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Aerosols to protect Earth from global warming will be sprayed into the stratosphere NEXT YEAR

Aerosols to protect Earth from global warming will be sprayed into the stratosphere NEXT YEAR
12 Apr

Harvard researchers are set to test aerosol sprays that could be used to combat climate change.

The controversial technique could one day be used to block incoming solar radiation and cool down Earth to combat the effects of global warming.

The first-of-its-kind experiment could begin as early as next year and will pump small amounts of material into the stratosphere to reflect the sun's rays.

But scientists have previously warned that the results of changing our own climate could be 'catastrophic'.

It will test the feasibility of what scientists are calling 'solar geoengineering' - though the Harvard team say that they will only use water vapour at first.

During testing, the team will analyse a variety of aerosol materials that could be used at scale in future.

But the researchers claim that they will not fire more than 1kg (2.2lbs) of any substance into the stratosphere during testing.

The idea has stirred controversy in the scientific community, even among those who believe it could effectively tackle global warming.

'The idea that you could even think about adjusting the temperature of the planet is terrifying,' Frank Keutsch, one of the Harvard scientists leading the study, told Seeker.

'But the consequences of climate change are also quite terrifying. This is a very serious subject.'

In 2014, researchers warned of what might happen if climate engineering stopped after a few decades for technical or political reasons.

‘For several methods we saw a rapid change in the simulated climate when climate engineering ended,’ said Dr David Keller from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.

For example, if after 50 years the sun's rays were no longer partially blocked, Earth warmed by several degrees within a few decades.

Dr Keller said: ‘This change would be much faster than the current rate of climate change, with potentially even more catastrophic consequences.’

Research last year suggested that pumping the equivalent of 'antacid' tablets into the air could be the answer to climate change.

Experts believe that releasing an aerosol of calcium carbonate into the atmosphere would cool the air, without damaging the ozone layer.

The Paris climate agreement in 2015 set the goal of keeping global temperatures no higher than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above the 'pre-industrial levels'.

Emission reductions will be key to achieving these, but researchers believe that extra efforts can further reduce the risks.

Previous research had focused on ways of limiting the ozone damage by using non-reactive aerosols.

However, the research from last year looked at highly reactive aerosols.

'Instead of trying to minimise the reactivity of the aerosol, we wanted a material that is highly reactive but in a way that would avoid ozone destruction,' said co-author Frank Keutsch.

After examining stratospheric chemistry and ruling out most of the periodic table, the researchers landed on calcite - a constituent of limestone.

They found that this could neutralise emission-based acids in the atmosphere while also reflecting light and cooling the planet.

'Essentially, we ended up with an antacid for the stratosphere,' said Keutsch.

Calcite is one of the most common compounds in the Earth's crust, and only a small amount would be needed for the solar geoengineering.

The researchers are currently testing calcite in the lab conditions designed to mimic the atmosphere.

While it may help to alleviate the problem, the researchers note that this method of solar engineering is not a solution to climate change.

'Geoengineering is like taking painkillers,' said Keutsch.

'When things are really bad, painkillers can help but they don't address the cause of a disease and they may cause more harm than good. We really don't know the effects of geoengineering but that is why we're doing this research.'

The research is published in the Proceedings of the National Academy of Sciences.


Afforestation: This technique would irrigate deserts, such as those in Australia and North Africa, to plant millions of trees that could absorb carbon dioxide.
Drawback: This vegetation would also draw in sunlight that the deserts currently reflect back into space, and so contribute to global warming.

Artificial ocean upwelling: Engineers would use long pipes to pump cold, nutrient-rich water upward to cool ocean-surface waters.
Drawback: If this process ever stopped it could cause oceans to rebalance their heat levels and rapidly change the climate.

Ocean alkalinisation: This involves heaping lime into the ocean to chemically increase the absorption of carbon dioxide.
Drawback: Study suggests it will have of little use in reducing global temperatures.

Ocean iron fertilisation: The method involves dumping iron into the oceans to improve the growth of photosynthetic organisms that can absorb carbon dioxide.
Drawback: Study suggests it will have of little use in reducing global temperatures.

Solar radiation management: This would reduce the amount of sunlight Earth receives, by shooting reflective sulphate-based aerosols into the atmosphere.
Drawback: Carbon dioxide would still build up in the atmosphere.

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