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Want cooler cities? Paint buildings white

Painting roofs white could take the edge of extreme temperature events.
Painting roofs white could take the edge of extreme temperature events.

As meeting the Paris goal of limiting global temperature rise to less than 2°C becomes an increasingly difficult prospect, talk has turned to “highly contentious” geoengineering – impregnating oceans with iron, spraying sulphate aerosols into the atmosphere and even building giant space mirrors to reflect the sun. These solutions, though, are likely to affect climate systems in unpredictable ways, and may make certain countries worse off.

But new research published in Nature Geoscience, has put forward a lower-risk way of shaving up to 2-3°C off extreme temperatures – making the land more reflective by lightening buildings, roads and infrastructure in urban areas; and changing agricultural practices in rural areas.

The research found that changing land surface albedo (the proportion of radiation reflected back into the atmosphere) in North American, Europe and Asia was a “climate engineering” approach that had fewer risks than other solutions, and had already been proven.

While the technique wouldn’t help to reduce global temperatures, it could provide substantial relief on a local and even regional scale during extreme temperature events.

The international research included input from Australia’s ARC Centre of Excellence for Climate Extremes.

The centre’s director professor Andy Pitman said the research proved the effectiveness of strategies like white buildings in “clipping the upper tail of extreme temperatures”.

“Extreme temperatures are where human and natural systems are most vulnerable,” he said.

“Changing the radiative properties of land helps address this issue with fewer side effects.”

In cities this could lead to fewer deaths from extreme temperatures, less pressure on the grid during heatwaves due to cooler indoor temperatures and less need for airconditioning, and less risk of train tracks bending due to heat.

“If you can bring the extreme temperature down a degree or two you reduce the risks,” he told the Thomson Reuters Foundation.

“And that might mean you don’t trigger the brownout – or a human health catastrophe.”

He said strategies like painting buildings white weren’t knew.

“Italians and Greeks worked this out a thousand years ago.”

The research also noted that higher reflectivity roofs were cheaper to implement and easier to install than green roofs, and the reflective measures were superior to enhanced vegetation cover.

However, there are many other benefits to green roofs aside from cooling the environment.

In rural settings, actions included no-till farming, changed crop phenology and timing of practices, bioengineering to increase reflective properties of plants, and greenhouses.

The research also modelled impacts on average temperatures, finding only small changes; and rainfall, with little change except in Asia.

The authors concluded that small increases in surface albedo were worth examining in key areas, such as major cities and agricultural areas, and even though it wouldn’t help reach Paris goals, lessening extreme temperatures could mitigate some of the worst effects of climate change.

“Potentially, the resulting differences could help to keep some regional impacts closer to those associated with a global warming of 1.5°C even under a global warming nearer to 2°C, or partly counteract the impacts of CO2 concentrations overshooting on the way towards temperature stabilisation.”

Lead author Professor Sonia Seneviratne of ETH Zurich said there were multiple considerations to be factored in, and warned that climate engineering was just one amongst many necessary strategies.

“Regional land-based climate engineering can be effective but we need to consider competing demands for land use, for instance for food production, biodiversity, carbon uptake, recreational areas and much more before putting it into effect,” she said.

“We must remember land-based climate engineering is not a silver bullet; it is just one part of a possible climate solution, and it would have no effects on global mean warming or ocean acidification. There are still important moral, economic and practical imperatives to consider that mean mitigation and adaption should still remain at the forefront of our approach to dealing with global warming.”

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