Researchers are claiming that plant growth has been in a sharp decline worldwide over the last two decades as a result of a lack of water vapor in the atmosphere, following a study.
Wenping Yuan of Sun Yat-sen University in Zhuhai, China, studied four global climate datasets along with colleagues and they've come up with the determination that there has been a 59 percent growth drop in vegetated areas globally and that's directly attributed to a vapor pressure deficit that has increased over more than 53 percent in vegetated locations since the late 90s.
Vapor pressure deficit is the difference between the pressure that would be given off by water vapor when the atmosphere is fully saturated and the pressure it actually gives off. When the deficit goes up, the pores on leaves close up and that leads to lower photosynthesis rates as the openings promote the exchange of gases.
According to Yuan, the complex workings of climate change is likely to blame for this. The wind speeds across oceans have slowed, in turn decreasing the vapor that reaches land. Also, as the planet gets warmer, the deficit gets bigger as the upper limit on the water vapor the atmosphere can hold goes up when temperatures on the land increase.
The research team analyzed satellite photos and found a corresponding decrease in global vegetation and leaf coverage growth rates. Said rates had increased between 1982 and 1998 but they've since dropped.
The width of tree rings was also observed. The method is used to determine how old a tree is and, after 1998, there's been a decrease in average width at more than 100 of the 171 sites worldwide.
The team predicts that vapor pressure deficit will continue to go up in the coming decades.
“This atmospheric drought will last into the end of this century,” Yuan says.