Cloud seeding has been seen as a possible method of decreasing the overall surface temperature of the globe. Seeding our planets maritime boundary layer clouds would increase the number of raindrops released from these clouds and reduce the average droplet size, thus increasing their albedo (Rasch et al. 2009). This could result in the cooling of the planet and compensation for some of the negative effects of climate change. The effects of cloud seeding were looked at on a model that represented a globe whose atmospheric CO2 concentrations were twice as high as they are today. Global surface temperature, polar sea ice cover, and the global precipitation rate would experience drastic changes if this cloud seeding strategy were put into action. We would see an overall cooling of the planet, a halt in the rapid shrinking of the polar ice caps, and an overall decrease in the global rate of precipitation.—Ellie Pickrell
Rasch, Philip J., Latham, John, Chen, Jack, 2009. Geoengineering by Cloud Seeding: Influence on Sea Ice and Climate System. Environmental Research Letters, 4.
Philip J. Rasch and the Pacific Northwest National Laboratory conducted an experiment where they examined the effects of cloud seeding on an “Earth” with atmospheric CO2 concentrations that were twice as high as present day values. They used a Community Climate System Model and set up four different geoengineering situations, with a control system that consisted of zero climate engineering. The four cases were 20%, 30%, 40%, and 70% cloud seeding of the areal extent of the ocean surface. They then examined the effects that these four situations had on global surface temperature, polar sea ice, and global precipitation.
The test showing effects of cloud seeding on the Earth’s surface temperature produced promising results. The control group showed an increased surface temperature by 1.8 K compared to the Earth’s current conditions, but the models that included cloud seeding show much more positive results. In the 20% case, the warming is reduced to 0.8 K more than the current day temperatures, which is almost half as much heating if we were to dismiss the idea of cloud seeding. The 70% case actually produced a cooling of 0.4 K less than the current day temperatures, which would actually result in an overcooling of the planet. Based on the results, it is clear that the maximum amount of cloud seeding isn’t necessary, and even the minimum amount of 20% would make a fifty percent difference in the surface temperature.
Next, they compared the results regarding the polar sea ice covers and their reaction to cloud seeding. In this experiment they looked at the effects that cloud seeding would have on the Northern Hemisphere and the Southern Hemisphere separately, as the clouds in the Southern Hemisphere require less seeding than the clouds in the Northern Hemisphere (they are more susceptible to brightening). The control group shows a 20% decrease in the Northern Hemisphere and a 36% decrease in the Southern Hemisphere from the current sea ice levels. In the 40% case the sea ice is 9% smaller than the control group in the Northern Hemisphere, and 8% smaller in the Southern Hemisphere. To really make a difference in the polar ice caps, the Earth requires a 70% cloud seeding strategy, which is almost impossible as it may overcool the Earth. Regardless, in the 70% case the sea ice is restored to within 2% of the present day level.
Finally, they looked at the effect that cloud seeding could have on the global precipitation rate. As the percentage of cloud seeding increases, the global precipitation rate decreases. The control group shows an increase by 0.1 mm of rain, compared to the current day precipitation rate, per day. The 20% case shows an increase by 0.01 mm of rain, while the 70% case shows a decrease by 0.08 mm of rain. These reductions in precipitation occur along the equator between the eastern Pacific and the maritime subcontinent, especially across South America. For all the cases there is, however, an increase in precipitation in the South Pacific convergence zone.
It is important to realize that this study shows how difficult it is to address multiple changes resulting from climate change. If the atmospheric CO2 concentrations were to double, it would be impossible to simultaneously cool the planet, or return sea ice and global precipitation to the present day amounts. —Ellie Pickrell