Have you ever heard your grandfather or grandmother say that, even in the middle of summer, it never used to be this hot? Let's look at the annual average temperature for Tokyo now compared to 100 years ago. In 2013 it was 17.1℃, while in 1913 it was 13.4℃, meaning the temperature has risen by more than 3℃ in the last century. The average temperature in August, the middle of summer, was 29.2°C in 2013 and 23.8°C in 1913. That's an increase of 5.4°C. Maybe you already suspected it, but when you see the numbers like this it is clear that the temperature in Japan is higher than it used to be.

It is not only in Japan, as the whole earth is experiencing rising temperatures. About 170 years ago, when Japan was first becoming a modern nation, the planet’s temperature gradually started to rise. This was a time when people's lives were mainly based on agriculture, but industrialization was on the rise and many people began to work in factories. Furthermore, we know that the temperature has been rising sharply since the 1950s, a time of reconstruction after war, when industry was flourishing, factories were multiplying, and many cars were on the road.

The earth is warm because it absorbs heat from the sun. While the planet absorbs this heat, at the same time it also releases excess heat into space. That's how the temperature balance is maintained. But this balance has been lost, and the earth’s temperature is gradually rising. We humans are the ones who have upset this balance.

episode 1
The Earth is Getting Warmer

[Detailed data and explanations 1]
Tokyo is Becoming Increasingly Hotter

Source: Japan Meteorological Agency Home Page
https://www.data.jma.go.jp/obd/stats/etrn/view/monthly_s3.php?prec_no=44&block_no=47662

The graph above, based on data from the Japan Meteorological Agency, shows the monthly and annual average temperatures in Tokyo for August over the past 150 years. The graph reveals the temperature has been gradually increasing over the past 150 years. We can see that the annual average temperature (orange graph) has been steadily increasing. The red graph for August also shows that the temperature has been increasing year by year.

[Detailed data and explanations 2]
Sweltering Days and Tropical Nights are Increasing

Source: Japan Meteorological Agency Home Page
https://www.data.jma.go.jp/cpdinfo/himr/csv/tmaxGE35/tmaxGE35_tk.csv
https://www.jma.go.jp/jma/kishou/books/hakusho/2016/csv/p102.csv

The graph above shows the number of sweltering days and tropical nights in Tokyo. To be considered as a “sweltering day” the maximum temperature needs to be above 35°C, and a "tropical night" is when the temperature goes no lower than 25°C between dusk and dawn. The data shows the number of extremely hot days and tropical nights has been increasing over the past 100 years.

[Detailed data and explanations 3]
The Global Average Temperature is also Rising.

Source: Japan Meteorological Agency
https://www.data.jma.go.jp/cpdinfo/ipcc/ar6/IPCC_AR6_WG1_SPM_JP_20210901.pdf

The above graph is taken from the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Look at the fluctuating black line in the right graph "b) Changes in global average temperature (annual average)". You can see that the rate of increase has been high since the 1950s. Based on multiple data sources, the IPCC report states the temperature rose by 0.85℃ between 1880 and 2012. The graph on the left, "a) Global Temperature (Decadal Average Change)," combines various data estimates of temperature from the year AD 1 with measured temperatures since 1850. It shows that over the long history of the world, the temperature of the earth has had an explosive increase in the last 100 years of modern industrialization.

＊About the IPCC
IPCC (Intergovernmental Panel on Climate Change) is an organization established under the United Nations in 1988. Scientists selected from around the world gather to organize the results of their research on global warming and publish a report every few years. Based on these reports, the international community will undertake measures to prevent global warming.