liang, J., De Miguel, S., Nabuurs, G.J., Renner, S.S., van den Hoogen, J., Araza, A., Herold, M. and Mirzagholi, L., Nature. Integrated global assessment of the natural forest carbon potential. November 2023. (Link)

    2. Strassburg, B.B., Iribarrem, A., Beyer, H.L., Cordeiro, C.L., Crouzeilles, R., Jakovac, C.C., Braga Junqueira, A., Lacerda, E., Latawiec, A.E., Balmford, A. and Brooks, T.M., Nature. Global priority areas for ecosystem restoration. October 2020. (Link)

    3. Woodwell Climate Research Center, Global Forest Carbon Storage, Explained, April 17, 2024. (Link)

    5. The Carbon Dioxide Removal (CDR) technology industry, as a whole, aims to draw down its first billion tons of carbon dioxide over the entire course of the next twenty years [1,2,3,4,5].

    Additional Information: The industry targets one billion tons per year by 2050 [5].

    References:

    1. Smith, S. M., Geden, O., Gidden, M. J., Lamb, W. F., Nemet, G. F., Minx, J. C., Holly Buck, Burke, J., Cox, E., Edwards, M. R., Fuss, S., Johnstone, I., Müller-Hansen, F., Pongratz, J., Probst, B. S., Roe, S., Schenuit, F., Schulte, I., Vaughan, N. E. (eds.) The State of Carbon Dioxide Removal 2024 - 2nd Edition, 2024. (Link)

    2. National Academies of Sciences, Engineering, and Medicine; Division on Earth and Life Studies; Ocean Studies Board; Committee on A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington (DC): National Academies Press (US). 7, Ocean Alkalinity Enhancement. December 8, 2021.(Link) 

    3. E. Larson, C. Greig, J. Jenkins, E. Mayfield, A. Pascale, C. Zhang, J. Drossman, R. Williams, S. Pacala, R. Socolow, EJ Baik, R. Birdsey, R. Duke, R. Jones, B. Haley, E. Leslie, K.Paustian, and A. Swan, Net-Zero America: Potential Pathways, Infrastructure, and Impacts, Final report, Princeton University. October 29, 2021. (Link)

    4. My Climate Journey Podcast. “Carbon Management with DOE’s Jen Wilcox.” Recorded October 24, 2023. (Link)

    5. Roads to Removal: Options for Carbon Dioxide Removal in the United States, December 2023, Lawrence Livermore National Laboratory, LLNL-TR-852901. (Link)

    6. Direct Air Capture company 1PointFive website (Link)

    7. New York Times Events, Vicki Hollub - Can an Oil Company Lower Its Emissions? September 24, 2024 (13:21) (Link)

    6. The Earth cooled by approximately 0.5 °C for the two years following the eruption of Mount Pinatubo

    Additional Information: Scientists largely agree that, in 2024, global warming crossed the 1.5 degrees Celsius threshold.

    References:

    1. Newhall, C. The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines, Fact Sheet. 2019. (Link)

    2. Aubry, T.J., Staunton-Sykes, J., Marshall, L.R. et al. Climate change modulates the stratospheric volcanic sulfate aerosol lifecycle and radiative forcing from tropical eruptions. Nature Communications August 12, 2021. (Link)

    7. The 1991 Mount Pinatubo volcanic eruption released approximately 17 million tons of sulfur dioxide.

    Additional Information: This sulfur dioxide combined with water vapor to form sulfate aerosols in the stratosphere, which reflected sunlight for two years, until it settled back to earth.

    References:

    1. Wallace, P. J., & Gerlach, T. M. Magmatic Vapor Source for Sulfur Dioxide Released During Volcanic Eruptions: Evidence from Mount Pinatubo. Science. 1994. (Link)

    2. Bluth, G. J. S., Doiron, S. D., Schnetzler, C. C., Krueger, A. J., & Walter, L. S. Global tracking of the SO2 clouds from the June, 1991 Mount Pinatubo eruptions. Geophysical Research Letters. January 24, 1992. (Link)

    3. Self, Stephen, Jing-Xia Zhao, Rick E. Holasek, Ronnie C. Torres, and Alan J. King, United States Geological Survey, June 11, 1999. (Link)

    8. Scientists discuss potentially dispersing around 10 million tons of sulfur dioxide per year, via a fleet of specially designed planes, in order to approximately match the effects of the Mount Pinatubo eruption.

    Additional Information: This is Stratospheric Aerosol Injection, or SAI. Note that for the sake of simplicity, we address SAI at the Mount Pinatubo level, and not the computer simulations of much greater amounts. Nor do we address the localized strategies of Marine Cloud Brightening (MCB). Detailed analysis in 2024 points to the more specific potential of polar solar geo [5].

    1. Klobas, J. E., et al. "Ozone Depletion following Future Volcanic Eruptions." Geophysical Research Letters. July 6, 2017 (Link) 

    2. Ferraro, A. J., Charlton-Perez, A. J., & Highwood, E. J. Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors, sulfate and titania aerosols. Journal of Geophysical Research: Atmospheres. December 29, 2014. (Link)

    3. David Keith and Wake Smith. Solar Geoengineering Could Start Soon If It Starts Small. MIT Technology Journal. February 5, 2024. (Link)

    4. Sunlight Reflection Management SRM Primer. 2024. (Link)

    5. Smith, W., Bartels, M. F., Boers, J. G., & Rice, C. V. (2024). On thin ice: Solar geoengineering to manage tipping element risks in the cryosphere by 2040. Earth's Future, 12, e2024EF004797. https://doi.org/10.1029/2024EF004797

    9. Approximately 100 million tons of sulfur dioxide are emitted every year in the form of air pollution.

    Additional Information: Note that this sulfur dioxide, at ground level, is especially dangerous to human health. [1,2]

    References:

    1. US EPA. Sulfur Dioxide Basics. June 2, 2016. (Link)

    2. US EPA. Health and Environmental Effects of Particulate Matter (PM). August 30, 2022. (Link)

    3. Zeke Hausfather and Piers Forster. Analysis: How low-sulphur shipping rules are affecting global warming. Carbon Brief. July 3, 2023. (Link)

    4. Eastham, S. D., Weisenstein, D. K., Keith, D. W., & Barrett, S. R. H. (2018). Quantifying the impact of sulfate geoengineering on mortality from air quality and UV-B exposure. Atmospheric Environment, 187, 424–434. (Link)

    10. Over 5 million people die each year from fossil fuel pollution.

    .Reference:

    1. BMJ 2023;383:e077784

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