A report on climate change in Japan released on March 26 warns that if temperatures continue to rise significantly, the nation could experience once-in-a-century heat waves annually.
The report, jointly released by the Japan Meteorological Agency and the science ministry, is intended to help the central and local governments in their climate change measures.
The study marks the second conducted since the first report was released in 2020.
The central government has been working to reduce greenhouse gas emissions to virtually zero by the year 2050.
However, the current average temperature in Japan has already risen 1.3 degrees above the level at the beginning of the 20th century, the benchmark year.
The report estimated future projections under two assumptions.
The first is the “4-degrees scenario,” which assumes that the global average temperature will rise 4 degrees above pre-industrial levels.
The second is the “2-degrees scenario,” which assumes that the increase is limited to 2 degrees, as included in the Paris Agreement, the international accord to combat climate change.
Under the 4-degrees scenario, temperatures in Japan at the end of the 21st century will be 5.1 degrees higher than at the beginning of the 20th century, the report predicted.
The number of "nettaiya" (tropical nights) per year, when the minimum temperature from the evening to the next morning is 25 degrees or higher, which currently stands at about 25, would double to about 56.
On the other hand, under the 2-degrees scenario, Japan’s temperature rise would be 2 degrees and the number of tropical nights would be limited to about 26 days.
These are average values for locations where the effects of urbanization and other factors are relatively small.
In Tokyo, however, the effects will be even more pronounced.
Under the 4-degrees scenario, the temperature will rise 6.2 degrees by the end of the 21st century, and the number of tropical nights will increase from the current 32 per year to approximately 92.
Extreme weather disasters will also become more frequent, the report said.
Under the 4-degrees scenario, high temperatures, which would occur once every 100 years in the absence of global warming, will occur 99 times in the same period, or almost annually.
Heavy rainfall at the once-in-100-years level would occur 5.3 times in the same period.
The annual amount of snowfall would tend to decrease, but the snowfall during extreme snowstorms may increase, according to the report.
The impact will also be felt in the seas.
Under the 4-degrees scenario, the coastal sea level will rise approximately 68 centimeters by the end of the 21st century, and sea ice in the Sea of Okhotsk in March will decrease by approximately 78 percent.
The oxygen concentration in seawater is also expected to continue to decrease until the end of the 21st century, and there are concerns that the habitats of sea creatures will be adversely affected, the report said.