Combination of carbon emissions and urban hot island effect of concrete and asphalt gives rise to worst-case scenario by objective of 21 st century

Under a dual onslaught of global warming and localised urban heating, some of the worlds cities may be as much as 8C( 14.4 F) warmer by 2100, researchers have warned.

Such a temperature spike would have dire outcomes for the health of city-dwellers, rob companies and industries of able employees, and put pressure on already strained natural resources such as water.

The projection is based on the worst-case scenario assumption that emissions of greenhouse gases continue to rise throughout the 21 st century.

The top one-quarter of most populated cities, in this scenario, could see temperatures rise 7C or more by centurys end, told a study in the publication Nature Climate Change.

For some virtually 5C of the total would be attributed to average global warming.

The rest would be due to the so-called urban heat island effect, which occurs when parks, dams and ponds, which have a cooling consequence, is hereby replaced by concrete and asphalt stimulating cities warmer than their surrounds, the researchers said.

The top 5%[ of cities by population] could see increases in temperatures of about 8C and larger, survey co-author Francisco Estrada of the Institute for Environmental Study in the Netherlands said.

Estrada and a team utilized different projections of average planetary warming, combined with the UHI effect and potential damages, to estimate the future costs of warming on cities.

The median city, right in the midst of the range, stands to lose between 1.4% and 1.7% of GDP per year by 2050 and between 2.3% and 5.6% by 2100, they conclude.

For the worst-off city, loss could reach up to 10.9% of GDP by 2100, wrote the team.

UHI significantly increased city temperatures and economic losses from global warming, they added.

This meant that local actions to reduce UHI such as planting more trees or cooling roofs and pavements could make a big difference in limiting warming and minimising costs.

Cities cover merely about 1% of earths surface but render about 80% of gross world product and account for around 78% of energy consumed worldwide, say the researchers.

They render more than 60% of global carbon dioxide emissions from burning coal, oil and gas for fuel.

The worlds nations agreed in Paris in 2015 to the goal of restriction median global warming to two degrees centigrade over pre-industrial revolution levels by curbing greenhouse gas levels in the Earths atmosphere.

For the latest study researchers use data from the worlds 1,692 largest cities for the period 1950 to 2015.

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