How changes in the level of Arctic sea ice can change monsoon patterns in India

(Source – The Hindu, International Edition – Page No. – 11)

 Impact of Arctic Sea Ice on the Indian Monsoon:

Introduction to the Indian Monsoon

• In recent years, erratic and unpredictable rainfall has plagued the Indian monsoon, causing droughts and floods.
• Climate change is a significant driver, but a complex interaction of multiple climatic factors also contributes to these changes.
• A new study, published in Remote Sensing of Environment by Juhi Yadav et al., from the National Centre for Polar and Ocean Research (NCPOR), and South Korea’s Korea Polar Research Institute, reveals that seasonal variations in Arctic sea ice also impact the Indian summer monsoon rainfall (ISMR).
• Various studies suggest that the declining Arctic sea ice due to climate change affects the ISMR.

Mechanics of the Indian Summer Monsoon

• The ISMR, active from July to September, is one of the world’s most notable monsoon systems, responsible for bringing significant rainfall to the Indian subcontinent.
• As the summer months approach, the Central Asian and Indian landmass heats up more rapidly than the surrounding oceans.
• This creates a low-pressure zone, which pulls in moisture-laden winds from the ocean.
• The southwest monsoon, after crossing the equator, splits into two arms: one brings rain to India’s western coast via the Arabian Sea, while the other impacts the eastern and northeastern regions from the Bay of Bengal.
• The ISMR system is more complex than initially thought, influenced by ocean surface temperatures, pressure gradients, atmospheric waves, and the circum-global teleconnection (CGT), a wave pattern in the mid-latitudes.

Findings of the Study

• Central Arctic Sea Ice Impact:
  • Reduced sea ice in the central Arctic leads to less rainfall over western and peninsular India but increases rainfall in central and northern regions.
• Barents-Kara Sea Region Impact:
  • Low sea ice in the Barents-Kara Sea region delays the monsoon’s onset and makes it more unpredictable, impacting rainfall patterns.

Atmospheric Systems Influencing Monsoon Patterns

• Rossby Waves and Their Effect:
  • When sea ice in the central Arctic increases, heat transfers from the ocean to the atmosphere, triggering cyclonic circulation in lower latitudes.
  • This strengthens Rossby waves, which influence weather patterns globally. The Rossby waves enhance high pressure over northwest India and low pressure over the Mediterranean, affecting the subtropical easterly jet over India.
  • This results in an anomalous high-pressure system over Central Asia, causing more rain over western and peninsular India.

• Barents-Kara Sea Ice Decline:
  • Low sea ice in the Barents-Kara region triggers high pressure over southwest China and leads to a positive Arctic Oscillation.
  • The reduced sea ice also leads to anticyclonic circulation over northwest Europe, disturbing atmospheric stability in subtropical Asia and India.
  • This results in high rainfall over northeastern India but drier conditions in central and northwest India.

The Role of Climate Change

• Climate change has intensified the reduction of Arctic sea ice, exacerbating the variability and unpredictability of the ISMR.
• As sea ice levels continue to drop, more frequent and severe droughts, alongside excessive rainfall and flooding, are likely in different regions of India.
• The study underscores the importance of Arctic sea ice in influencing global climate systems, with direct effects on the Indian monsoon.

Conclusion

• The findings highlight the intricate relationship between Arctic sea ice and the Indian monsoon, showcasing how far-reaching the effects of sea ice loss can be.
• The study emphasises the need for more extensive research into these climate dynamics and the necessity for accurate forecasts to anticipate monsoon variability in the future.