by Sanjana Kulkarni
figures by Jovana Andrejevic

The average global temperature is increasing faster now than at any time in the last 2 million years. This has fueled record-breaking droughts, heat waves, and wildfires, and has intensified weather patterns, causing more extreme and damaging hurricanes and rainfall. Human activity is driving this change, primarily through the emission of carbon dioxide (CO2) and other greenhouse gases, which are released when fossil fuels like coal, oil, and natural gas are burned to produce energy. 

When sunlight strikes the Earth’s atmosphere, around 30% of it is reflected back out to space, and 70% is incorporated into the climate’s energy system. The Earth radiates some of this absorbed heat out to space, but greenhouse gases in the atmosphere prevent it from escaping. Greenhouse gases are necessary to keep the planet warm enough for living things, but very high concentrations are increasing global temperatures beyond the normal range (Figure 1). Although the best way to slow climate change is to reduce greenhouse emissions by switching to clean energy sources like solar, wind, water, and nuclear energy, the CO2 already in the atmosphere can persist and continue to exert warming effects for centuries. Geoengineering, the large-scale modification of Earth’s climate, is worth exploring because countries have been cutting their emissions too slowly to make any near-term impact on climate change.

Figure 1. The Greenhouse Effect: Incoming sunlight is partially reflected but mostly absorbed by the Earth. Some of the heat absorbed by the Earth is radiated out to space, but greenhouse gases act like a blanket and trap the heat, increasing the planet’s average temperature. Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor are all greenhouse gases. CO2 is a stable atmospheric gas, and its warming effects persist for decades. 

Giving Earth Some Shade

The greenhouse effect increases the amount of sunlight that the Earth absorbs, thereby heating the planet. To counter this, several methods have been proposed to cool the Earth by reducing the amount of sunlight that reaches the Earth in the first place. These light reflecting methods are collectively called solar geoengineering. One method involves spraying tiny particles called sulfate aerosols into the atmosphere to reflect away sunlight. Sulfate aerosols are naturally released from volcanoes and desert dust. They are also produced by burning fossil fuels and actually offset a portion of global warming caused by greenhouse gases. However, when released at ground level during fossil fuel combustion, they cause dangerous levels of air pollution. Scientists are experimenting with releasing sulfate aerosols into the stratosphere using airplanes or hot air balloons, where the aerosols can effectively increase sunlight reflectance but are too high to cause dangerous air pollution levels (Figure 2).  

The main advantages of this method are speed, reversibility, and relative cost-effectiveness, as it is estimated to cost $2.5 billion per year. Additionally, sulfate aerosols are relatively well studied because they already exist in the atmosphere. However, the stratosphere contains a layer of ozone, a gas that absorbs the most harmful types of ultraviolet radiation from the sun, and it’s possible that sulfate aerosols could initiate ozone-destroying reactions, allowing more ultraviolet rays to reach the Earth.

Another cooling method involves brightening clouds above the oceans. In general, darker objects absorb light while brighter objects reflect it. Brightening clouds above oceans would cause the clouds to reflect more light away before it can be absorbed by the dark oceans below. A cloud’s brightness depends on the size of the water droplets that comprise it (smaller droplets have more surface area, so they scatter more light and appear brighter). To brighten clouds, tiny seawater aerosols could be sprayed over the oceans, so that small water droplets form around them. The smaller the aerosols, the smaller the droplets that stick to them. However, changing the droplet size could also affect how long the clouds last and how much water they can hold. Because clouds form in the lowest level of the atmosphere, called the troposphere, cloud brightening has a greater risk of affecting weather patterns than spraying sulfate aerosols high into the stratosphere.

Figure 2. Atmospheric Layers: The Earth’s atmosphere is comprised of five distinct layers. The troposphere, the closest layer to the Earth’s surface, is where weather occurs. Because clouds are found in the troposphere, cloud engineering occurs here too. The next layer is the stratosphere, which contains the ozone layer and is where commercial airplanes fly. Light-reflecting sulfate aerosols can be sprayed into the stratosphere to avoid polluting the tropospheric air that we breathe. 

Cloud brightening requires more investment up front to build the machines necessary to take in seawater, convert it to tiny droplets, and spray them into the air. The machines would likely be carried on boats to move to different parts of the ocean, but they must be able to withstand strong ocean currents and weather conditions. The estimated cost of building a large enough fleet of these boats is $3-5 billion, in addition to ongoing maintenance costs. 

The primary knowledge gap of solar geoengineering is in how rapid sunlight changes will affect other aspects of climate besides temperature. This can be studied in climate models, but it is difficult to test in the real world. There is also concern that the drop in sunlight may decrease plant growth, thereby increasing the amount of atmospheric CO2 and reducing crop yields. These methods also fail to address the root cause of climate change.

