A series of phenomena such as early flowering of plants and early migratory birds are suggesting that the traditional four seasons may have changed. A recent research study, “Changing Lengths of the Four Seasons by Global Warming� focuses on how the four seasons changed during 1952–2011 and will change by the end of this century in the warming Northern Hemisphere mid-latitudes. The study finds that the four seasons have changed and the changes will be amplified in the future. In the 59 years studied, the length of summer increased from 78 to 95 days and that of spring, autumn and winter decreased from 124 to 115, 87 to 82, and 76 to 73 days, respectively. In addition, summer is projected to last nearly half a year, but winter less than two months by 2100. Such changes can trigger a chain of reactions in agriculture, policy-making for agricultural management, and disaster prevention that require adjustment accordingly. The changing seasonal clock signifies disturbed agriculture seasons and rhythm of species activities, more frequent heat waves, storms and wildfires, amounting to increased risks to humanity. The seasonal-related topics involving ecology, the ocean, and the atmosphere also need to be revisited. This research letter was first published February 19, 2021: agupubs.onlinelibrary.wiley.com; doi.org/10.1029/2020GL091753; agu.org.