Warning signals from IPCC report for Kolkata city
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Climate change closer home - IPCC warning on Kolkata
- The story: Kolkata and its surroundings have warmed up especially and worse is in store, the Intergovernmental Panel on Climate Change (IPCC) report has warned. The metro may experience a 4.5 degree Celsius rise in annual mean temperature in 2081-2100 compared to the pre-industrial period (1850-1900) under the worst possible greenhouse gas emission scenario, according to the report released August 8, 2021.
- Details: Kolkata recorded the highest rise in surface air temperature within the studied cities and regions across the world in 1950-2018. The pre-industrial period (1850-1900) is considered a benchmark; it was during this time that industrialisation was intiated and human-induced emissions started to increase.
- The report predicted that while total rainfall in the city and adjoining areas may increase marginally, short-duration extreme rainfall events would increase substantially.
- The sea level close to Sundarbans at the southern fringe of Kolkata, at the lap of Bay of Bengal, may rise about 60 centimetres during end of the century. The trend is likely to enhance the intensity and duration of flooding in the city during high tides.
- Global highest: The warming in the city increased 2.6°C, followed by Teheran (2.3°C) and Moscow (1°C) during this time. Urbanisation contributed to a rise in the city’s temperature, with more than 80 per cent warming being generated within the city itself. Urban centres and cities were warmer than the surrounding rural areas due to the urban heat island effect.
- Urban heat island effect: This effect arises from several factors, including reduced ventilation and heat being trapped as tall buildings are closely packed in a small area; heat generated from human activities; heat-absorbing properties of concrete and other urban building materials; and limited amount of vegetation.
- Kolkata is a highly unplanned city, with high concretisation and extremely limited vegetation
- Kolkata’s greenery quotient is also one of the lowest in India
- The data analysis under various greenhouse emission scenarios showed that the annual mean temperature may increase 4.5°C by end of the century compared to the pre-industrial period under business-as-usual emission scenario Representative Concentration Pathway (RCP) 8.5.
- RCP 8.5 accounts for 3-4°C global average temperature rise compared to compared to pre-industrialisation times.
- Even under the best possible emission scenario RCP 2.6, which aims to keep temperature rise under 2°C, the rise will be 1.6°C during 2080-2100. The rise will be 2.4°C under the likely scenario of RCP 4.5, which acknowledges 2°C global temperature rise.
- Recent degradation: This rise in temperature has been a recent phenomenon, as about 80 per cent rise in the city is slated to have happened after 2014. During 2021-2040, the rise would be around 0.9°C compared to pre-industrialisation time; it will be 1.4-1.9°C during 2041-60.
- Super cyclones, sharp sea level rise, surge in short burst rainfall: Category 3-5 cyclones (extremely severe or super cyclones) are likely to increase in the Sundarbans, affecting cities like Kolkata and Khulna unless the emission level is be controlled at the earliest. Coastal areas and cites, including Kolkata, are expected to be impacted by compound events — several climate phenomena acting together — such as intense cyclones, high sea level rise and an increase in precipitation.
- Sea level rise: The water level in Bay of Bengal close to the Sundarbans is expected to rise 0.6 metres by century-end compared to benchmark of 1995-2014. This is a six-time increase compared to 2021-2040 prediction, which is not only expected to increase erosion and flooding in Sundarban, especially in tandem with high-intensity cyclones and incessant downpour, but also magnify the flooding impact in Kolkata. The Sundarbans have already experienced the highest sea level rise in the country, which is nearly double compared to global average. Kolkata, hardly 100 km away from the Sundarbans, will have to bear the brunt of sea level rise. High tides will become higher.
- Rainfall prediction: The IPCC report showed that ‘one day maximum rainfall’ in Kolkata may increase about 50 per cent by century-end. The city may also record 118 mm of rainfall a day. Total rainfall, however, may rise in the range of 20 per cent compared to present statistics.
- EXAM QUESTIONS: (1) Explain the reasons Kolkata will be at the receiving end of climate change in decades to come. (2) What are "compound events" in the IPCC jargon? How do they affect urban areas? (3) If Kolkata is taken as a case-study, then keeping in mind the IPCC warnings, what are the precautions that Indian coastal areas must exercise from now? Explain in three points.
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