Solar Radiation Management*
Solar Radiation Management (SRM) is one of two methods falling under the descriptive title of Geoengineering which attempt to combat global warming independently of reducing greenhouse gas emissions from human activities.[1] The first is Carbon Dioxide Removal (CDR).
The second, SRM, aims to counter global warming by reflecting some sunlight back into space, reducing the amount of heat reaching the Earth’s surface.
Solar radiation management with sulphate aerosols
The most commonly discussed method of SRM is the release of sulphate aerosols (sulphur-containing particles suspended in the air) high into the atmosphere to a region called the stratosphere.
The sulphate aerosols would make the stratosphere more reflective, scattering sunlight away from Earth.
This happens occasionally by natural means: when a volcanic eruption releases a large amount of sulphates into the stratosphere, a cooling effect is observed for a few years. Injections of sulphate aerosols into the stratosphere would mimic this process and could induce cooling.
Techniques for getting sulphate aerosols to the upper atmosphere include weather balloons, high altitude planes, or long tubes supported by balloons connected to a sulphate source. The latter strategy appears to be the most technologically and financially feasible method of SRM. The major benefit of reflecting sunlight away from Earth is that it would operate quickly to reduce surface temperatures.
However, SRM would not reverse the underlying cause of global warming: growing emissions of greenhouse gases, and doing the former without attempting to remedy the latter has been compared to the habits of “compulsive eaters who count on frequent liposuction rather than maintaining strict diets to keep their body fat in check and stay healthy”.[2]
Also, other emissions-associated impacts like ocean acidification would remain. Since greenhouse gases from human activities tend to accumulate in the atmosphere, SRM options would have to be continued indefinitely to have a long-term effect. If they failed or were stopped, temperatures would increase within a few years. On the other hand, the quick reversal of temperature once SRM is stopped could act as a failsafe if undesired consequences develop.
Other techniques
Other SRM techniques, largely untested and carrying high levels of
uncertainty and risk include:
But the bottom line is this:
* Source for graphic: Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP), which reviewed a wide range of proposed geoengineering techniques, marine and otherwise...
[1] This is an edited summary of a paper on Geoengineering which may be found at https://www.chiefscientist.gov.au/wp-content/uploads/47019_Chief-Scientist-_OccassionalPaperSeries_lores.pdf It forms part of the Australian Chief Scientist’s Occasional Paper Series and is Issue 1, April 2012.
For other papers on this topic, see the article "Can removing carbon dioxide from the air save us from climate catastrophe?" at https://blogs.ei.columbia.edu/2018/11/27/carbon-dioxide-removal-climate-change/ and, as if in response, the article by Professor Raghu Murtugugge, "We must remove carbon from the atmosphere to limit climate change: here's how we can do it", at https://www.newsweek.com/we-must-remove-carbon-atmosphere-limit-climate-change-1206971
[2] Not part of the Chief Scientist's paper. This is drawn from the Huffington Post, April 6 (2017?), quoted in a course paper by Associate Professor Michael Box (UNSW, retired), Geoengineering: Messing with the Climate to Combat our Current Mess, WEA course, 16 August 2019 at [7.1].
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uncertainty and risk include:
- Increasing earth surface reflectivity – painting urban structures (e.g. roofs) white, cultivating highly reflective plants or placing reflective materials in deserts or on the ocean.
- Space mirrors – reducing the amount of sunlight that reaches the earth by putting reflective materials in space.
- Cloud whitening – increasing the reflectivity and amount of clouds - Brightening marine clouds by spraying fine seawater into low lying stratocumulus clouds to increase their reflectivity and reduce surface temperatures.
But the bottom line is this:
- viewing the problem from a time perspective in 2019, humanity has only 10 years to have large-scale carbon dioxide reduction schemes up and running.
- these schemes would need to be making a significant dent in carbon dioxide levels, as by that point CO2 emissions will likely have reached the limit required to keep global warming to 1.5 degrees Celsius.
- but, here's the rub - "if emissions are not going to be falling globally, is (all this) even worth doing?"
* Source for graphic: Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP), which reviewed a wide range of proposed geoengineering techniques, marine and otherwise...
[1] This is an edited summary of a paper on Geoengineering which may be found at https://www.chiefscientist.gov.au/wp-content/uploads/47019_Chief-Scientist-_OccassionalPaperSeries_lores.pdf It forms part of the Australian Chief Scientist’s Occasional Paper Series and is Issue 1, April 2012.
For other papers on this topic, see the article "Can removing carbon dioxide from the air save us from climate catastrophe?" at https://blogs.ei.columbia.edu/2018/11/27/carbon-dioxide-removal-climate-change/ and, as if in response, the article by Professor Raghu Murtugugge, "We must remove carbon from the atmosphere to limit climate change: here's how we can do it", at https://www.newsweek.com/we-must-remove-carbon-atmosphere-limit-climate-change-1206971
[2] Not part of the Chief Scientist's paper. This is drawn from the Huffington Post, April 6 (2017?), quoted in a course paper by Associate Professor Michael Box (UNSW, retired), Geoengineering: Messing with the Climate to Combat our Current Mess, WEA course, 16 August 2019 at [7.1].
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