Over the last 10,000 years, climate change has been shaped by changes in vegetation.

Follow the pollen trail. According to findings from a climate scientist at Washington University in St. Louis, records from historical plant life indicate the true tale of world temperatures.

According to new model simulations published in Science Advances on April 15, rising temperatures brought plants—and then even warmer temperatures.

Alexander Thompson, a postdoctoral research associate in earth and planetary sciences at Arts & Sciences, altered simulations from a prominent climate model to reflect the importance of altering vegetation as a main driver of global temperatures during the last 10,000 years.

Thompson had long been concerned about a flaw in models of Earth’s atmospheric temperatures dating back to the last ice age. Too many of these scenarios indicate consistent warming throughout time.

However, climatic proxy data reveals a different narrative. Much of this data points to a significant peak in global temperatures between 6,000 and 9,000 years ago.

Thompson suspected that the models were ignoring the role of changes in vegetation in favor of the effects of atmospheric carbon dioxide concentrations or ice cover.

“Pollen records suggest a large expansion of vegetation during that time, But previous models only show a limited amount of vegetation growth. So, even though some of these other simulations have included dynamic vegetation, it wasn’t nearly enough of a vegetation shift to account for what the pollen records suggest.”

Thompson said.

“Pollen records indicate a significant growth of vegetation during that time,” Thompson explained.

However, past models show just a limited quantity of vegetation development, “he explained. So, despite the fact that some of these other simulations contained dynamic vegetation, there wasn’t nearly enough of a vegetation shift to account for what the pollen records show.

In reality, there were considerable changes in vegetative cover.

The Sahara Desert in Africa was greener than it is today early in the Holocene, the current geological age. Other northern hemisphere vegetation thrived as well, including coniferous and deciduous forests in the mid-latitudes and the Arctic.

Thompson used pollen records to create a series of experiments using the Community Earth System Model (CESM), one of the most highly rated models in a large class of such models. He used simulations to account for a variety of previously unconsidered changes in vegetation.

“During the Holocene, expanded flora warmed the planet by up to 1.5 degrees Fahrenheit,” Thompson added. “Our new simulations are very similar to paleoclimate proxies. So it’s great that we can point to Northern Hemisphere vegetation as one possible contributor to resolving the contentious Holocene temperature dilemma. “

Understanding the amount and timing of temperature change during the Holocene is critical because it is a geologically recent epoch. Because the emergence of human agriculture and civilization happened during this time period, many scientists and historians from all disciplines are interested in understanding how the early and mid-Holocene climates varied from today’s.

As a graduate student at the University of Michigan, Thompson carried out this research. He is continuing his studies at Washington University in the laboratory of climate scientist Bronwen Konecky.

“Overall, our work underlines the need for accounting for vegetation change,” Thompson said. “Projections for future climate change are more likely to yield more reliable predictions if vegetation changes are included.”

Machine learning aids in the identification of climate thresholds that shape the distribution of natural vegetation. Alexander J. Thompson, The Northern Hemisphere’s vegetation change causes a Holocene heat peak, Scientific achievements (2022). The image was provided by Washington University in St. Louis.

Changes in global temperatures caused by vegetation during the last 10,000 years (2022, April 15), extracted on April 15, 2022, from

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