Far from offering a simple fix, science-fiction solutions to global warming may in fact make the problem worse, according to a recent probe of "geo-engineering" options. Once mocked as unscientific, geo-engineering proposals are gaining traction as carbon emissions soar, placing earth on track to warm maybe four degrees Celsius by 2100. Ideas, mainly experimental or untested, include building mirrors in space to reflect the sun's rays or growing plankton to boost absorption of heat-trapping carbon dioxide. The goal is to buy time to wean the global economy off the cheap, dirty energy sources driving man-made climate change. On current emissions trends, these technologies stand little chance of rolling back warming to the UN-targeted two degrees and may well make matters worse, according to the study. "Climate engineering alone is not a good solution to prevent climate change," said David Keller of the Helmholtz Centre for Ocean Research in Germany, who co-authored the paper. Reporting in the journal Nature Communications , the team devised a computer model to project the impact of five geo-engineering proposals under a scenario of continuing high carbon emissions. The five schemes entail: planting large forests to absorb carbon dioxide from the atmosphere and store it; fertilising the oceans with iron to stimulate the growth of plankton, which would absorb more carbon dioxide from the sea surface through photosynthesis; using long pipes to pump deep, cold, nutrient-rich water to the surface to fertilise plankton; "alkalising" the ocean with limestone to cause a chemical reaction to absorb more carbon dioxide from the atmosphere; and using solar radiation management - placing reflective particles in the atmosphere or mirrors in space to reflect the sun's rays. Even with the technologies combined and applied to the widest extent possible, these options would not prevent mean surface temperatures from rising beyond the two degrees target if carbon dioxide emissions continue as they were, the simulation found. The side effects "could be as bad as the climate change effects that they are trying to prevent", Keller warned. The study found that solar radiation management was the only method with the potential to swiftly reduce warming, but it also had some of the largest potential side effects, such as changing rain patterns.