New IPCC report warns of marine heat waves, extremely severe cyclones


Pune, September 26: The Intergovernmental
Panel on Climate Change
(IPCC) on Wednesday released a Special
Report on Oceans and Cryosphere in a Changing Climate
. It is the first
such report exclusively addressing the impacts of a warming world on the oceans,
and cryosphere—the parts of the earth covered by glaciers, sea ice and permafrost.
The report has significant messages for India.

The report focuses on the emergence of
ocean extremes in response to increasing carbon emissions due to continued burning
of fossil fuels. The extremes include marine heat waves, extreme El Niños, and extremely
severe cyclones. These ocean extremes are new to our world, and have far
reaching impacts, especially on India and the Indian Ocean-rim nations.

Take for instance extreme El Niños.
In 2015–16, we had one of the strongest El Niños recorded in modern
instrumental history. El Niños generally occur every 2-7 years, and are characterized
by warm ocean temperatures in the east Pacific which affect the global weather.
For India which depends on the monsoon rains, a moderate El Niño in itself can
result in a deficit and erratic monsoon. So, when an extreme El Niño hit the
globe in 2015–16, India reeled under back-to-back droughts. Ethiopia and South
Africa had one of the worst droughts in 50 years and severe heatwaves,
resulting in a massive shortage of food grains.

Such extreme El Niños are likely to
increase in the future – from one event every 20 years during 1891–1990, to one
every 10 years by the end of the century. This may have an immense impact on
future monsoons and the heavily agrarian based society in India and South Asia
in large.

Now, the next monster is something totally
new—marine heat waves. These are heatwaves over the ocean, much similar to that
over the land. They are ocean’s erratic response to increased warm waters.
Worst, they often co-occur with extreme El Niños. Marine heat waves hit the sea
life the hardest. Coral reefs occupy only 0.1% of the planet’s surface, but are
home to 25% of all the animals found in the ocean. Corals have a specific range
of temperatures that they can survive in, and frequent occurrence of marine
heat waves could kill them and the ecosystem around them. Due to these heat
waves, aquaculture industries along the Indian Ocean-rim have suffered severe
damage due to fish mortality in recent years.

Satellite observations reveal that marine
have very likely doubled in frequency between 1982 and 2016,
and that they have also become longer-lasting, more intense and extensive. If
current carbon emissions are not reduced, a one-in-hundred-day event (at
preindustrial carbon dioxide levels) is projected to become a one-in-four-day
event by 2031–2050 and a one-in-two-day event by 2081–2100.

Along with the marine heat waves, the temperature,
sea level and acidity are increasing, while oxygen is decreasing in the Indian
Ocean. The Indian Ocean has been unusual in terms of relatively low oxygen
below the surface and yet having a relatively high surface production.
Near-surface deoxygenation is bad news for this high productivity.

All these changes have heavily impacted
coastal wetlands, resulting in increased mortality of vegetation, loss of
habitats, changes in community and ecosystem structure. The IPCC report also
points out a loss of coastal blue carbon habitat—seagrasses, mangroves and
marshes which assist in carbon sequestration. Potential fisheries catch in the
Indian Ocean have already been hit by the effects of warming and changing
primary production on growth, reproduction and survival of fish stocks.

The third byproduct of ocean warming is extremely
severe cyclones. The probability of post-monsoon tropical cyclones over the
Arabian Sea has increased. Cyclone Nilofar in 2014, for instance, was the first
extremely severe cyclone to be recorded in the Arabian Sea in the post-monsoon
cyclone season. Though the cyclone did not make landfall, it produced heavy
rainfall on western Indian coasts. With a rapidly warming Indian Ocean, such severe
cyclones are projected to increase in number and we cannot overlook the
possibility of them making landfall over the west coast of India.

Unlike the United States which is showing
wobbling response to climate change at the federal level with the climate
action left to the mercy of states, India is far ahead in developing and
implementing mitigation and adaptation strategies realizing that global warming
is at its doorstep. India has constituted the National Climate Change Action
Plan and has promised to ramp up huge investments in renewable energy sector.
However, much more needs to be done. India can take up global warming as an
opportunity and emerge as leader by advancing science and development in ocean-based
renewable energy resources, energy-efficient coastal and offshore infrastructure
and capitalize on its 5000 km coastline for green transportation, while
adapting to the changing climate.

By Roxy Mathew Koll and Raghu Murtugudde

(India Science Wire)

[Roxy Mathew Koll is climate scientist at Pune-based Indian Institute of Tropical Meteorology and a lead author of the IPCC Special Report on Oceans and the Cryosphere. Ra ghu Murtugudde is a professor of atmospheric and oceanic science and earth system science at the University of Maryland, and a visiting professor at IIT Bombay.]

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