2. I don’t think this is right, for reasons discussed in this Nature paper. Firstly, solar geoengineering could be used to slow the rate of warming even if it is deployed temporarily. You could deploy it over e.g. a fifty year period and thereby delay the point at which we reach peak warming, and then taper it out gradually. Secondly, as you say, an exception is if CO2 emissions stay above zero. Solar geoengineering could in principle buy us time to abate emissions and to take CO2 out of the atmosphere in which case it would not have to be deployed for the full lifetime of CO2 in the atmosphere. In this case, solar geo would slow the rate of warming and reduce peak warming.
Thirdly, I don’t see why solar geoengineering would ever be stopped suddenly once we started. The reasons for this are discussed in the Parker and Irvine piece on solar geoengineering. All countries would have a reason to prevent it from stopping suddenly and would have the means to do so given how cheap it is. A catastrophe causing termination would have to be extraordinarily specific.
3. To clarify, is your point here that we should focus on mitigation because then we’ll be left with some spare oil come a later catastrophe?
2. My assumptions were that geoengineering might reduce society’s drive for mitigation (the switch to clean energy), and that it would be used to halt the temperature increase.
In the linked paper (Keith & Macmartin 2015) their proposal [actually they use the word “scenario”—I don’t think they are going so far as to endorse it as a plan] is a bit different. They propose to use *half* as much aerosols as would be required to halt global warming (this is a bit tricky to get right, e.g. the radiative forcing of aerosols has much greater uncertainty than the forcing of CO2, so their proposal includes feedback to modify the injections as decades pass and observations are gathered about the effect of the aerosols). The paper says “We do not claim that this scenario is optimal. Rather we claim that good-quality policy-motivated scientific analysis requires an explicit scenario, and that this scenario is less obviously suboptimal than some scenarios employed in the literature.” They point out that the harms of global warming increase superlinearly with temperature change, so I think they are saying that avoiding half the warming, or at least slowing global warming by half, is a reasonable compromise that avoids the worst harms without turning global warming into a total non-issue.
“Temporary deployment does not reduce long-term climate change. Warming in 2300, for example, is almost completely determined by cumulative carbon emissions and is unaffected by SRM that ends in 2200. Some commentators conclude that such temporary SRM offers no benefits, suggesting that it must be maintained forever.” The paper counters that many climate change impacts depend on the rate of change—that if warming is slowed down, it is less harmful even if the total warming over 200 years is left the same. So I think the proposal here is to taper off the aerosol injections in such a manner that, in the worst case, we get the same warming over 200 years rather than 100.
They note that “It is clear that this scenario does not directly address thresholds that are a function only of the magnitude of the change rather than the rate, although it does delay reaching these thresholds, giving more time both to learn about the system and develop alternate strategies.” The total amount of warming in their scenario *would* be decreased if we invent and deploy a technology that can remove CO2 from the air permanently (such technologies are very far from economical today). However, we can’t guarantee we will invent an economical technology to do this. If we don’t, Greenland may still melt under their scenario, but later than it would have otherwise (“in Fig. 1, the time to reach a temperature rise of 2 °C above pre-industrial increases from 2055 to 2068, while the time to reach a 2.5 °C rise increases by 32 years.”).
Regarding stoppage of geoengineering due to catastrophe, they say, “While not discounting the possibility of social collapse, we note that humanity has operated technologies such as trans-oceanic communication links and electric power grids for more than a century in spite of horrific wars. Moreover, in considering the implications of a possible social collapse on the public policy of SRM [Solar Radiation Management], one must set the risks of termination against the (likely) greater human suffering that would arise directly from the collapse itself.” So, if there’s a global catastrophe, a sudden increase in global warming seems like a minor footnote in comparison.
I remain concerned that geoengineering is a distraction that could reduce the pressure to reduce CO2 emissions, but if geoengineering were to become a popular political position, I agree that Keith & Macmartin’s proposal seems better than the “default” geoengineering proposal that people (including me) naively think of, i.e. to simply stop global warming regardless of CO2 emissions.
