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A quarter of the coastal land of China will sink below sea level within a century, putting hundreds of millions of people at risk of being flooded, due to land subsidence and climate change, according to a new study, published in the journal Science on Friday (April 19).
The land subsidence in China is primarily a result of rapid urbanisation — activities such as excessive groundwater extraction and the weight of buildings lead to subsidence. The situation has been exacerbated by climate change, which is resulting in the rise of sea levels.
Sea level rise isn’t just limited to China. It is a global issue that is projected to affect between 130 million to half a billion people depending on different temperature scenarios in the long run, according to a UN report.
So, how is climate change leading to sea level rise? Why does it matter? We take a look at these questions in this week’s edition of Warming up to Climate Change — a series of explainers, in which we answer some of the most fundamental questions about climate change, the science behind it, and its impact. You can scroll down to the end of this article for the first 10 parts of the series.
The global sea level has risen by about 8–9 inches or 21–24 centimetres since 1880, according to a report by the National Oceanic and Atmospheric Administration (NOAA). But the more worrying sign is that since 1993, the rate of increase has been accelerating. It has more than doubled from 0.07 inches or 0.18 centimetres per year in 1993 to the current rate of 0.17 inches or 0.42 centimetres per year.
Global average sea level rose by about 0.3 inches or 0.76 centimetres from 2022 to 2023. Experts said there was a huge jump in global sea level between the two years mainly due to the development of El Niño, a weather pattern associated with warmer oceans, in June 2023. Now that El Niño is weakening, the rate of sea level rise is expected to slow down.
“Current rates of acceleration mean that we are on track to add another 20 centimetres of global mean sea level by 2050, doubling the amount of change in the next three decades compared to the previous 100 years and increasing the frequency and impacts of floods across the world,” according to Nadya Vinogradova Shiffer, director for the NASA sea level change team and the ocean physics program in Washington.
The key driver behind rising sea levels is global warming. As temperatures across the world continue to soar, more and more glaciers and ice sheets are melting and adding water to the ocean. Global warming is also making the ocean warmer, which is leading to something called thermal expansion — when water becomes warmer, it expands in volume. This is contributing to sea level rise as well.
The NOAA report said from the 1970s till the last decade or so, melting and heat expansion were contributing roughly equally to observed sea level rise. The melting of mountain glaciers and ice sheets, however, has accelerated. For instance, a 2023 study found that glaciers in Greenland were melting five times faster than in 20 years.
Therefore, the amount of sea level rise due to melting between 2005 and 2012 nearly doubled in comparison to the amount of sea level rise due to thermal expansion, according to the NOAA report.
The most visible consequence of sea level rise will be the flooding of coastal areas. Take the example of coastal cities in India. A 2022 analysis by RMSI, a global risk management firm, found that some critical properties and road networks in Mumbai, Kochi, Mangalore, Chennai, Visakhapatnam, and Thiruvananthapuram will be submerged by 2050. The sea level along the Indian is rising at an average rate of about 1.7 mm per year with 3.3 mm per year in the recent decades (1993-2015), according to a response by the Ministry of earth sciences in Lok Sabha in 2021.
Things are worse for island countries like Indonesia. In 2019, Indonesia announced that the country’s capital would be relocated from Jakarta, which is prone to flooding, to the province of East Kalimantan on the island of Borneo.
The rise of sea level also leads to more intense storm surges — the rise in seawater level caused solely by a storm — flooding, and damage to coastal areas. That’s because higher sea level can allow more water inland during hurricane-related storm surges.
With sea level rise, saltwater contaminates freshwater aquifers, many of which are used by communities for agricultural and drinking purposes.
Here are the previous instalments of the series: part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, and part 10.
