Current schemes to minimize the havoc caused by global warming by purposefully manipulating Earth's climate are likely to either be relatively useless or actually make things worse, researchers say in a new study. The dramatic increase in carbon dioxide levels in the atmosphere since the Industrial Revolution is expected to cause rising global sea levels, more-extreme weather and other disruptions to regional and local climates. Carbon dioxide is a greenhouse gas that traps heat, so as levels of the gas rise, the planet overall warms. In addition to efforts to reduce carbon dioxide emissions, some have suggested artificially manipulating the world's climate in a last-ditch effort to prevent catastrophic climate change. These strategies, considered radical in some circles, are known as geoengineering or climate engineering.

Large-scale human engineering of the Earth's climate to prevent catastrophic global warming would not only be ineffective but would have severe unintended side effects and could not be safely stopped, a comparison of five proposed methods has concluded. Science academies around the world as well as some climate activists have called for more research into geoengineering techniques, such as reflecting sunlight from space, adding vast quantities of lime or iron filings to the oceans, pumping deep cold nutrient-rich waters to the surface of oceans and irrigating vast areas of the north African and Australian deserts to grow millions of trees. Each method has been shown to potentially reduce temperature on a planetary scale.

But researchers at the Helmholtz Centre for Ocean Research Kiel, Germany, modelled these five potential methods and concluded that geoengineering could add chaos to complex and not fully understood weather systems. The potential side effects would be potentially disastrous, say the scientists. Ocean upwelling, or the bringing up of deep cold waters, would cool surface water temperatures and reduce sea ice melting, but would unbalance the global heat budget, while adding iron filings or lime would affect the oxygen levels in the oceans. Reflecting the sun's rays into space would alter rainfall patterns and reforesting the deserts could change wind patterns and could even reduce tree growth in other regions.


In addition, say the scientists, two of the five methods considered could not be safely stopped.

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