November 14, 2017

expert reaction to research on solar geoengineering and tropical cyclones

A new article, published in Nature Communications, examines impacts of hemispheric solar geoengineering on tropical cyclone frequency.

Dr Peter Irvine, Research Fellow at Harvard University, said:

“This idealized study provides insights into the climate effects of volcanic eruptions which often produce a stratospheric aerosol cloud that is concentrated in one hemisphere or the other. Their results provide support to the observational evidence that volcanic aerosol clouds in the Northern Hemisphere reduce Atlantic tropical cyclone activity, and vice versa for the Southern Hemisphere. This finding could help countries be better prepared for the impacts of the next large volcanic eruption.

“It is obvious from first principles that stratospheric aerosol geoengineering deployed in only one hemisphere would lead to large shifts in Tropical climate patterns. Here they show that deploying only in the Northern Hemisphere would substantially reduce North Atlantic tropical cyclone activity but an earlier study showed that doing so would also lead to a severe drought in the Sahel. They show that a symmetric deployment of stratospheric aerosol geoengineering would not lead to these large shifts in Tropical climate patterns.

“Deploying stratospheric aerosol geoengineering in only one hemisphere is pretty certainly a bad idea and this work helps reinforce that view.”

Prof. John Shepherd FRS, Professorial Research Fellow in Earth System Science at the University of Southampton, said:

“This is a very useful paper by a highly competent team using state-of-the-art modelling and analysis tools. It confirms that solar geoengineering at a global scale could potentially be useful to reduce some of the major impacts of climate change. However, attempting to fine-tune the climate response by using regional forcing is likely to cause unexpected side-effects.

“The effects of geoengineering in one hemisphere or the other are likely to shift tropical weather systems, and cause opposing effects on tropical cyclone (hurricane) activity and drought in the northern hemisphere.

“Even the best current models still have difficulty in accurately simulating important small-scale features such as tropical cyclones and rainfall events, and the computations are expensive, so we still need these results to be replicated by multiple model runs and by different models. Meanwhile it is clear that it is going to take a long time before we can predict the effects of solar geoengineering well enough to be confident that we could design an intervention that was both safe and effective.

“This is not a technique that is ready to use in the near future: reducing CO2 emissions and planning our adaptation to climate change must remain the top priorities for climate policy.”

Dr Hugh Hunt, Reader in Engineering at the University of Cambridge, said:

“This is an excellent and exceptionally timely piece of work.  A very elegant and thorough study using the most advanced models available to show that tropical cyclone activity is significantly affected by stratospheric aerosol injection – but the effects are highly regional.  The work ‘reemphasises the perils of unilateral geoengineering’.

“It is unlikely that climate negotiators at COP23 will actively take this message into account, which is unfortunate given that the COP21 target of stabilising global-mean warming at 1.5 K above pre-industrial levels is probably unachievable without some drastic (geoengineering?) action.  The paper calls for international regulation to control large-scale solar geoengineering deployment – surely just the stuff for COP23 – an opportunity missed?”

* ‘Impacts of hemispheric solar geoengineering on tropical cyclone frequency’ by Anthony C. Jones et al. published in Nature Communications on Tuesday 14 November.

Declared interests

Prof. John Shepherd: No conflicting interests

Dr Hugh Hunt: I have no interests to declare

Dr Peter Irvine: I am part of Prof. David Keith’s group, my post-doc position is funded through the Fund for Innovative Climate and Energy Research: https://keith.seas.harvard.edu/FICER  From that link:
“Grants for research are provided to Harvard University from gifts made by Mr. Bill Gates from his personal funds. The activities of the Fund for Innovative Climate and Energy Research fall outside the scope of activities of the Bill & Melinda Gates Foundation. FICER is not a Foundation project and has no relationship with it.”

I have no financial interests in geoengineering or any other conflicting interests.