Follow the pollen. Records from previous plant life tell the true story of global temperatures, according to research by a climate scientist at the University of Washington in St. Louis.
Higher temperatures brought plants – and then came even warmer temperatures, according to new model simulations published April 15 in Advances in Science.
Alexander Thompson, a postdoctoral fellow in Earth & Planet Sciences in the Arts & Sciences, updated the simulations from an important climate model to reflect the role of vegetation change as a key driver of global temperatures over the last 10,000 years.
Thompson has long had a problem with models of Earth’s atmospheric temperatures since the last ice age. Too many of these simulations showed that temperatures rose steadily over time.
But climate mediation files tell a different story. Many of these sources indicate a remarkable peak in world temperatures that occurred between 6,000 and 9,000 years ago.
Thompson felt that the models could overlook the role of vegetation changes in favor of the effects of carbon dioxide concentrations on the atmosphere or ice cover.
“Pollen records suggest a large expansion of vegetation during this period,” Thompson said.
“But previous models show only a limited amount of vegetation,” he said. “So while some of these other simulations involved dynamic vegetation, the vegetation shift was hardly enough to explain what the pollen files suggested.”
In fact, the changes in vegetation cover were significant.
At the beginning of the Holocaust, in the present geological age, the Sahara Desert in Africa became greener than it is today — it was more of a meadow. Other vegetation in the northern hemisphere, including the coniferous and deciduous forests of mid-latitude and the Arctic, has also flourished.
Thompson took data from pollen records and designed a set of experiments with a climate model known as the Community Land System Model (CESM), one of the best models in a wide range of such models. He ran simulations to explain a series of vegetation changes that had not been considered before.
“The swollen vegetation during the Holocene warmed the globe to 1.5 degrees Fahrenheit,” Thompson said. “Our new simulations are closely aligned with the representatives of the old climate. Therefore, it is fascinating that we can point to the vegetation of the northern hemisphere as a possible factor that allows us to solve the controversial riddle of the Holocene temperature.”
Understanding the scale and timing of temperature changes during the Holocene is important because it is a period of recent history, geologically speaking. The rise of human agriculture and civilization occurred during this period, so many scientists and historians from different disciplines are interested in understanding how the climate of the Early and Middle Holocene differed from today.
Thompson did this research work as a graduate student at the University of Michigan. He continues his research in the laboratory of climatologist Bronwen Konecky at the University of Washington.
“Overall, our study emphasizes that accounting for vegetation change is critical,” said Thompson. “Forecasts for future climate change are more likely to produce more reliable forecasts if they include vegetation changes.”
Machine learning helps to identify the climatic boundaries that shape the distribution of natural vegetation. More info: Alexander J. Thompson Advances in Science (2022). DOI: 10.1126 / sciadv.abj6535. www.science.org/doi/10.1126/sciadv.abj6535 Provided by the University of Washington in St. Louis
Reference: Changes in vegetation have shaped global temperatures over the last 10,000 years (2022, April 15) Retrieved April 15, 2022 from
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