Engineering the Oceans

Another major problem of too much CO2 in the atmosphere is ocean acidification, which occurs when CO2 dissolves into the ocean and makes carbonic acid. Acids dissolve the hard shells of many ocean animals like corals, killing them. Additionally, many animals without shells are also sensitive to changes in acidity and can’t survive outside a narrow range. Another problem with high ocean CO2 concentration is that it causes even more CO2 to accumulate in the atmosphere. Oceans currently absorb 25% of the CO2 that humans release into the atmosphere, but oceans are reaching a limit and are not able to absorb as much CO2 as before. 

Ocean fertilization is the best studied ocean geoengineering method and may be able to reduce both ocean acidification and global warming. It involves supporting the growth of phytoplankton, which convert CO2 into oxygen through photosynthesis. Microscopic phytoplankton perform around 50% of the world’s photosynthesis. Just like fertilizer can be added to gardens to help plants grow faster, different fertilizers can be added to oceans to help phytoplankton grow faster and consume more CO2. Iron is the main ocean fertilizer under consideration, and this process would be much cheaper and faster than planting more trees on land.

However, there are potential unintended consequences of this method. Overgrowth of phytoplankton could cause algae blooms that deplete oxygen from water, thereby harming marine animals. Additionally, although phytoplankton are crucial at the bottom of the marine food chain, a sudden increase in their population may shift the balance of different algal species, destabilizing the marine ecosystem. This is also more expensive, less efficient, and will take longer to set up than aerosol methods. The cost depends on the type of nutrient (iron or other) added to the ocean, but the average annual estimate is $450 billion.

Direct Carbon Capture

Direct carbon capture is an umbrella term for chemical reactions that filter CO2 from the air. Existing technology can store CO2 underground or funnel it to be used to make consumer goods. Carbon capture has fewer risks than the other methods, and it addresses the root problem of excess atmospheric CO2, but it requires more work upfront to research different techniques and build the necessary infrastructure than solar geoengineering. 

Carbon capture methods have facilitated growth of a market for carbon trading, and several companies, such as Carbon Engineering, Global Thermostat, CarbonCure, and Climeworks have been working to commercialize their technologies. As opposed to the other methods, the costs of developing these technologies will most likely fall to the private sector, whereas public investment will be in the form of monitoring and regulation.

Figure 3. Summary of Geoengineering Methods: Many other geoengineering methods are being researched and explored, but the primary ones are shown here. Geoengineering is divided into solar geoengineering (reflecting sunlight to cool the planet) and carbon capture (removing CO2 from the atmosphere to slow greenhouse effect-induced warming).

Geoengineering for the World

The primary challenges of geoengineering are conducting field experiments to accurately assess potential consequences and developing international agreements to safely deploy and monitor geoengineering technologies. If geoengineering were adopted, a combination of techniques would be used depending on cost, regional conditions, and the climate’s response. Different methods may have local or global effects, so regulatory policies need to be agreed upon by the international community. Therefore, many scientists have called for the creation of regulatory agencies to advise the United Nations and lay out plans for how geoengineering methods should be prioritized. Geoengineering could help us reverse climate change in a more controlled manner, buying us time to make our society more sustainable.

Sanjana Kulkarni is a first-year Ph.D. student in Virology at Harvard Medical School

Jovana Andrejevic is a fifth-year Applied Physics Ph.D. student in the School of Engineering and Applied Sciences at Harvard University

Cover image by cocoparisienne on Pixabay

For More Information:

  • To read more about geoengineering, check out How to Cool the Planet by journalist Jeff Goodell and The Planet Remade by science writer Oliver Morton.
  • Check out many other geoengineering methods not discussed in this post here
  • For a good summary about the lack of geoengineering research and the challenges of implementation, see this Nature article.
  • For information about geoengineering research being conducted at Harvard, check out the Solar Geoengineering Research Program and the development of controlled stratospheric experiments
  • To learn more about ocean acidification and buffering, see this Nature Scitable article.
  • For more information on global warming and its impacts on humans and other organisms, see journalist Elizabeth Kolbert’s writings.

