The waters will rise near Bombay

Rising sea levels materially change our thinking about coastal real estate on a 25-year horizon

- AJAY SHAH

There has been a deceleration in the global policy work on decarbonisation, starting in the first Donald Trump presidency in the US (2016) and then Russia's invasion of Ukraine (2022). The outlook on emission is now more challenging. We all have to shift from planning on something near the median scenario to something closer to the high-emission scenarios.

What does this mean for Bombay? In high-emission scenarios computed by the International Panel for Climate Change, the sea level at Bombay is likely to rise by about 25cm by 2050. This reflects the thermal expansion of sea water and the global melting of ice in a warmer world.

Alongside this, there is a local geological phenomenon that affects Bombay, which is subsidence. Bombay is subsiding by around 2mm per year. This reflects factors including sediment compaction, groundwater extraction, and the load of the urban built environment upon the reclaimed land. This phenomenon is likely to add about 5 cm to the rising waters by 2050. Putting these together, the sea level at Bombay is likely to rise by about 30 cm or about 12 inches.

When we look beyond 2050, high-emission scenarios are much worse than the median scenario. So we should think that the waters will rise by about 12 inches to 2050 and then things will get much worse to 2100.

In a swimming pool, we can readily visualise a water level that's about 12 inches higher. We tend to visualise ourselves standing at the Aksa beach, and water at the knees reaching up to the waist. But the sea is not a swimming pool. It is full of motion. When the average sea level rises by a small amount, this has big implications for the urban environment.