Fears for geoengineering experiment
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A planned balloon test flight is under fire from environmentalists who fear it is a step towards solar radiation management that could see particles released into the atmosphere to reduce global warming
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Stratospheric Controlled Perturbation Experiment: Following balloon test flight, second experiment would scatter particles to mimic effect of volcanic eruption 

Sun

High altitude balloon

Altitude: 20km

Calcium carbonate: Around 2kg scattered into atmosphere, creating cloud about 1km long

If some solar radiation is successfully deflected away,
it could pave way for larger experiments using substances like sulphur dioxide
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Swedish Space Corporation, Kiruna: Harvard scientists want to test fly high-altitude balloon to see if it can carry equipment for future solar radiation management experiments

SWEDEN
EUROPE
500km 300 miles
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Ash rises 35km into stratosphere

June 15, 1991: Mount Pinatubo erupts, ejecting 5km3 of material

Satellites track ash cloud several times around world
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Sulphurous debris spewed into atmosphere from Pinatubo volcano cools global temperatures by around 0.6°C for 15 months

PHILIPPINES
500km 300 miles
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Sources: Guardian, Scientific American, NASA
Picture: Associated Press
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