2. I don’t think this is right, for reasons discussed in this Nature paper. Firstly, solar geoengineering could be used to slow the rate of warming even if it is deployed temporarily. You could deploy it over e.g. a fifty year period and thereby delay the point at which we reach peak warming, and then taper it out gradually. Secondly, as you say, an exception is if CO2 emissions stay above zero. Solar geoengineering could in principle buy us time to abate emissions and to take CO2 out of the atmosphere in which case it would not have to be deployed for the full lifetime of CO2 in the atmosphere. In this case, solar geo would slow the rate of warming and reduce peak warming.
Thirdly, I don’t see why solar geoengineering would ever be stopped suddenly once we started. The reasons for this are discussed in the Parker and Irvine piece on solar geoengineering. All countries would have a reason to prevent it from stopping suddenly and would have the means to do so given how cheap it is. A catastrophe causing termination would have to be extraordinarily specific.
3. To clarify, is your point here that we should focus on mitigation because then we’ll be left with some spare oil come a later catastrophe?
2. My assumptions were that geoengineering might reduce society’s drive for mitigation (the switch to clean energy), and that it would be used to halt the temperature increase.
In the linked paper (Keith & Macmartin 2015) their proposal [actually they use the word “scenario”—I don’t think they are going so far as to endorse it as a plan] is a bit different. They propose to use *half* as much aerosols as would be required to halt global warming (this is a bit tricky to get right, e.g. the radiative forcing of aerosols has much greater uncertainty than the forcing of CO2, so their proposal includes feedback to modify the injections as decades pass and observations are gathered about the effect of the aerosols). The paper says “We do not claim that this scenario is optimal. Rather we claim that good-quality policy-motivated scientific analysis requires an explicit scenario, and that this scenario is less obviously suboptimal than some scenarios employed in the literature.” They point out that the harms of global warming increase superlinearly with temperature change, so I think they are saying that avoiding half the warming, or at least slowing global warming by half, is a reasonable compromise that avoids the worst harms without turning global warming into a total non-issue.
“Temporary deployment does not reduce long-term climate change. Warming in 2300, for example, is almost completely determined by cumulative carbon emissions and is unaffected by SRM that ends in 2200. Some commentators conclude that such temporary SRM offers no benefits, suggesting that it must be maintained forever.” The paper counters that many climate change impacts depend on the rate of change—that if warming is slowed down, it is less harmful even if the total warming over 200 years is left the same. So I think the proposal here is to taper off the aerosol injections in such a manner that, in the worst case, we get the same warming over 200 years rather than 100.
They note that “It is clear that this scenario does not directly address thresholds that are a function only of the magnitude of the change rather than the rate, although it does delay reaching these thresholds, giving more time both to learn about the system and develop alternate strategies.” The total amount of warming in their scenario *would* be decreased if we invent and deploy a technology that can remove CO2 from the air permanently (such technologies are very far from economical today). However, we can’t guarantee we will invent an economical technology to do this. If we don’t, Greenland may still melt under their scenario, but later than it would have otherwise (“in Fig. 1, the time to reach a temperature rise of 2 °C above pre-industrial increases from 2055 to 2068, while the time to reach a 2.5 °C rise increases by 32 years.”).
Regarding stoppage of geoengineering due to catastrophe, they say, “While not discounting the possibility of social collapse, we note that humanity has operated technologies such as trans-oceanic communication links and electric power grids for more than a century in spite of horrific wars. Moreover, in considering the implications of a possible social collapse on the public policy of SRM [Solar Radiation Management], one must set the risks of termination against the (likely) greater human suffering that would arise directly from the collapse itself.” So, if there’s a global catastrophe, a sudden increase in global warming seems like a minor footnote in comparison.
I remain concerned that geoengineering is a distraction that could reduce the pressure to reduce CO2 emissions, but if geoengineering were to become a popular political position, I agree that Keith & Macmartin’s proposal seems better than the “default” geoengineering proposal that people (including me) naively think of, i.e. to simply stop global warming regardless of CO2 emissions.
3. Yes.