There are numerous issues to be resolved with climate change—rising sea levels, desertification, ocean acidification, mass extinctions, stronger and more frequent natural catastrophes, etc.—so its going to take several solutions to be able to deal with all of them. However, given the extent to which humanity has already polluted the atmosphere for the past few decades, barring any other major advance in science, geoenginneering will be necessary to try to reverse the current trend in pollution. I feel that humanity will have to eventually pick one or both of the following options to try to prevent significant damage and fatalities.
Releasing aerosol sulfates:
According to the Yale Climate Connections, "Aerosols are the primary reason why Earth is still at around 380 parts per million CO2-equivilent (CO2e), rather than the 460 ppm CO2e projected if all the positive forcings were added together.... Aerosols decrease radiative forcing in two ways: through direct aerosol effects as a result of an increased scattering and absorption of incoming solar radiation, and through indirect effects resulting from their ability to serve as cloud condensation nuclei."
At the same time, however, sulfate aerosols are becoming more and more strictly regulated around the world, which seems counterproductive to reducing global warming. The reason for this is that, especially in the lower atmosphere, sulfate pollution causes acid rain (especially compounded by their role as cloud condensation nuclei), which would also cause significant amounts of damage if allowed to run rampant. It's been proposed though, that releasing sulfate particles into the stratosphere (above the clouds) would give us the positive effects of scattering sunlight without causing significant amounts of acid rain. This is one of the same ways that large volcanic eruptions cause cooling.
It has other drawbacks as well though. Sulfate is damaging to the ozone layer, which happens to be contained in the stratosphere. It could be released in the upper stratosphere, but it's altitude will still decay over a period of a few years, causing it to drift through the ozone layer and eventually fall to the ground, likely as acid rain. Additionally, more and more sulfate yields diminishing returns, due to clumping of the particles, but harsher repercussions, so although it can ideally reduce the rate of warming to 10-20% of current levels, this plan alone will not be enough, it only buys time. Some early modelling that there is a sweet spot in terms of how much sulfate to release without severe negative impacts, but scientists describe it as a risky maneuver with potentially unforeseen consequences.
Not all nations would agree to such a plan either, as nations like Russia are predicted to benefit overall from continued global warming. The plan itself though would only cost around a couple billion dollars each year, which is well within the reach of many governments and even individual billionaires, which threatens the possibility of someone doing this as a rogue act without international approval.
The first small scale atmospheric tests are scheduled to take place within a year to test sulfate's effectiveness. It's possible that a similar but safer chemical will be found for this plan, but so far there are not many great candidates, which is why the next option would be preferable, if feasible.
Carbon capture and nuclear power
Carbon capture is currently incredibly expensive and inefficient, usually costing more in CO2 emissions from the electricity is requires than it actually retrieves from the air. Recently, however, its efficiency has been increasing while its cost has been cut by over two-thirds with a new "carbon neutral"method. It essentially captures CO2 from the air and converts it back into fossil fuels, the reverse of the chemical process of burning fossil fuels, and sells these back into the market. If all fossil fuels were generated by this method, they would have a net zero impact on the environment. Even with a net zero impact though, the effects of the current levels of carbon dioxide will continue global warming, so governments could buy fossil fuels themselves and take them out of the economy, for example, by storing them underground again.
Nuclear power, being one of the best sources of green energy out there, can also reduce emissions and power the process of carbon capture. Uranium is approximately 8000 times more energy dense than coal per gram. The US already receives 20% of it's power from 98 nuclear reactors, which are mostly outdated. New safety mechanisms in recent years have significantly decreased the chances of accidents (e.g. "meltdown-proof" molten salt reactors). Even accounting for possible future nuclear disasters, the death rate of coal and oil is drastically higher, due to the inhalation of air pollution. Additionally, as demonstrated by Germany, the world's leading country in renewable energy, wind, solar, and hydro-power cannot sustain the grid due to the fact that there is currently no feasible way to store the energy produced in the day/summer to save it for the night/winter, when energy consumption is highest. Nuclear is, ironically, far more sustainable, as well as easier to implement. It would take over 20,000 square miles of solar panels to power the US alone, compared to around 500 nuclear plants to power the US, or merely 5,300 nuclear plants to meet the global energy consumption level. Hydroelectric has already been implemented where practical, and has little room to expand. Nuclear plants are also cheap to maintain and are already competitive with fossil fuel-based energy sources.
