Studies into Marine Cloud Brightening (MCB), discussing the Important Cloud Physics Processes and how MCB could be used to Prevent Coral Bleaching, Ameliorate SSTs and Hurricane Intensity, and Pause Polar Arctic Sea Ice Loss

This study presents results from both global climate model and high resolution cloud simulations as relates to Marine Cloud Brightening (MCB). MCB is the term applied to the increase in brightness / albedo of maritime stratocumulus clouds by injection of sea water droplets. Model results will demonstrate that at low and medium concentrations of Cloud Condensation Nuclei (CCN), the albedo of the clouds increases. Results from a Large Eddy Model describes how the cloud structure changes with increasing CCN number. [1], [2], [3]

As well as reducing global temperatures, Marine Cloud Brightening can effect regional climatologies.

Hurricane Amelioration

A major feature of MCB is the potential to cool ocean surface waters in regions of hurricane genesis and early development. This would be achieved by seeding, with copious quantities of seawater cloud condensation nuclei (CCN), low-level maritime stratocumulus clouds covering these regions or those at the source of incoming currents. Higher cloud droplet density would increase these clouds' reflectivity to incoming sunlight, and possibly their longevity. This approach is therefore a more localised application of the Marine Cloud Brightening (MCB) geoengineering technique promoting global cooling. By utilising a climate ocean/atmosphere coupled model, HadGEM1, we demonstrate that – subject to the satisfactory resolution of defined but unresolved issues – judicious seeding of maritime stratocumulus clouds might significantly reduce sea surface temperatures (SSTs) in regions where hurricanes develop. Thus artificial seeding may reduce hurricane intensity; but still to be determined how the magnitude of this effect could be controlled is. [4]

Coral Bleaching

Increases in coral bleaching events over the last few decades have been largely caused by rising sea surface temperatures (SST), and continued warming is expected to cause even greater increases through this century. The same Global Climate Model will examine the potential of Marine Cloud Brightening to cool oceanic surface waters in three coral reef provinces. Our simulations indicate with doubled CO2 conditions, the substantial increases in coral bleaching conditions from current values in three reef regions (Caribbean, French Polynesia, and the Great Barrier Reef) were eliminated when MCB was applied, which reduced the SSTs at these sites approximately back to their original values. [5]

Meridional Heat Flux

Our results show how regional application of MCB can affect the Planetary Meridional Heat flux from the Equator to the Pole. The atmospheric temperature increases as a consequence Carbon Dioxide and other Green House gases concentration rises. Consequently, by reflecting solar radiation in the subtropical regions, there is a reduction in poleward heat transfer, which has direct impact on the current rapid melt of the Arctic Polar Ice Fields. Climate models (as shown in IPPC AR5 report) are of insufficient resolution to replicate the current increase in Poleward Heat Flux. A warming atmosphere contains more water vapour. This feedback effect, ignored in AR5, produces a larger forcing than the original Carbon Dioxide effect. This presentation will demonstrate the mechanism by which the poles are cooled; as a direct consequence of reducing the incoming shortwave radiation in the sub-tropical regions, [6]

References

[1] Latham et al. (2012) Marine cloud brightening, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 370, pp.4217-4262. doi: 10.1098/rsta.2012.0086

[2] Andrejczuk M; Grabowski WW; Gadian A; Burton R (2012) Limited-are a modelling of stratocumulus over South-Eastern Pacific, Atmospheric Chemistry and Physics, 12, pp.3511-3526. doi: 10.5194/acp-12-3511-2012

[3] Andrejczuk, M., Gadian, A., Blyth, A., (2014) Numerical simulations of stratocumulus cloud response to aerosol perturbation, Atmospheric Research (2014), doi: 10.1016/j.atmosres.2014.01.006

[4] Latham J; Parkes B; Gadian A; Salter S (2012) Weakening of hurricanes via marine cloud brightening (MCB), Atmospheric Science Letters, 13, pp.231-237. doi: 10.1002/asl.402

[5] Latham J; Kleypas J; Hauser R; Parkes B; Gadian A (2013) Can marine cloud brightening reduce coral bleaching?, Atmospheric Science Letters, 14, pp.214-219. doi: 10.1002/asl2.442

[6] Parkes B; Gadian A; Latham J (2012) The effects of Marine Cloud Brightening on Seasonal Polar Temperatures and the Meridional Heat Flux., ISRN Geophysics, 2012, . doi: 10.5402/2012/142872