One of the methods proposed to cool the planet involves building lots of large floating spray pump systems that would use wind or wave energy to spray water into the atmosphere. The purpose of the water would be to create more white clouds that would reflect away more sunlight and thereby cool the planet. Ken Caldeira and associates find that the ocean spray approach would increase the amount of precipitation on land.
Palo Alto, CA— One proposed emergency fix to halt global warming is to seed clouds over the ocean to make them more reflective, reducing the solar radiation absorbed by the Earth. But the scheme could also change global rainfall patterns, raising concerns of water shortages on land. A new study by the Carnegie Institution, in collaboration with the Indian Institute of Science, suggests that altered atmospheric circulation under the scheme in fact could increase monsoonal rains and cause the continents to become wetter, not drier, on average.
Whitening clouds over the ocean to reflect sunlight is one of several geoengineering schemes proposed to counter global warming. The whitening would be accomplished by reducing the size of the water droplets making up the clouds. "Rain clouds, which have big droplets, tend to be grey and absorb sunlight, whereas clouds with smaller droplets tend to be white and fluffy and reflect more sunlight to space," says co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology. "In practice this could be done by shooting a fine spray of seawater high into the air, where the tiny salt particles would create condensation nucleii to form small cloud droplets."
Cheaper ways to cool the planet exist. Silicon dioxide sprayed into the atmosphere might be the cheapest. The size of the fleet of automated water spraying ships strikes me as a lot more expensive. But increased precipitation might pay back the costs via higher crop yields and more water for cities.
Climate engineering without the continental drying.
To test the climate consequences of doing this, Caldeira and his coauthors* used a computer simulation of the global climate system in which atmospheric carbon dioxide concentrations were set at approximately twice that of present day. Cloud droplets over the oceans in the model were reduced in size to make the clouds more reflective. Clouds over land were unaltered. As expected, the whitened clouds reflected more solar radiation and offset the warming effect of the high carbon dioxide levels.
What surprised the researchers, however, was that the model showed that the oceanic clouds caused the land surface to become cooler and wetter on average. In previous climate simulations diminishing solar radiation by geoengineering had reduced precipitation on land. "The drying of the continents has been a major concern with regard to geoengineering," says Caldeira. But in the model the runoff from the continents increased by 7.5% globally, with the effect being strongest in the tropics.
I would guess that stationing the spray ships upwind of continents would deliver the most precipitation onto land. Especially dry coastal areas such as most of the US west coast might benefit from increased rains.
|Share |||Randall Parker, 2010 June 29 11:21 PM Climate Engineering|