Releasing aerosol sulfates:
According to the Yale Climate Connections, "Aerosols are the primary reason why Earth is still at around 380 parts per million CO2-equivilent (CO2e), rather than the 460 ppm CO2e projected if all the positive forcings were added together.... Aerosols decrease radiative forcing in two ways: through direct aerosol effects as a result of an increased scattering and absorption of incoming solar radiation, and through indirect effects resulting from their ability to serve as cloud condensation nuclei."
At the same time, however, sulfate aerosols are becoming more and more strictly regulated around the world, which seems counterproductive to reducing global warming. The reason for this is that, especially in the lower atmosphere, sulfate pollution causes acid rain (especially compounded by their role as cloud condensation nuclei), which would also cause significant amounts of damage if allowed to run rampant. It's been proposed though, that releasing sulfate particles into the stratosphere (above the clouds) would give us the positive effects of scattering sunlight without causing significant amounts of acid rain. This is one of the same ways that large volcanic eruptions cause cooling.
It has other drawbacks as well though. Sulfate is damaging to the ozone layer, which happens to be contained in the stratosphere. It could be released in the upper stratosphere, but it's altitude will still decay over a period of a few years, causing it to drift through the ozone layer and eventually fall to the ground, likely as acid rain. Additionally, more and more sulfate yields diminishing returns, due to clumping of the particles, but harsher repercussions, so although it can ideally reduce the rate of warming to 10-20% of current levels, this plan alone will not be enough, it only buys time. Some early modelling that there is a sweet spot in terms of how much sulfate to release without severe negative impacts, but scientists describe it as a risky maneuver with potentially unforeseen consequences.
Not all nations would agree to such a plan either, as nations like Russia are predicted to benefit overall from continued global warming. The plan itself though would only cost around a couple billion dollars each year, which is well within the reach of many governments and even individual billionaires, which threatens the possibility of someone doing this as a rogue act without international approval.
The first small scale atmospheric tests are scheduled to take place within a year to test sulfate's effectiveness. It's possible that a similar but safer chemical will be found for this plan, but so far there are not many great candidates, which is why the next option would be preferable, if feasible.
Carbon capture and nuclear power
Carbon capture is currently incredibly expensive and inefficient, usually costing more in CO2 emissions from the electricity is requires than it actually retrieves from the air. Recently, however, its efficiency has been increasing while its cost has been cut by over two-thirds with a new "carbon neutral"method. It essentially captures CO2 from the air and converts it back into fossil fuels, the reverse of the chemical process of burning fossil fuels, and sells these back into the market. If all fossil fuels were generated by this method, they would have a net zero impact on the environment. Even with a net zero impact though, the effects of the current levels of carbon dioxide will continue global warming, so governments could buy fossil fuels themselves and take them out of the economy, for example, by storing them underground again.
Nuclear power, being one of the best sources of green energy out there, can also reduce emissions and power the process of carbon capture. Uranium is approximately 8000 times more energy dense than coal per gram. The US already receives 20% of it's power from 98 nuclear reactors, which are mostly outdated. New safety mechanisms in recent years have significantly decreased the chances of accidents (e.g. "meltdown-proof" molten salt reactors). Even accounting for possible future nuclear disasters, the death rate of coal and oil is drastically higher, due to the inhalation of air pollution. Additionally, as demonstrated by Germany, the world's leading country in renewable energy, wind, solar, and hydro-power cannot sustain the grid due to the fact that there is currently no feasible way to store the energy produced in the day/summer to save it for the night/winter, when energy consumption is highest. Nuclear is, ironically, far more sustainable, as well as easier to implement. It would take over 20,000 square miles of solar panels to power the US alone, compared to around 500 nuclear plants to power the US, or merely 5,300 nuclear plants to meet the global energy consumption level. Hydroelectric has already been implemented where practical, and has little room to expand. Nuclear plants are also cheap to maintain and are already competitive with fossil fuel-based energy sources.
Unfortunately, this plan would require significant worldwide cooperation and a large shift in public opinion toward nuclear power. Many people are suspicious of nuclear power: 54% of Americans in a 2016 Gallup poll indicated that they opposed the use of nuclear power plants in the US. Even environmentalists are torn on the issue, often supporting policies to shutdown old reactors instead of replacing/renovating them. Based on this, I don't think that the world will be able to come to an agreement on how to halt climate change before harming millions more people in the coming decades. However, we can start taking the first steps. In recent years, public opinion has finally shifted in favor of a carbon tax, which would incentivize companies to reduce their emissions and pursue other sources of energy (i.e. nuclear). Any action now will help to reduce climate change's consequences on future generations.
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