Kinds of fish traditionally indispensable for New Year dishes in Japan are arguably salmon in the east and yellowtail in the west.
The northernmost prefecture of Hokkaido underwent poor autumn catches of salmon, its famous staple, in 2016 and 2017. Meanwhile, yellowtail are now often found in fixed nets installed to catch salmon.
What is said to be behind these phenomena are changes in the marine environment due to global warming. Eventually, local fishermen could be forced to change which fish they catch and the methods they use, and New Year dining tables may also undergo a transition.
On top of global warming, overfishing, plastic pollution and other tough issues are threatening the oceans. Japan has the world's sixth largest territorial waters and exclusive economic zones combined. The country must tackle the crisis head on and exercise its leadership to introduce countermeasures, but it is lagging behind other countries in addressing these problems.
The sustainable development goals of the United Nations adopted in 2015 include the conservation and sustainable use of the oceans. The U.N. program calls for the conservation of 10 percent of coastal and marine areas around countries worldwide by 2020, and already roughly 17 percent of territorial waters and exclusive economic zones (EEZs) fall in this category, but the number for Japan is only 8 percent.
Moreover, Tokyo did not sign up to the Ocean Plastics Charter put together at the summit of the Group of Seven industrialized countries in 2018 in a bid to prevent marine plastic pollution, out of concern for domestic industries and for other reasons.
As a country surrounded by oceans Japan should be ashamed of the current situation. If things continue as they are, we may face a tough backlash such as losing marine harvests.
The sea is hard to warm up and cool down. Heat enough to move up the air temperature of the Earth by 10 degrees Celsius can only increase the ocean water temperature by 0.01 degrees. The impact of global warming will only reach ocean depths very slowly.
However, according to the Japan Meteorological Agency, seawater temperature hikes and drops in dissolved oxygen levels are becoming prominent at a depth of around 2,500 meters to 3,500 meters in the Sea of Japan.
In areas off the coast of Vladivostok in Russia, seawater with high oxygen levels gets cooled down near the surface by seasonal winds during the winter, and the cooled water, which becomes denser, sinks toward the seabed.
According to the National Institute for Environmental Studies, oxygen rich water has not sunk deep in recent years as global warming eased its cooling during the winter. The water near the seabed is feared to lose oxygen in 100 years, triggering a substantial impact on the ecosystem.
The Sea of Japan is detached from other oceans, and tends to be affected by global warming more than the Pacific and other big seas, according to experts. It is therefore vital to collect detailed data including ocean temperatures and oxygen levels from the entire area so that predictions and countermeasures can be established.
However, the Sea of Japan also encompasses the EEZs of Russia, South Korea and North Korea, with lots of political entanglements. Japan cannot simply go ahead and study the area.
The government of Japan should work harder to establish a framework to monitor changes in the Sea of Japan by urging relevant countries to join its project.
--- Use of blue carbon should be promoted
Preventing ocean warming can only be achieved by stopping global warming. Reducing greenhouse gasses is the founding bloc of global warming countermeasures, but Japan can do more as a country surrounded by oceans, such as using "blue carbon."
Blue carbon is the accumulation of carbon on the seabed by marine ecosystems including marine life forms. The material has generated a lot of attention when the United Nations Environment Programme called for its expanded use in a 2009 report.
Just as forests absorb carbon dioxide through photosynthesis, sea grass, kelp and tidelands are important CO2 sinks.
Japan's coastlines reach roughly 35,000 kilometers in total -- almost long enough to circle the planet, and longer than the coastlines of the United States or China. This figure, the world's sixth longest, means Japan has wide coastal areas.
An estimate by the Port and Airport Research Institute says that almost 7 million metric tons of CO2 per year are being absorbed alongside the Japanese coast. This is less than 1 percent of Japan's greenhouse gas emissions, but conserving and expanding seaweed beds to increase absorption alongside the coastal areas would create environments where fish can lay eggs and protect their young children.
The Paris Accord, an international framework to implement global warming countermeasures, requires signatories to complete plans for curbing greenhouse gas emissions, and submit them to the United Nations. According to the port institute, around 30 countries mention the use of seaweed beds as a means to fight global warming. Japan doesn't, but if the country does so, more Japanese people would recognize the importance of the project. The study on the impact of global warming on the sea is still a work in progress. Japan has a responsibility to hand down the world's indispensable oceans in a healthy state to future generations.