#WhatTheFAQ: World Meteorological Organization says Mumbai is under threat. Here's why

Global mean sea level rose by 4.5 mm per year during the period 2013-22 and human influence was very likely the main driver of these increases since at least 1971: WMO
Pic credits: Edex Live
Pic credits: Edex Live

Climate change and the increase in sea level have always been concerns around the world. What comes as a major concern to India is Mumbai city is under threat due to the rise in global mean sea level. According to a report by World Meteorological Organization (WMO) released on February 15, Wednesday, global mean sea level rose by 4.5 mm per year during the period 2013-22 and human influence was very likely the main driver of these increases since, at least, 1971, as stated in a report by The Economic Times

Additionally, the largest populated city and the Bollywood hub of India has crossed the national capital Delhi to become the most polluted city in India and the second most polluted worldwide after Lahore in Pakistan, as stated in a report by The Hindustan Times. However, what is this global mean sea level? How is it measured? What are the consequences? #WhatTheFAQ is here to give all these details. 

What is global mean sea level?

Global mean sea level is the average height of the entire ocean surface. Further, it is caused primarily by two factors related to global warming: the added water from melting land-based ice sheets and glaciers, and the expansion of seawater as it warms.

How do they measure sea level?

There are two methods to measure the sea level. One by tide gauges and two with satellite altimeters. Also, tide gauge stations from around the world have measured the daily high and low tides for more than a century, using a variety of manual and automatic sensors.

What did the sea level look like in previous years?

As per the WMO's report, the global mean sea level rose by 0.20 m between 1901 and 2018. The average rate of sea level rise was 1.3 mm per year between 1901 and 1971, 1.9 mm per year between 1971 and 2006, and 3.7 mm per year between 2006 and 2018. 

To note, it rose faster since 1900 than over any preceding century in at least the last 3,000 years. The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago), the department said.

What is the future prediction?

Over the next 2,000 years, global mean sea level will rise by about two to three metres if warming is limited to 1.5 degrees Celsius, two to six metres if it is limited to two degrees Celsius and 19 to 22 metres with five degrees of warming, and it will continue to rise over subsequent millennia. In case of very high greenhouse gas emissions (total failure of mitigation), there is a risk of sea-level rise of two metres by 2100 and even 15 metres by 2300, the WMO said.

Which countries are at threat?

Sea level rise threatens several low-lying small islands. With regards to this, it is a major threat for countries namely: India, China, Netherlands and Bangladesh some of which consists of a large coastal population, as stated in a report by PTI. 

According to the WMO report, big cities like Mumbai, Shanghai, Dhaka, Bangkok, Jakarta, Maputo, Lagos, Cairo, London, Copenhagen, New York, Los Angeles, Buenos Aires and Santiago are under threat. Additionally, this is a major economic, social and humanitarian challenge, the report added. 

What the are consequences of the rise in sea level?

Even a slight increase in the sea level can have devastating effects on coastal habitats. It can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, and lost habitat for fish, birds and plants. 

Additionally, higher sea levels are coinciding with more dangerous hurricanes and typhoons that move more slowly and lead to more rain, contributing to more powerful storm surges that can strip away everything in their path. One study found that between 1963 and 2012, almost half of all deaths from Atlantic hurricanes were caused by storm surges.

In a first-ever debate about the global implications of sea level rise, United Nations Secretary-General António Guterres told the Security Council that, "Rising seas pose 'unthinkable' risks to billions around the world, with profound implications for the very fabric of societies." 

Further, “We would witness a mass exodus of entire populations on a biblical scale, and we would see ever-fiercer competition for fresh water, land and other resources,” he warned, as stated in a report by WMO. 

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