India: West Bengal's climate change conundrum: Why Kolkata is more heat-stressed than other megacities

Why are Kolkata’s temperatures rising? – The Urban Heat Island Effect in addition to greenhouse gases

Warming by greenhouse gases is a global phenomenon and, to that extent, contributes to the city’s rising temperature. Yet, there is a second major reason afflicting cities worldwide called the “urban heat island effect”.

The heat island effect can cause temperatures in urban areas to be several degrees higher than the countryside due to high population densities, heat from vehicular exhaust and the use of ACs, dark roads that absorb solar radiation, tall buildings that block wind flow and the lack of sufficient open green spaces.

This effect can be powerful enough at the scale of a city, or sections of it, to swamp temperature rise because of greenhouse gases. However, this effect being localised to city scales only affects the microclimate of the city and has little effect on the global average temperature (most of the Earth’s surface is covered by water or is sparsely populated).

In what is a cause for immense alarm for the city, recent research led by Tom Matthews published in the journal PNAS found that humid heat waves of the devastating intensity of those in 2015 may strike Kolkata on an annual basis for a global average temperature rise of “as little as” 1.5C. These temperatures will be met in about 20 years at the current rate of warming.

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