Climate engineering could lead to less rain

Among political procrastinators of a technocratic bent, the favoured solution to climate change is geoengineering. For example, artificially reducing the amount of sunlight reaching Earth’s surface by mimicking the effects of volcanos which release large quantities of sulphur dioxide into the atmosphere. The thinking is that, if we fail to radically reduce atmospheric carbon dioxide emissions, geoengineering may be the only course of action left open to us.

Environmentalists tend to oppose geoengineering on the grounds that messing with something as big and complex as a planet is fraught with unforeseen consequences. Such fears have so far been based largely on political ideology and gut instinct, but scientific studies are beginning to show what could happen if we engineer the climate on a planetary scale.

The latest research shows that geoengineering could result in disruption to global and regional rainfall patterns, with a reduction of up to 15% of preindustrial precipitation levels in North America and northern Eurasia. The modelling study by Max-Planck meteorologist Hauke Schmidt and his colleagues reveals that global rainfall could be reduced by about five percent on average. This is based on a quadrupling of atmospheric carbon dioxide over preindustrial levels, which is at the upper end of what is considered possible, based on current trends.

Even a couple of percent reduction in global rainfall would have very serious consequences in certain parts of the world, as it would have major impacts on the water cycle on which agriculture depends. Given the seriousness of the problem, the scientists are clear in their conclusion…

“Climate engineering cannot be seen as a substitute for a policy pathway of mitigating climate change through the reduction of greenhouse gas emissions.”

An important point to note is that with geoengineering we cannot reproduce the preindustrial environment; climate is more than temperature alone. Says Schmidt…

“The impacts of these changes are yet to be addressed, but the main message is that the climate produced by geoengineering is different to any earlier climate even if the global mean temperature of an earlier climate might be reproduced.”

The authors stress that their study is not intended to be a realistic simulation of any future geoengineering approach. For one thing there are too many undefined variables to allow for a realistic model the output of which could be used as a basis for policy development. But what the study does do is identify and compare the basic responses of the Earth system to climate engineering. And it doesn’t look good for the would-be geoengineers.

Further reading

Schmidt et al., “Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO2: climate responses simulated by four earth system models”, Earth System Dynamics 3, 63–78 (2012)