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Follow the pollen. Records of past plant life tell the true story of global temperatures, according to a study by a climatologist at the University of Washington in St. Louis.
Higher temperatures led to the plants – and then came even higher temperatures, according to new model simulations published on April 15 in Scientific achievements.
Alexander Thompson, a research associate with a doctorate in earth and planetary sciences in the arts and sciences, is updating simulations of an important climate model to reflect the role of changing vegetation as a key driver of global temperatures over the past 10,000 years.
Thompson has long been concerned about a problem with Earth’s atmospheric temperature patterns since the last ice age. Too many of these simulations show that temperatures heat up constantly over time.
But 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.
Thompson had a hunch that the models might 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 Model (CESM), one of the best respected models in a wide range of such models. 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. “Our new simulations are closely related to paleoclimatic proxies. So it’s exciting that we can point to the vegetation in the Northern Hemisphere as a potential factor that allows us to resolve the controversial Holocene temperature conundrum. “
Understanding the scale and timing of temperature changes throughout the Holocene is important, as this is a period of recent history, from a geological point of view. The rise of human agriculture and civilization occurred during this time, so many scholars and historians of various disciplines are interested in understanding how the climate of the early and middle Holocene differed from today’s.
Thompson conducted this research work as a graduate student at the University of Michigan. He continues his research in the laboratory of climatologist Bronwen Koneki at the University of Washington.
“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.”
Machine learning helps to identify the climatic thresholds that shape the distribution of natural vegetation. More information: Alexander J. Thompson, The change in vegetation in the Northern Hemisphere leads to a Holocene heat peak, Scientific achievements (2022). DOI: 10.1126 / sciadv.abj6535. www.science.org/doi/10.1126/sciadv.abj6535 Courtesy of Washington University, St. Louis
Citation: Changes in global temperatures formed by vegetation over the last 10,000 years (2022, April 15), extracted on April 15, 2022 from
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