Heatwaves linked to man-made climate change

Heatwaves linked to man-made climate change

Subject: Environment

Context- India is gripped in the wrath of a long spell of heatwaves that too in the early month of April.

Concept-

• Three eminent scientists with expertise in how atmospheric, land and ocean systems were influenced by greenhouse gas emissions, drew upon their decades of research to explain how the accumulation of greenhouse gases in the atmosphere exacerbated temperatures in the oceans and the land and caused increased glacier melt, heightened sea level rise and led to changes in the biosphere.

What is a Heatwave and when is it declared?

• A heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western and South Central parts of India.
• It is a condition of air temperature which becomes fatal to the human body when exposed.
• The IMD declares a heatwave when the maximum temperature crosses a certain threshold — 40°C in the plains, 37°C along the coast, and 30°C in hilly regions.
• Alternatively, a heatwave is declared if the maximum temperature rises by between 5°C and 6.4°C above normal.
• A severe heatwave is declared when the maximum temperature rises more than 4°C above normal.
• A third condition for a heatwave arises when an area records a maximum temperature of more than 45°C and up to 47°C on any given day.

How are they formed?

• Heatwaves form when high pressure aloft (3,000–7,600 metres) strengthens and remains over a region for several days up to several weeks.
• This is common in summer (in both Northern and Southern Hemispheres) as the jet stream ‘follows the sun’.
• On the equator side of the jet stream, in the upper layers of the atmosphere, is the high pressure area.
• Under high pressure, the air subsides (sinks) toward the surface, warming and drying adiabatically, inhibiting convection and preventing the formation of clouds.
• Reduction of clouds increases shortwave radiation reaching the surface.
• A low pressure at the surface leads to surface wind from lower latitudes that brings warm air, enhancing the warming.
• Alternatively, the surface winds could blow from the hot continental interior towards the coastal zone, leading to heat waves.

**** For Further Reading Refer To Optimize Ias DPN 28 April 2022.