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GHG Emissions, Rising Sea Levels, and More Menacing Monsoons
The driver of sea level rises is the Indo-Pacific warm pool, shown in bright orange, which has warmed by 1 degree Fahrenheit -- or .5 degree Celcius -- over the past 50 years, mostly due to human-generated greenhouse gas emissions. Image via NASA Earth Observatory.

The Indo-Pacific warm pool - pictured above in bright orange -- has warmed by 1 degree Fahrenheit, or .5 degree Celsius, over the past 50 years, mostly due to human-generated greenhouse gas emissions. These temperature changes are driving changes in sea level patterns.Image via NASA Earth Observatory.

This season, we’ve been following Mumbai through the monsoon, looking at how monsoon season can ravage transportation systems and batter infrastructure, putting people’s lives and livelihoods in jeopardy.

Now, a new study in Nature Geoscience describes how climate change from greenhouse gas (GHG) emissions is leading to dangerous sea level rises — particularly in the Arabian Sea, the Indian Ocean, and the Bay of Bengal — and potentially heavier monsoon rains, which will aggravate flooding in places like Mumbai.

The study, led by scientists from the University of Colorado at Boulder (CU) and the National Center for Atmospheric Research (NCAR), also in Boulder, finds that the sea level rise is “at least partly a result of climate change.”

More specifically, temperature changes in the Indo-Pacific warm pool — a massive, bathtub-shaped expanse stretching from the east coast of Africa to the International Date Line in the Pacific — are driving the sea level rise.  The pool holds the warmest seawater in the world, and has heated by 1 degree Fahrenheit, or .5 degree Celsius, over the past 50 years, mostly due to GHG emissions.

These emissions are causing changes in two crucial atmospheric wind patterns — the Hadley circulation and the Walker circulation — which determine sea level patterns in the region. Changes in these wind patterns are generating sea level rises significantly higher than the global average along the coastal lines of the Arabian Sea, the Indian Ocean, and the Bay of Bengal, along with islands like Sumatra, Sri Lanka and Java.

In the meantime, these changes are causing the sea level to fall in other places, for instance, the Seychelles Islands and the island of Zanzibar.

According to the authors, “Our new results show that human-caused changes of atmospheric and oceanic circulation over the Indian Ocean region—which have not been studied previously—are the major cause for the regional variability of sea level change.”

A Times of India cartoon makes light of transit troubles during the monsoon with this picture of a "monsoon-proof bike." However, serious attention to monsoon preparedness is essential for affected cities' transit systems. Image via Times of India.

A Times of India cartoon makes light of transit troubles during the monsoon with this picture of a "monsoon-proof bike." However, serious attention to monsoon preparedness is essential for affected cities' transit systems. Image via Times of India.

And lead author Weiqing Han says changes in circulation patterns could also affect precipitation, leading to heavier monsoons in the eastern tropical regions of the Indian Ocean, and dangerous droughts in the western equatorial Indian Ocean region.

Make Transit Systems Monsoon-Proof

This new research highlights not only the importance of sustainable transport innovations to reduce GHG emissions, but also the urgency of ensuring that infrastructure in threatened areas is more “monsoon-proof.”

This is particularly relevant in low-lying coastal areas like Mumbai, which will be affected by both rising tides and increased rains.

While a fully monsoon-proof transit system is extremely difficult, a few changes could make a big difference:

  • Better coordination and streamlining of government agencies responsible for urban infrastructure.
  • More efficient drain cleaning.
  • Enforcing bans on plastic bags. As one of our Mumbaiker readers commented, enforcing bans on plastic bags — on the books but rarely enforced in places like Mumbai — would signify a huge improvement in urban monsoon preparedness, since the bags clog drains and exacerbate flooding.
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