Producer: Popular Science China
Producer: Lin Tao (Popular Science Author)
Producer: Computer Network Information Center, Chinese Academy of Sciences
From a bird's-eye view from space, the Earth as a whole appears beautiful azure. The vast and deep ocean, covering 71% of the earth's surface area, is a unique beauty in the universe.
A complete view of the Earth taken by the gose-8 meteorological satellite in geostationary orbit (Image: NASA)
The oceans are the source of life, the great climate regulators, and vital to our planetary home. However, in the context of a warming climate, global sea levels are also rising continuously, posing serious challenges to the survival and development of human society.
Research by the National Oceanic and Atmospheric Administration of the United States shows that global sea levels have risen by 21-24 centimeters today compared to 1880. And for every 1°C increase in global temperature, sea levels rise by 2.3 metres. By 2100, global temperatures are expected to rise by 2 to 5°C and global sea levels by 1 metre.
1993-2020 satellite measured global sea level change, an average annual increase of 3.3 mm (Image: nasa Goddard Space Flight Center)
The most obvious consequence of continued sea-level rise is the collapse of coastlines, the erosion of land and the loss of some coastal areas.
The scene from the sci-fi movie Futurama Water World is not alarmist. According to research published in the journal Nature, by mid-century, about 150 million people will live on land below sea level, with Pacific island nations such as Kiribati and Tuvalu bearing the brunt.
If the situation continues to deteriorate, even the world's major coastal cities, such as Shanghai, Tokyo, New York, etc., may be submerged. Some large countries with vast hinterlands still have room to turn around, and small countries such as the Netherlands and Singapore will disappear from the map if they face the worst outcome.
Suppose a dynamic simulation of sea level rise along The coast of China after the melting of global land glaciers
Shenzhen and Hong Kong, Taiwan, Yangtze River Delta (Source: Reference 2)
What causes sea level rise?
It is often assumed that the cause of sea-level rise is glacier melting, but a report from the United Nations' Intergovernmental Panel on Climate Change (IPCC) subverts that view – the main cause of sea-level rise is not glacier melting, but the thermal expansion effect of seawater.
This deceptively simple phenomenon of thermal expansion and contraction contributed 42% to the rise of sea levels. By comparison, land glaciers melt only 21 percent. So, what is the heat expansion of seawater?
According to a joint study by the Institute of Atmospheric Physics of the Chinese Academy of Sciences and the National Center for Marine Environment Forecasting, in 2018 alone, the heat content of 2,000 meters of seawater in the upper layer of the Earth's ocean increased by 0.91×10^22 joules compared with 2017 – equivalent to 388 times China's annual power generation in 2017, or 100 million times the energy released by the atomic bomb explosion in Hiroshima. With such a huge increase in heat content, the volume of seawater will be heated and expanded.
It is worth mentioning that the huge amount of fresh water released by the melting of glaciers will increase the water vapor content in the atmosphere, and water vapor has a very obvious greenhouse effect, which in turn will increase glacier melting, forming a vicious circle that we do not want to see.
Several studies in recent years have generally revealed the fact that sea levels are not only rising, but also rising at an accelerating rate.
What are the consequences of rising sea levels?
As sea levels rise, the most intuitive result is that coastlines collapse and land encroaches. But the cascading by-products of sea-level rise should also be alarmed.
1. Exacerbate climate change
The intensification of climate change is difficult to quantify, but the implications are far-reaching. As a huge surface heat reservoir, the ocean plays a very important role in the earth's climate movement. The circulation of ocean currents inside the ocean, as well as the cycle of heat and water vapor between sea, land and air, has shaped the natural landscapes and complex and diverse weather phenomena on the earth.
But in the context of the current global warming, the rise and fall of the surface area of the sea and land will disrupt the already fragile heat balance. The amount of transpiration and heat storage in the oceans may trigger climate instability and increase the probability of extreme weather events.
Global Ocean Surface Temperature Anomaly Level Analysis (June-September 2021) (Credit: National Oceanic and Atmospheric Administration)
2. As sea levels rise, the impact of catastrophic storm surges will be more pronounced
The intensification of flood disasters will increase the difficulty of discharging pollutants, resulting in a shortage of available freshwater resources along the coast, which will adversely affect the sustainable social and economic development and people's production and life.
3. The ecological environment is threatened
Affected by rising sea levels and coastal protection obstacles, the habitats of intertidal species are compressed, which in the long run will lead to biodiversity damage, degradation of ecosystem functions, and changes in species abundance and biome structure.
A 2016 study by the University of Queensland in Australia showed that rising sea levels had led to the extinction of a naked-tailed rat living on the Great Barrier Reef.
In addition, there is a phenomenon that cannot be ignored in some coastal areas: the ground subsidence caused by over-exploitation of groundwater will reduce the surface relative to sea level, and objectively increase the disaster risk of sea level rise.
The most typical example is Jakarta, the extremely densely populated capital of Indonesia.
Not only is Jakarta at about 40 per cent below sea level, but ground subsidence in Jakarta is getting worse. As a result, the Indonesian government proposed a 2024 relocation plan to relocate the capital to Kalimantan, a process that will cost nearly $40 billion, but this is also a last resort under the trade-offs.
Rising sea level exacerbates waterlogging in Jakarta (Image: Indonesia State News Agency)
What can humans do?
To cope with rising sea levels, humans need to prepare in advance.
The first is to improve the capacity of sea level monitoring, early warning and risk assessment. Information collection and analysis on sea level changes can be strengthened by satellites, etc., and early warning monitoring and vulnerability assessment can be carried out to provide decision-making basis for the preparation and revision of construction plans and disaster plans;
The second is to improve the disaster prevention and mitigation functions of the coastal zone. While paying attention to ecological development, we will build a three-dimensional protection system, heighten and strengthen facilities such as breakwaters, and build and drain flood facilities.
Breakwater on the outskirts of The Palm Dubai, both aesthetic and protective (Image: Dubai Tourism Board, UAE)
However, these measures have only a temporary bailout function. To fundamentally solve the problem of sea level rise, it is still necessary to focus on the core point of climate change and alleviate the greenhouse effect by reducing carbon emissions.
A 2019 report by the United Nations Intergovernmental Panel on Climate Change (IPCC) found that humans need to remove 100 billion to 1 trillion tons of carbon dioxide from the atmosphere by 2100 to limit global warming to 1.5°C to avoid a series of climate catastrophes.
In response to climate change, China has also set a goal of reaching a carbon peak by 2030 and achieving carbon neutrality by 2060.
Responding to rising sea levels requires global solidarity.
bibliography:
（1）rebecca lindsey. climate change: global sea level. noaa. 2021.01.25.
（2）www.chinafile.com/reporting-opinion/environment/submerged?utm_source=asia+society&utm_campaign=327cf83d9f-enews_150602&utm_medium=email&utm_term=0_de00ad8d9d-327cf83d9f-170713053.
（3）cheng, l. j., and coauthors, 2019: 2018 continues record global ocean warming. advances in atmospheric sciences., 36(3).
(4) 2020 China Sea Level Bulletin. Department of Marine Early Warning monitoring, Ministry of Natural Resources. 2021.04.
(5) Special Topics for Marine Disaster Prevention and Mitigation: Sea Level Rise. National OceanOgraphic Information Center. 2011.05.06.
(6) Technical guidelines for the assessment of vulnerable areas affected by sea level rise. hy/t 227-2018. National Technical Committee for Marine Standardization. 2018.02.13.