





I have gone back to Japan in summer from the US for the first time in about 5 years. Before I flew to Japan, I really did not want to go back because it was summer and I knew the weather would be miserable. It’s incredibly hot and humid in summer in Japan. I spent summers in Indonesia and India and it seems like the Japanese summer in becoming just as hot as those two countries.

This year returning to Japan I sweated a lot just being outside. I don’t remember summers being quite so hot when I was younger. With the media broadcasting about global warming, I wondered if Japan is truly becoming hotter as compared to 20 or 40 years ago.

I looked up the statistics of temperatures in Japan and made some figures below. Japan Meteorological Agency has temperature records as old as 1898. It’s amazing that the records in some prefectures are older than that.

Annual mean temperature in Japan has been increasing with the pace of 1.19 degree Celsius per 100 years. Significantly high temperatures have been experienced in Japan since the 1990s.

The first figure below shows the mean temperature anomaly in Japan.









According to Japan Meteorological Agency, there are mainly two reasons why the agency shows the temperature anomaly, not temperature itself, so as to estimate the temperature overall in Japan. The first reason is that it’s extremely difficult to get an accurate temperature data from every place in Japan. For example, high mountains in northern or eastern parts of Japan can have about 3 degree Celsius in April while southern islands like Okinawa can have over 20 degree Celsius for the same period. Average temperatures for Japan nationwide would vary with where the observation points are. An accurate reading of the temperature in Japan maybe possible if there was some way to install thermometers in every location throughout the country. This is not a possible reality with current technologies.

The second reason is that measuring temperature itself does not meet the purpose of monitoring the climate. It is not necessary to know the temperature itself but important to understand if the temperature goes up or not over time in order to monitor the climate change. Therefore, they record the statistics of temperature anomaly, which is the deviation of mean temperature. In the figure, the base period for the mean temperature is from 1981 to 2010. The Japan Meteorological Agency chose 15 places to record the statistics in order not to have biased data and urbanization effect on the temperature.

You can see that the temperature in Japan has been increasing in the figure above. What I felt in Japan was probably correct, Japan is getting hotter and hotter over time !

I made the figures of temperature change for prefectural capital cities because the most of Japanese population live in cities and many people in the cities should be experiencing similar feelings to what I felt in summer in Japan. Due to the urban heat island effect, all of the cities that I checked their temperature show the increasing trend of temperature.







Sapporo

Aomori

Akita

Sendai

Yamagata

Fukushima

Niigata

Mito

Ustunomiya

Chiba

Tokyo

Saitama

Maebashi

Yokohama

Nagoya

Osaka

Kyoto

Nara

Hiroshima

Tottori

Takamatsu

Kochi

Fukuoka

Nagasaki

Kagoshima

Naha





