Vegetation change has been a key driver of global temperatures for the past 10,000 years, according to a study.
Higher temperatures led to the plants – and then came even higher temperatures, according to new model simulations published in the journal Science Advances.
According to Alexander Thompson, a research associate with a doctorate in terrestrial and planetary sciences at the University of Washington in St. Louis, pollen records can tell the true story of global temperatures.
Models of Earth’s atmospheric temperatures since the last ice age show that temperatures are constantly warming over time.
But Thompson noted that climate proxy records tell a different story. Many of these sources show a marked peak in global temperatures between 6,000 and 9,000 years ago.
He said the models could ignore the role of changes in vegetation in favor of the effects of atmospheric carbon dioxide or ice cover concentrations.
“Pollen records suggest a great expansion of vegetation during this time,” Thompson said.
“But previous models show only a limited amount of vegetation growth,” he said. “So, although some of these other simulations involve dynamic vegetation, it wasn’t nearly enough of a change in vegetation to account for what pollen records show.”
In fact, the changes in the vegetative cover were significant.
At the beginning of the Holocene – the current geological era – the Sahara Desert in Africa became greener than it is today, it was more of a pasture.
Other vegetation in the Northern Hemisphere, including coniferous and deciduous forests in the middle latitudes and the Arctic, is also thriving.
Thompson took evidence from pollen records and designed a set of experiments with a climate model known as the Community Earth System (CESM) model. He conducted simulations to account for a number of changes in vegetation that had not been considered before.
“Expanded vegetation during the Holocene warmed the globe by up to 1.5 degrees Fahrenheit,” Thompson said.
Understanding the scale and timing of temperature changes during the Holocene is important, as the rise of human agriculture and civilization occurred during this time.
“Overall, our study emphasizes that accounting for vegetation change is crucial,” Thompson said.
“Forecasts of future climate change are more likely to give more reliable forecasts if they include changes in vegetation.”
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