Researchers discover a slowdown in the Earth's stabilized nature calendar

Sometimes referred to as the Nature Calendar, phenology is relevant to the seasonal life cycle of plants and animals and is one of the key indicators of climate change. It is the observance of natural events like the first formation of buds and flowers in the spring and the changing colors of the leaves in the fall. According to researchers at the University of New Hampshire, phenology can do the same when the temperature of the Earth's air slows considerably.

In a study recently published in the journal Nature CommunicationsThe researchers focused on a 15-year period early in this century, when there was a temporary slowdown in rising air temperatures in the Earth. It continued to increase, but more slowly than in the years before and after. Scientists have discovered that during this period, phenology remained relatively constant from one year to the next, with no noticeable increase in the length of the growing season.

"This discovery was a big surprise for us as the Earth's climate changes and affects the length of the seasons," said Jingfeng Xiao, an associate professor of research at the UNH Earth Systems Research Center. "In recent decades, we have had longer growing seasons, with spring before and after autumn, but that was not the situation from 1998 to 2012 in the northern hemisphere."

Phenology plays a major role in the regulation of photosynthesis, transpiration and energy exchange of plants. When phenology stabilizes, it is easier to estimate when to start a garden, when fall foliage will reach its peak and facilitate life cycles such as pollination, migration, and mating. .

The researchers examined carbon dioxide exchanges between plants and the atmosphere from 56 sites in forests, cultivated lands, savannahs, shrublands and grasslands in the northern hemisphere. They were the first to compare these results with satellite images indicating the dates of foliage (when leaves appear in spring) and senescence (when leaves fall and plants die or fall dormant in autumn) to estimate duration and the timing of the growing season, which has remained pretty much the same for this period.

Earlier senescence and / or later senescence may mean a longer growing season, increased crop production and crop yield, as well as an increase in the amount of carbon dioxide absorbed by plants of the atmosphere. However, this can also mean the need for increased water use and could affect the flow of water courses and aggravate water crisis issues.

"It's not just plants, many people are physically affected by phenological trends," Xiao said. "Anyone with seasonal allergies knows that a spring or early growing season can mean an earlier allergy season."

Phenological variations also make it more difficult for scientists to estimate carbon, water and energy exchanges between the atmosphere and the Earth's surface, which can then affect climate change projections.

Scientists admit that the period of time they have studied, where the temperature of the Earth's air has slowed, may seem to contrast with other research on global warming, but they point out that even during this period, the Earth's temperatures continued to increase. They point out that temporary trends such as this require very long data sets – at least a decade or more – to properly assess overall phenological trends.