Potential Effects of Sea Level Rise on Japan

In the heart of present-day Osaka, Namba’s entertainment district is stacked with clubs, restaurants, and eateries. Jumbo animatronic signs promise tourists a variety of fried and sauced culinary delights. Overflowing garbage cans spill onto the pavement and the heavily canalized river reflects the light of stories-tall neon signs, announcing their building’s occupants. Grimey vendors abut the sterile whiteness of H&M and the manicured lamplight of a multi-story Starbucks. Geographically Namba is not huge, but thick crowds defy anyone hoping to traverse it quickly. The name “Namba” is often written in hiragana, the Japanese syllabary, obscuring it’s etymology. It’s Chinese characters, however mean “difficult waves”, a reference to Namba’s past.

Thousands of years ago large swaths of modern Osaka were under water. A massive lake, Kawachi-ko, once stretched from the Seto Inland Sea deep into the modern city centre and extended north towards Kyoto. Namba was a port on this lake. Paved and built, nothing of Kawachi-ko remains today; much of Osaka is constructed on reclaimed land. Wedged between crowds of tourists, the gently-waving crab and illuminated fugu signs are the only reminders that Namba is a mere seven kilometres from the sea. According to recent climate projections however, this may change.

The world is on track for a 3.2C increase in global temperature by 2100⁽¹⁾. According to some projections, this could raise the median sea level by as much as 6.4 meters, which is far above the relative safety of the 2C threshold set out by the Paris Climate Agreement⁽²⁾. In Osaka alone, over 5.2 million people would be affected by this rise in sea level. Both Namba and Umeda, Osaka’s prime business districts, would be submerged, lost forever⁽³⁾.

Imagine a block of ice weighing the same as Mt. Everest– 83 gigatons– melting into the ocean over the course of a two year period. Then imagine another, and another, each melting into the sea every two years. This not a hypothetical possibility, but the already-observed melting of the Amundsen Sea Embayment, just one region of the Antarctic, over the course of a twenty-year observation, published in 2014⁽⁴⁾. As the planet warms, huge quantities of water frozen in glaciers thaws and flows into the sea. Currently 90% of glaciers worldwide are shrinking.

Greenland and Antarctica, both massive ice sheets, are the largest areas of glacial melting, and two of the main contributors to sea level rise⁽⁴⁾. The Greenland ice sheet is 3km thick in some places and were it to melt entirely, would raise sea levels around the globe by more than 6 meters. The Antarctic ice sheet meanwhile, is on average 2km thick and constitutes 90% of the world’s ice. If it melted completely, sea levels would rise by 600 meters⁽⁴⁾. The prospect of either the Greenland or the Antarctic melting entirely is extremely unlikely. However they are melting, and the speed at which they are melting is extremely disturbing.

Glacial runoff contributes to rising seas in two ways. First by directly increasing the amount of water in the oceans. After the water flows into the sea however, it continues warming. As water heats, it gets bigger. Globally, oceans absorb about 90% of increased atmospheric heat⁽⁵⁾. This expanding water accounts for about half of the sea level rise in the last century. As temperatures increase and sea levels rise further, all of these processes speed up.

The most obvious effect of sea level rise will be on beaches. Already increasing at a rate of about 5mm per year, oceans gradually creep over the sands⁽⁶⁾. The waves continually pounding the beaches advance, eroding coastlines. Homes and businesses, once enviable for their view of the shore, will be inundated. Just a 0.3m rise would eliminate 50% of Japan’s sandy beaches, while a 1m rise would overwhelm 90%⁽⁶⁾. As humans will be forced to relocate, animals, fish, and plants will also see their habitats flooded.

Meanwhile, and less visibly, seawater creeps into deltas and up rivers, decreasing their freshwater content and solidifying coastal soils. This sea water, denser than freshwater, travels through tiny pores into Japan’s aquifers. Called saltwater intrusion, this process contaminates groundwater, making it saltier. Saltwater is no good to drink and no good for rice. While difficult to predict, Central and Southern Japan could see a 40% decrease in rice yields due to climate change⁽⁶⁾. While this decrease is not all the direct result of sea level rise–increased levels of CO2 also play a role– a 2015 study in Bangladesh found that as rivers and soil get saltier, as much as 15.6% of it’s annual rice-yield could disappear⁽⁴⁾.

Climate change will also make once-extreme events worse. As the climate warms, more water vapour evaporates into the air. Downpours become stronger, and storms more powerful. Typhoons, fed by warmer waters, increase in strength. Moving toward land, typhoons push a swell of water in front of them. This swell– storm surge– is the most destructive part of the typhoon. When it combines with a natural high tide, it’s height can reach over six meters⁽⁵⁾. Waves rush inland, battering structures, flooding neighborhoods, and taking lives. Global warming will make these extreme events more likely, and once remarkable storm surges will become commonplace⁽⁴⁾⁽⁶⁾.

Japanese cities have a lot to lose from 3C of sea level rise. 46% of Japan’s population and 47% of Japan’s industrial output are at risk from sea level rise and associated typhoons and storm surges. While all of Japan’s largest cities are at risk from sea level rise, the effects will be felt unevenly. The populations of Tokyo, Osaka, and Nagoya risk the most from a 3C rise, and have the most to gain from limiting climate change to 2C⁽²⁾.

People in affected areas will have to move, stressing non-affected areas, and local communities will be uprooted. The economic impacts of these changes will be immense. A report based on OECD data projected that in 2070, Tokyo is at risk of losing more than $1.2 trillion in infrastructure due to flooding. Osaka-Kobe will see $970 billion in at-risk assets, and Nagoya will see over $620 billion⁽⁷⁾.

Outside Japan, sea level rise will also cause huge regional disruption. Eight of the world’s ten largest cities are coastal, and over 275 million people internationally live in urban areas that will be flooded given 3C warming⁽²⁾. While the chaos unleashed by climate change will be global, Asia will be disproportionately affected. 58.3% of affected cities in the Climate Central data-set are in Asia, and ten of those are Japanese. Although globally, Shanghai will be the hardest-hit city, all of Japan’s neighbors will have to contend with sea level rise.

According to the IPCC, an intergovernmental report on climate change, “Climate change can indirectly increase risks of violent conflicts in the form of civil war and inter-group violence” as well as increasing the severity of poverty and economic crises⁽⁴⁾. Regionally, this will likely mean higher levels of migration, as well as increasing competition over natural resources⁽⁸⁾.

Asia is the most populous region globally, while also being the most affected by natural disasters. Climate change is likely to take the heaviest toll on the region⁽⁸⁾. Despite it’s currently restrictive immigration policy, Japan will not be immune from the effects of shifting populations. Between regional instability, changing levels of food security, and the direct displacement of its own citizens, 3C sea level rise will radically alter Japan. It is critical that planning for these scenarios begins now.

In Osaka, the municipal government’s environmental bureau says that it expects that Osaka will be affected by climate-related natural disasters and is discussing preventative measures, but has yet to investigate the full extent of the risk. The results of government planning will be pitted against whatever degree of climate change we choose as a society, either through conscious choice or inaction.

Using the map below, explore the effects of rising seas around Japan, and see how different levels will affect communities.