On March 14, 2021, the start of cherry blossom blooming was officially declared in Tokyo, and it was the same day as last year and the earliest date on record. It is said that the coldness of winter and the warmth of spring are related to the flowering of cherry blossoms. This year, the dormancy of cherry blossoms nationwide was broken early due to the strong cold air that caused record heavy snowfall from the end of last year to the beginning of January.

For Japanese people, plant changes such as the blooming of cherry blossoms serve as barometer to feel a sense of the four seasons. But how does climate change affect the four seasons? According to a paper published in Geophysical Research Letters, the four seasons in the Northern Hemisphere occurred in a predictable and even pattern each year. However, climate change is causing significant deviations to the length and start dates of each season. The paper warns that by 2100, inadequate climate change measures could lead to extremely long summers and short winters in the Northern Hemisphere, which could have a significant impact on agriculture, people's health and the environment.

The authors of the paper analyzed how future four seasons will shift based on climate models, using data on changes in the length and start date of the four seasons in the Northern Hemisphere from 1952 to 2011. Analysis showed that between 1952 and 2011, summer increased from 78 days to 95 days whereas winter decreased from 76 days to 73 days, spring decreased from 124 to 115 days, as well as autumn from 87 to 82 days. As a result, spring and summer starter earlier and autumn and winter started later. The Mediterranean region and the Tibetan plains in particular have experienced significant four-season cycle fluctuations. The authors predicted that if these trends continued without climate change mitigation efforts, winter would shrink to two months by 2100, spring and autumn would be shorter, while summer would be significantly longer.

The authors also asserted that shifts in seasons may affect animals and plants that are sensitive to temperature changes. Changes in the biological cycle can disrupt ecological conditions and lead to mismatches between animals and food sources. The impact on agriculture is particularly large, and warm, unseasonable days and snowfall can damage crop germination. Seasonal changes also pose problems for human health, such as extended exposure to allergic pollen and the northward movement of mosquitoes that carry the disease. In addition, there are concerns that seasonal shifts can lead to extreme meteorological events such as heat waves, wildfires, and cold waves recently observed in Texas.

When it comes to agriculture, it is necessary to strengthen resilience to seasonal changes. JIRCAS  is pursuing research to enhance basic knowledge for rice growing in accordance with seasonal changes, the timing and season of flower bud formation that determines early and late flowering varieties, and the mechanism of flowering and fertilization of rice. These studies may contribute to varietal improvements that speed up the flowering time of rice in order to avoid sterility due to the intense heat of summer.

Reference

Jiamin Wang et al, Changing Lengths of the Four Seasons by Global Warming, Geophysical Research Letters (2021). DOI: 10.1029/2020GL091753

Contributor: IIYAMA Miyuki (Research Strategy Office)