65 thoughts on “Reversing Climate Change with Geoengineering

  1. How about we leave the planet alone the planet has dealt with way more CO2 than we could ever dream of CO2 is barely at .03% which it was much higher up to 50% more during Palaeozoic when the Meganisoptera strived, (we know this because of petrified Amber , which is trees sap, and they have bubbles in them, and they would extract the air from the bubbles.) They had an exoskeleton so nowadays they would suffocate because of how big they were. CO2 is not the issue it’s never been the issue. Lowering CO2 below .02% will kill plants. What controls the climate is the earths tilt (Milankovitch (Orbital) Cycles) during the Roman Empire is when we were at Max tilt for the heat which is 24.1° now we are at 23.3° moving towards the ice age which is 21.4° during the Roman Empire deserts would get up to 200 degrees Fahrenheit now our deserts get up to about 150 degrees Fahrenheit It takes 100 years for the tilt to change .1 degree what you are doing is dangerous and stupid but you get a lot of money from the government so you’re not gonna stop, but it is against the Nuremberg code and people are not stupid. They will figure out what you’re doing. But it’s a good thing. You have a bunch of people lying like the media. That’s also paid by the governments so that we can live ignorantly while you damage the youth with the chemicals. Sorry for my terrible punctuation.

  2. There is no such thing as climate change is fictitious and was created to create fear. The Earth is going through natural changes, and by analyzing the course of ice taken from Iceland deep within a lake you can see the pattern. Geo engineering the weather as you all well know causes harm to the public to earth and to our oceans, and it is intentional that you were harming all of it. Give us some credit to know the difference. Do you think we’re all ignorant? The Lord sees all.

    1. Susan I agree with you 100%! What they are doing is spaying everything with dangerous chemicals I haven’t seen the sun for 2 months at least. I live in Michigan and they spray our sky every day, and at night. I am sure it’s to hurt the people it has nothing to do with global warming, that’s my opinion. All people have to do is look at the sky.

    2. “THEY” ARE CAUSING “Climate Change” by destroying our ozone with all of the chemicals sprayed globally constantly!!!
      THIS IS 100% A SPIRITUAL WAR!!! Earthly weapons will NOT work this time! Please WAKE UP!! ⏰️ 🙏✝️☝️❤️

  3. Geoengineering unfortunately is now “climate profiteering” The dumping of everything into our atmosphere is causing our weather and climate to go out of control. They thought they could put particles in the air to reflect the Sun away, it’s not working, the particles come down to earth. They’re mixing on the ground with things like brake dust which are also nanoparticles then these particles are turning brown and black and now they’re going back up in the sky and they are actually making climate change worse. Did they not teach these kids about gravity. Then they want to put up clouds to block out the sun unfortunately that causes a greenhouse effect again causing the temperatures to increase. There is a simple answer to reverse climate change we all watched it during the pandemic it actually works, it’s called not burning fossil fuels. If everybody remembers 6 months into the pandemic traffic was back on the roads and we still didn’t have a lot of smog over the cities and you know what that answer is, how that happened, and why that was, it is because the airlines didn’t start flying until nearly a year and a half later. I’m so tired of people telling me the airlines don’t pollute. It’s a gas powered engine, you can call it jet fuel, car fuel, boat fuel, I don’t care what kind of fuel you want to call it, it’d a gasoline powered engine and they pollute, and with the number of jets in the sky they cause nearly as much carbon pollution as the cars on the ground. So until we get some professors that can actually teach these students what the real problem is, and look at ways to remove the carbon from the earth, rather than polluting it with more garbage which is making everything worse, we’re screwed!
    I live in the deserts of Southern California and geoengineering is so out of control here! the massive particle dumps actually got into our homes and it made people sick, people had to leave their homes, and now you have a bunch of people walking around talking about shooting pilots and blowing up airports….we have a problem.
    I want to repeat this so everyone knows, we need to look at removing carbon from the air without adding more pollutants to the air because that is not the answer, that is the wrong way to go about this.
    When you add stuff to the air it attracts people that want to make money, that want to invest money, to make a lot of money, they want to invest money into something that is continuous, so they make lots of money, and that’s where we’re at!!! We now have a bunch of billionaires investing in in what is now a trillion dollar business and we need to stop this before it’s too late! Has anybody thought about building an office building in the middle of a city that would actually be like a gigantic air purifier with fans bringing the air in to a system that all went to the bottom and then came up through water in the top removing the carbon and then releasing clean air out of the top? Maybe figuring out a way to take volcanic ass and use it to make large square Shields that would attract carbon in cities rather than just sprinkling it in the air where people are getting exposed to it.

  4. We already have been geoengineering for centuries – we just need to get better at it. It honestly should not be difficult.

  5. So you think you have enough intelligence to save us from our climate woes? What’s you’ve done to date Is more than questionable. And for starters, would you please cease it with the chem trails which I have been watching for years as you turn beautiful blue skies to a milky white. All I fear as a result of your misplaced, sick and reckless experiments is a dead, uninhabitable planet. But, in your infinite wisdom, remember one thing – it’s not nice to fool Mother Nature.

