If the sea level rise in "The Wandering Earth" becomes a reality, can humans reverse it?

The hit movie "The Wandering Earth" is a space opera made in China, which has won praise and pride from countless Chinese people.

Among them, global sea level rise is one of the most shocking climate disasters in the movie, and the scene closest to us is Shanghai, which is completely swallowed by floods.

After the sea level rose sharply, only the Oriental Pearl Tower, Jinmao Tower, Shanghai World Financial Center and other towering landmark buildings remained floating on the water, while the rest were swallowed up.

Although this is just a plot in the movie, global sea level rise is happening in reality.

Figure 1. Shanghai on the sea

Source: Movie "The Wandering Earth"

01

Global sea level rise is accelerating

Sea level rise is one of the most significant impacts of global climate change.

According to satellite observation data from the National Aeronautics and Space Administration (NASA), global sea levels have risen significantly since 1993, with an average annual increase of about 0.34 cm.

That is to say, the sea level has risen by 10.25cm in the past 30 years, and the rising speed is accelerating, which is unprecedented in the past 2,500 years.

According to the latest report released in 2022 by the National Oceanic and Atmospheric Administration (NOAA) and other departments, global sea levels are rising at an accelerated rate and are expected to rise by 25 to 30 cm by 2050.

This means that sea levels could rise by the same amount in the next 30 years as they have in the past 100 years.

Figure 2. Global sea level rise trends measured by satellite since 1993

Source: NASA

Figure 3. Spatial distribution of global sea level change since 1993

The blue areas are where the sea level is falling

Orange/red areas are areas of rising sea levels

Source: NASA

02

What are the causes of sea level rise?

Global warming is the most fundamental cause of sea level rise.

For thousands of years, the Earth's climate has remained stable. Like our bodies, the Earth can maintain a dynamic balance of climate through self-regulation, which is one of the most important characteristics of the ecosystem.

Since humans started the industrial revolution, the large-scale use of fossil fuels has caused the greenhouse effect, which in turn has led to a gradual rise in global temperatures. The ocean absorbs more than 90% of the earth's heat, so the global sea level has risen significantly.

So what are the specific reasons?

When it comes to why sea levels are rising, the most direct reason that comes to mind is probably the melting of glaciers.

Indeed, global warming has caused the Greenland Ice Sheet, Antarctic Ice Sheet and mountain glaciers to melt faster, which has caused a significant rise in global sea levels.

Especially before 1940, the melting of glaciers and the Greenland ice sheet was the main cause of global sea level rise.

Subsequently, global dam construction briefly slowed the rate of sea level rise in the 1970s.

However, in addition to the melting of glaciers, there is another factor that is easily overlooked by the public, that is, the thermal expansion of sea water, which is actually the main reason for the rise in sea levels.

Climate warming will increase the temperature of the sea water from the surface to a depth of about two thousand meters. When the temperature is 25℃, for every 1℃ increase in water temperature, a 100m thick sea water layer will expand by about 0.5cm.

Scientific research shows that 42% of the sea level rise between 1993 and 2018 can be attributed to thermal expansion of ocean water, while the melting of land glaciers, the Greenland ice sheet and the Antarctic ice sheet contributed 21%, 15% and 8% respectively.

The thermal expansion of the ocean and the melting of glaciers and ice sheets under climate warming have caused the global sea level to rise at an accelerated rate. Since 1900, the rate of sea level rise has exceeded that of any century in the past 3,000 years and is irreversible on a time scale of hundreds to thousands of years, posing severe challenges to human survival and development.

Figure 4. Global sea level rise and its dominant factors from 1900 to 2018

The black line is from tide gauge observation data

The orange line comes from satellite observation data

Source: NASA

03

What harm will rising sea levels bring?

The accelerated rise in sea levels has directly caused coastal areas to become severely affected areas, and the severity of marine disasters is also increasing.

Coastal areas are the most economically developed and densely populated areas in the world, with about one-third of the world's population living within 60km of the coast.

According to research published in the journal Nature Communications, by the middle of this century, about 150 million people will be living on land below sea level.

If the sea level continues to rise, it will directly lead to serious survival crisis for people living on land below sea level, flooding of low-lying areas in coastal areas and loss of land resources. Some coastal countries will even be completely submerged by sea water.

For example, Tuvalu, a Pacific island country most typically affected by rising sea levels, has seen its sea level rise by nearly 10cm between 1993 and 2009, with an annual sea level rise of about 0.5cm. Its rate of rise is four times the global average.

In 2001, Tuvalu decided to relocate its entire nation to New Zealand, becoming the first country in the world to abandon its homeland due to rising sea levels.

Climate risks associated with rising sea levels include increased intensity and frequency of typhoons and more rainfall, which will intensify storm surges, coastal erosion, floods and other disasters in coastal areas.

