Can Marine Cloud Brightening Reduce Sea-Surface Temperatures to Moderate Extreme Hurricanes and Typhoons?

Review Article

Austin Environ Sci. 2021; 6(3): 1062.

# Can Marine Cloud Brightening Reduce Sea-Surface Temperatures to Moderate Extreme Hurricanes and Typhoons?

Salter SH*

Institute for Energy Systems, School of Engineering, University of Edinburgh, Scotland

*Corresponding author: SH Salter, Institute for Energy Systems, School of Engineering, University of Edinburgh, Scotland

Received: June 29, 2021; Accepted: July 26, 2021; Published: August 02, 2021

## Abstract

Elevated sea-surface temperatures are a necessary but not sufficient requirement for the formation of hurricanes and typhoons. This paper suggests a way to exploit this. Twomey [1] showed that cloud reflectivity depends on the size-distribution of cloud drops, with a large number of small drops reflecting more than a smaller number of larger ones. Mid-ocean air is cleaner than over land. Latham [2-4] suggested that reflectivity of marine stratocumulus clouds could be increased by releasing a submicron spray of filtered sea water into the bottom of the marine boundary layer. The salt residues left after evaporation would be mixed by turbulence through the full depth of the marine boundary layer and would be ideal cloud condensation nuclei. Those that reached a height where the air had a super-saturation above 100% by enough to get over the peak of the Köhler curve would produce an increased number of cloud drops and so trigger the Twomey effect. The increase in reflection from cloud tops back out to space would cool sea-surface water. We are not trying to increase cloud cover; we just want to make existing cloud tops whiter. The spray could be produced by wind-driven vessels cruising chosen ocean regions. The engineering design of sea-going hardware is well advanced. This paper suggests a way to calculate spray quantities and the number and cost of spray vessels to achieve a hurricane reduction to a more acceptable intensity. It is intended to show the shape of a possible calculation with credible if not exact assumptions. Anyone with better assumptions should be able to follow the process.

Keywords: Hurricane; Typhoon; Cloud-reflectivity; Sea-surface temperature; Twomey effect; Spray vessel

## Introduction

Readers will not need reminding of the damage caused by Atlantic hurricanes in the autumn of 2017 and by Typhoon Haiyan in 2013. So far the results of attempts to control hurricanes [6,7] have been at best inconclusive. This may have been because action was taken after the hurricane had already formed so that energy levels were already very high. If you want to moderate a hurricane tomorrow, you will be far too late. You should have started last November. There were also concerns about legal liability for any events following an attempt at an unsuccessful reduction. A first assumption of this paper is that Governments of countries, which have previously suffered from hurricane damage, could all agree on what sea-surface temperatures would present a lower risk and so be a desirable target. Satellites can now make good measurements of anomalies in sea-surface temperature. The number of spray vessels to be deployed would be chosen with information based on the trajectory of temperature rise. By doing the control continuously rather than over a few days, the enormous power requirements are reduced by about two orders of magnitude.

## What Temperature Reduction Do We Need?

Whitney and Hobgood [8] analyzed the relationship between hurricane intensity defined from wind velocity, and sea- surface temperatures. Figure 1 of this paper is taken from Figure 1 of theirs. The absence of events at the top end of the temperature range is a puzzle. Whatever the reason for the cut off, these data suggest that a reduction of 2 degrees Kelvin would be a useful target for initial engineering feasibility studies.