How sea level rise is arriving, and will be dangerous

A detailed insight into the potential sea level rise expected in coming decades.

 How sea level rise is arriving, and will be dangerous

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Read more on - Polity | Economy | Schemes | S&T | Environment

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• Latest IPCC report: The August 2021 report by IPCC's working group (AR WG 1 - Climate Change - The Physical Science basis) is a vast scientific review of climate change, and a warning to all for quick action.
• Five pathways to the future: It shows the 5 socio-economic pathways with different GHG emission levels -

1. very low and low - emissions go to near net zero by 2050 or closer by
2. intermediate -
3. high and very high - double today by 2100 and 2050, respectively

• Outcomes: In the intermediate scene, average warming will go beyond 2°C near 2050. Today, it's 1.09°C higher than pre-industrial, and CO2 concentrations are 410 ppm (285 ppm in 1850).
• The coastal threat: More than 70 crore people along coastal regions, and expanding coastal cities, make it important to understand this risk. Sea levels will continue to rise even after emissions stop rising, because oceans respond slowly to warming. And oceans do not revert to normal easily.
• How it rises: Warm ocean waters expand, glaciers on land melt, and ice sheets in Greenland and Antarctica melt.

1. GMSL rose by 2 cm from 1901 to 2018, with average rate of rise being 1.3 mm/yr (1901-1971) and 3.7 mm/yr (2006-2018).  [GMSL - global mean sea level]
2. Earlier thermal expansion, and now glacier and ice sheet melt are the reasons
3. If emissions are low, GMSL rise will be 0.19 m in 2050 and 0.44 m in 2100; in very high scenario, it will be 0.23 m in 2050 and 0.77 m in 2100

• Ice sheet models: Glacier melt is assessed using ice sheet model. They destabilise rapidly as water warms (MISI - marine ice sheet instability). Then ice cliffs fall fast, in a MICI process (marine ice cliff instability). MICI events are not even included in projections!

1. Rapid sea level rise can happen when mass loss of ice shelves happens
2. In the very high emissions scenario, upto 1.61 m SLR by 2100 is possible
3. Thus, there are non-linear dynamics of changes not captured by many models (so SLR upto 2.3 m by 2100 is not impossible)

• Emissions Gap Report: The UNEP EGR warned of a 3°C warming by 2100, double the Paris deal ambition. Beyond that, all models become uncertain.
• Impact on India: Coastal communities will face the heat, literally, through storms and sea level rise, more frequently now. Policymakers may feel they have another 60 to 80 years to build more coastal infrastructure, but they may be wrong. Relaxing coastal regulations is a bad idea, as is happening with all CRZ (coastal regulation zones).
• Summary: Disaster awaits unless the government prepares everyone in the vulnerable areas, and helps them adapt quickly.
• EXAM QUESTIONS: (1) Explain the implications of the five different scenarios envisaged in the IPCC reports 2021, pertaining to sea level rise. (2) What are the five steps the government of India must take, to help coastal Indian communities face the brunt of rising sea levels? (3) Explain the anomalous expansion of water. What does it mean for studies on sea level rise, in general?

Read more on - Polity | Economy | Schemes | S&T | Environment

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