Coastal ecosystems such as mangroves, salt marshes, and seagrass beds, which are sandwiched between the ocean and the coastal protection system, are also facing the risk of being continuously squeezed, gradually reduced, or even disappearing. This is also an ecological problem faced by coastal countries in common.

As one of the sensitive areas to global warming, my country is also facing a serious problem of rising sea levels.

According to the 2021 "China Sea Level Bulletin" released by the Department of Marine Early Warning and Monitoring of the Ministry of Natural Resources, the sea level along the coast of my country rises by 3.4 mm each year. The sea level in 2021 exceeded that of previous years by 84 mm, setting a record high since 1980.

The long-term cumulative effect of sea level rise has caused the squeezing of my country's coastal ecosystem and the loss of tidal flats. It has also seriously affected coastal underground freshwater resources and increased the severity of disasters caused by storm surges, coastal city flooding and saltwater intrusion.

In addition, land subsidence in coastal areas has led to a rise in relative sea level, increasing the impact of the disaster.

In 2021, my country's marine disasters were mainly storm surges, waves and sea ice disasters, causing a total direct economic loss of about 3.071 billion yuan and 28 deaths and missing persons. The worst-hit region was Zhejiang Province, where economic losses accounted for 31% of the total losses from marine disasters.

Figure 5. Sea level changes along China's coast from 1980 to 2021

Source: China Sea Level Bulletin 2021

Figure 6. Flooding near the Yongjiang Bridge in Ningbo, Zhejiang during a storm surge

Source: China Sea Level Bulletin 2021

04

Can carbon neutrality stop sea level rise?

Addressing global warming is a fundamental measure to address the problem of rising sea levels.

Greenhouse gases such as carbon dioxide are the "culprits" of global warming. They surround the earth's surface like a "blanket". The thicker this "blanket" is, the faster the earth's temperature rises.

Therefore, if we want to cool the earth, reducing greenhouse gases such as carbon dioxide in the atmosphere is key.

In order to jointly respond to the challenges of climate change and slow down the trend of global warming, countries around the world have reduced greenhouse gas emissions through a global agreement and set a target for controlling the rise in global average temperature through the Paris Agreement.

That is, to control the global temperature rise in the 21st century to within 2°C above the pre-industrial level, and seek to further control the temperature rise to within 1.5°C.

In this context, as the world's second largest economy and the largest carbon dioxide emitter, my country has proposed a "dual carbon strategy", namely:

1️⃣ “Carbon Peak”: Carbon dioxide emissions will no longer increase before 2030, and will gradually decrease after reaching the peak;

2️⃣ "Carbon neutrality": By 2060, carbon dioxide emissions and absorption will be balanced, positive and negative offsets will be achieved, and relative "zero emissions" will be achieved.

Many countries in the world have also announced the goal of achieving full carbon neutrality between 2050 and 2060, such as the European Commission, Japan and South Korea.

At present, there is basically a consensus on achieving carbon neutrality globally.

Some people may ask: If the carbon neutrality goal is achieved, carbon emissions are balanced with carbon absorption, and the temperature no longer rises, will the sea level stop rising or even fall?

According to a report from the National Center for Atmospheric Research (NCAR), if global greenhouse gas emissions remain stable and global temperatures no longer increase, sea levels will still rise for hundreds of years, mainly due to the thermal expansion of seawater.

In fact, there is a temperature difference between the upper sea water and the deep sea water. When the temperature of the deep sea water rises, it will cause the upper sea water to expand, and the volume of the sea water will increase like a sponge, causing the sea level to rise by 1m or tens of meters.

Sea level will stop rising only when the sea water temperature is exactly the same as the atmospheric temperature, and it will take about 300 years to reach this equilibrium state.

So the answer is: achieving carbon neutrality cannot completely stop or reverse global sea level rise.

Global warming has caused the sea level to rise rapidly, which not only poses great risks to low-lying, coastal areas and small island countries, but also seriously disrupts the ecological balance of nature.

Sea level rise and its related disasters are one of the major challenges to the sustainable development of future human society and economy.

Although carbon neutrality is unlikely to reverse the rise in sea levels, if the "dual carbon strategy" is not adopted, global sea levels are expected to rise another 1.4 m by 2100, and the coastal economic zones of countries around the world will suffer a devastating blow by then.

Therefore, the strategic significance of implementing "carbon peak" and "carbon neutrality" is very important.

When the earth's environment, on which we depend for survival, suffers a catastrophic disaster, what should humanity do?

If what happens in the movie really happens, once the Wandering Earth plan is launched, it means that the earth's climate will enter "hell mode" and become completely uninhabitable, and humans will be forced to face wandering.

Carbon neutrality is a topic concerning the shared future of mankind.

In order to protect our home planet, carbon neutrality will be the common choice of all mankind in the future.

END

Author: Zhang Meinan

Chinese Academy of Forestry

Institute of Forest Ecology, Environment and Nature Conservation

Editor: Guru