  6. I don’t worry about all the preceding theories and all have a bit of truth to them. I know plants adsorb CO2 and give off oxygen. GOD takes care of that. GOD took care of some people (Noah) that deviated from his directions for peaceful living. People writing opinions sound as if they are going to live a thousand years and they are theorizing how we can save ourselves in/from the future.
    Our concerns aren’t going to amount to much except all of us will pay more taxes to help the greedy politicians have their next election win. Remember “Henny Penny”? “The sky is falling” I’ll not worry–I’ll be in Heaven. You will also if you believe in Jesus.

    1. The interesting thing is that Greedy Billionaires And politicians are ignoring the fact that the wealth gap, income inequality, global warming is increasing crime, drug addition And the Mental Health Crisis according to sociology. The reality is that the money is not going towards housing, high speed rail infastructure, nuclear or even Universal Childcare. So, The Capitalist bourgeoisie worsening global warming, socioeconomic crime rate and poverty seems to be more of a problem interesting enough. What is actually the problem is that the Capitalist ruling class has our taxpayer go towards Wall Street rather than universal healthcare, walkable cities, Special Education, or fighting global warming. The interesting thing is that I do not recall the Bible saying anything about taxes.

  7. It’s a very slick presentation, but I think it’s dishonest to ignore ongoing chemical spraying that has been taking place for decades. To me these high minded academic “ideas” are like fixing the problem with more of what caused the problem in the first place. We put too much exhaust in the air we breathe so let’s put more chemicals to capture the carbon or block the sun from overheating the earth. At some point nature must balance the forces on a planetary scale and that process could involve losing our habitat, the life of earth. Perhaps we’re reaching that point as the food web disappears and we lose enough forests and plankton to deprive the stratospheric ozone layer of input oxygen, much less having enough (steadily depleting) atmospheric oxygen to breathe.

    1. This is EXACTLY what has sped up climate change at a drastic pace. We are waking up on a global level and will hold those accountable!!!
      Please take a look at my site, and feel free to reach out. I am looking to build a class action lawsuit regarding weather modification/geoengineering, and 5G!

      1. In conclusion, the discussion around 5G as a significant human health risk in the peer-reviewed literature was initially largely driven by authors from, or with links to, various campaigning organizations and linked publications directly to appeals for a moratorium on 5G. Commentaries and letters are personal opinions and are rarely based upon a methodological appraisal of the evidence, but the narrative of the initial period covered in the current review, relied mostly on reviews of lower methodological quality compared, with the subsequently published reviews by independent researchers and researchers with links to industry. It is likely that articles in the popular media, therefore, were influenced more heavily by the initial advocacy publications than by the later higher quality contributions. Importantly, there is no clear answer (yet) whether the resulting narrative from the peer-reviewed literature describes an overestimation of risks as a result of articles with links to campaigning organizations, or whether later contributions from authors with links to industry, and possibly most independent authors, at the latter stages of the critical window describe an underestimation of true causal associations, or whether their combined evaluation will inform future evidence synthesis closer to “the truth”. It is, however, well established that not including explicit evaluation of the quality of studies included in evidence synthesis, and which was most evident in publications classified as “activism”, makes such reviews more susceptible to biased inferences. In addition to issues related to controlling the narrative and the impact of “white hat bias”, the current work further describes undisclosed non-financial CoIs that are likely to have influenced the interpretation of evidence. This was also observed particularly for those publications associated with campaigning organizations. The narrative around 5G and potential human health effects should be interpreted through this lens, in particular because many of the authors with links to various campaigning organizations in this article (Hardell, Héroux, Miller, and Moskowitz) as well as others who published works after the covered period have recently joined up formally in a new advocacy group ICBE-EMF (27).

      2. The primary challenges of geoengineering are conducting field experiments to accurately assess potential consequences and developing international agreements to safely deploy and monitor geoengineering technologies. If geoengineering were adopted, a combination of techniques would be used depending on cost, regional conditions, and the climate’s response. Different methods may have local or global effects, so regulatory policies need to be agreed upon by the international community. Therefore, many scientists have called for the creation of regulatory agencies to advise the United Nations and lay out plans for how geoengineering methods should be prioritized. Geoengineering could help us reverse climate change in a more controlled manner, buying us time to make our society more sustainable.

