Hi All This is a very interesting result and an important warning about the dangers of 1700 parts per million CO2. It might be possible if difficult to selectively breed more intelligent politicians in the next a hundred years but we would need to know what to do with rejects.
I am not quite so worried about scattered stratocumulus clouds because this indicates a longer life for condensation nuclei. We want a low dose over a wide area and to avoid high local concentrations that we would get from a moving point source. The graphs below of the Twomey effect (via Schwartz and Slingo) show how reflectivity changes as a function of nuclei concentration for different different cloud thicknesses and water contents. [cid:[email protected]] Start on any red or blue curve near the left of the graph. Move to the right along a thick black line to increase nuclei concentration and then upwards to get back to the curve you chose. Then repeat moving twice as far in the nuclei per cm3 direction each time to get successive doublings of nuclei concentration. Each doubling gives almost the same black step increase in reflectivity except for the very thinnest clouds. Cloud thickness and water content are less important than nuclei concentration. Breathe safely Stephen From: [email protected] <[email protected]> On Behalf Of Andrew Lockley Sent: 17 November 2020 19:38 To: geoengineering <[email protected]> Subject: [geo] Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover This email was sent to you by someone outside of the University. You should only click on links or attachments if you are certain that the email is genuine and the content is safe. https://www.pnas.org/content/early/2020/11/10/2003730117.short Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover View ORCID ProfileTapio Schneider, View ORCID ProfileColleen M. Kaul, and Kyle G. Pressel PNAS first published November 16, 2020; https://doi.org/10.1073/pnas.2003730117 Add to Cart ($10) Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved October 7, 2020 (received for review February 27, 2020) Article Figures & SI Info & Metrics PDF Significance Solar geoengineering that manipulates the amount of sunlight Earth absorbs is increasingly discussed as an option to counter global warming. However, we demonstrate that solar geoengineering is not a fail-safe option to prevent global warming because it does not mitigate risks to the climate system that arise from direct effects of greenhouse gases on cloud cover. High-resolution simulations of stratocumulus clouds show that clouds thin as greenhouse gases build up, even when warming is modest. In a scenario of solar geoengineering that is sustained for more than a century, this can eventually lead to breakup of the clouds, triggering strong (5°C), and possibly difficult to reverse, global warming, despite the solar geoengineering. Abstract Discussions of countering global warming with solar geoengineering assume that warming owing to rising greenhouse-gas concentrations can be compensated by artificially reducing the amount of sunlight Earth absorbs. However, solar geoengineering may not be fail-safe to prevent global warming because CO2 can directly affect cloud cover: It reduces cloud cover by modulating the longwave radiative cooling within the atmosphere. This effect is not mitigated by solar geoengineering. Here, we use idealized high-resolution simulations of clouds to show that, even under a sustained solar geoengineering scenario with initially only modest warming, subtropical stratocumulus clouds gradually thin and may eventually break up into scattered cumulus clouds, at concentrations exceeding 1,700 parts per million (ppm). Because stratocumulus clouds cover large swaths of subtropical oceans and cool Earth by reflecting incident sunlight, their loss would trigger strong (about 5 K) global warming. Thus, the results highlight that, at least in this extreme and idealized scenario, solar geoengineering may not suffice to counter greenhouse-gas-driven global warming. global warminggeoengineeringcloud feedback -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-04C%2BAn%3DPFaR%3DSOehEH012HcF1HzVjd4sJEhsW%3Degx9ZKQ%40mail.gmail.com<https://groups.google.com/d/msgid/geoengineering/CAJ3C-04C%2BAn%3DPFaR%3DSOehEH012HcF1HzVjd4sJEhsW%3Degx9ZKQ%40mail.gmail.com?utm_medium=email&utm_source=footer>. The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/PR3PR05MB7354C130846C977D7F2315F8A7E20%40PR3PR05MB7354.eurprd05.prod.outlook.com.
