CNN is reporting on a way to combat climate change without reducing greenhouse-gas-emissions. Solar shielding has long been hypothesized as a method to limit the amount of heat coming into the Earth’s atmosphere, rather than limiting the amount of heat retained by greenhouse gasses.

Because Solar shielding limits energy input before it ever comes into contact with greenhouse gasses it also provides a way to combat non-anthropogenic global warming. But scientists do warn against tampering with little understood systems.

The idea of the most ambitious systems designed is to dampen sunlight, and the warmth it carries, before it ever reaches the Earth’s atmosphere. They range from a glass reflecting panel at the inner Lagrange point between the Earth and the Sun, to a flock of small “parasols” around the earth, and even to an artificial planetary ring around the Earth made up of passive particles. The costs for such solutions would most likely be in the trillions of US dollars.

Sulphur offers a solution that would be both more affordable and more controversial. Sulphur particles spewed out by volcanoes are largely responsible with the drop in global temperature associated with the years after an outburst. Artificially pumping large amounts of sulfur into the upper atmosphere could potentially lower temperatures to levels last seen in the early years of the 20th century.

But using sulphur is not controversial for nothing. There’s no knowing what such a “sulphur shield” in the upper atmosphere would do to the ozone layer. On top of that it’s possible, even probably, that acid rain would increase in such a scenario, and so might incidence of respiratory illnesses.

No-one is currently advocating deploying any form of solar shield, but scientists warn that if other meassures are not taken it may become necessary. That makes it important to consider and develop the ideas, if only as an “if all else fails” insurance policy.