        1. Sir….Do you not know they have already been performing GEO Engineering for years. I have personally been documenting this for over a decade. Spraying aluminum oxide into the ionosphere to manipulate the weather cannot be safe for humans or the Planet! They say they are going to save us from Global warming by blocking the sun When in essence they are using this to create the extreme weather. Wake up!

          1. I love laughing at people with at MOST a high school diploma thinking that they’re smarter than Harvard students/professors especially because the author of this article has a PhD🤣🤦‍♂️

  8. humanity is not “driving” climate change, we are accelerating it. I wish people would stop making it dramatic!
    The earth is naturally heating up but we are speeding this process up..
    That is a fact.
    Can you please try to be more objective and not emotionally charge statements and people!

    1. Such truth. We have sped along climate change at a FRIGHTENING pace. Take a look at my website and see what I’m helping bring awareness to. Weather modification/geoengineering and 5g. The have ruined our planet, and destroyed it’s biosphere. All by design 🙁

    2. How is academic Information over dramatic? A lot of scientic Information that is Independent from corporate media like NCBI NIH studies are based on scientific information that is not that common in mainstream media that defends oil corporations. According to statistical information global warming factually increases inflation, cost of living, crimerate, lowers life expectancy, and increases climate refugees. There is a nuance between natural heat and carbon emissions factually worsening the Mental health crisis, crime rate and health problems. War crimes has also increased global warming in the midst of Putin’s invasion of Ukraine according to scientists. Downplaying a problem that harms children and adults is worst than criticizing most corrupt governments doing nothing about global warming. There is no need to pretend that academic journals do not matter because global warming academics is more Independent compared to the mainstream media of the two Party system.

    3. Your statement is misleading at best. I can only assume that you, like many other people struggle with statistics that exhibit exponential growth? We have not just been speeding it up, we’re creating the fastest rise in temperatures the ‘stable earth’ has ever seen. There is no argument about this amongst people who are looking at the data honestly or are not just cheering for a political team. We’re well past this natural warming argument. It died in the 1990s.

      1. You wrote: “we’re creating the fastest rise in temperatures the ‘stable earth’ has ever seen.”
        This is absolutely incorrect.
        This climate had always have natural variations.
        The earth was in what is called a “little ice age” and is escaping it… That’s all!
        “people who are looking at the data honestly”
        Who? People formed in statistics?
        Graphics and datas are NOT telling anything by themselves.
        They need interpretations. This is the work of formed scientists (or clever persons who take time to put the datas in the appropriate context, use their critical mind to study – not just look at – the datas, etc).
        The FACT is: we don’t even have sufficient datas from our History to compare what we are modifying as human beings. The only certainty is about the natural cycle and the little ice ages that have ever exist. Geologists are certain about it. They are not even sure about the nature of the atmosphere at those periodic eras…

        Now, I am not saying that human beings are not destroying the planet. But, to me, the problem is not about the CO2 and all this absurdities (CO2 nourishes plants!)

        To me the problem is that we are destroying the earth by stupid agricultural practices: plowing is killing the soil, for example; cutting down trees is the best way to avoid the water to enter the depth; removing embankments the same…

        And what about biodiversity? What about NON HUMAN BEINGS?!
        Who are we to destroy a planet that we SHARE with many other life forms?!
        Who are we to forget that we are NOTHING without them?!

        Climate change is a distraction to make people look at details when the GLOBAL change is elsewhere…

        About 1990 :

        Have a good day.

    4. How can you say that we, human beings, are speeding a process nobody is really understanding due to a lack of datas?
      Our implication in the heating is absolutely not a fact… as you can’t isolate our actions!
      The most serious scientists are even saying that the CO2 that the humanity reject is nothing behind the CO2 that plants reject.
      And the other particles are not even causing anything important on the climate.
      These are “facts” that scientists say today in medias that are (of course) ignored by the main stream medias and governments wanting to establish new taxes again and again… for everyone, of course, not just industries (whish always manage to be exempted from paying them by doing some fiscal tricks…)
      I agree: it’s very important to be objective and not emotional, because otherwise you validate a false reality and act stupidly …. which is exactly what corrupted govs want all over the planet…

  9. This was a great article, well written and researched. Great information and wasn’t afraid of broaching the subject of collateral damage.
    How many of us are looking up? I don’t believe we do that any more or you’d see it for yourself – it’s happening now 🙂

  10. I became interested in geoengineering when I noticed the sky in Colorado covered in contrails that didn’t dissipate but created a veil of clouds. And it wasn’t every day. Interesting that for a week no conrtrails then I’d notice the high flying jets putting it out there – definitely in a pattern. I’m tracking them now, taking pics and doing research- interesting I contacted my representative and received no reply- it’s definitely happening l, I can see it .

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