Changing Vegetation a Key Driver of Global Temperatures Over Last 10,000 Years

Aerial Forest Stream

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

Follow the pollen. Records from past plant life tell the real story of global temperatures, according to research from a climate scientist at Washington University in St. Louis.

Warmer temperatures brought plants — and then came even warmer temperatures, according to new model simulations published in Science Advances.

Alexander Thompson, an Arts & Sciences postdoctoral research associate in earth and planetary sciences, revised simulations from an influential climate model to represent the significance of changing vegetation as a key driver of global temperatures during the last 10,000 years.

Thompson had long been troubled by a problem with models of Earth’s atmospheric temperatures since the last ice age. Too many of these simulations showed temperatures warming consistently over time.

However, climate proxy records tell a different story. Many of those sources indicate a marked peak in global temperatures that occurred between 6,000 and 9,000 years ago.

Aerial Forest

According to new model simulations, warmer temperatures brought plants, and then came even warmer temperatures.

Thompson had a hunch that the models could be overlooking the role of changes in vegetation in favor of impacts from atmospheric carbon dioxide concentrations or ice cover.

“Pollen records suggest a large expansion of vegetation during that time,” Thompson said.

“But previous models only show a limited amount of vegetation growth,” he said. “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.”

In reality, the changes to vegetative cover were significant.

Early in the Holocene, the current geological epoch, the Sahara Desert in Africa grew greener than today — it was more of a grassland. Other Northern Hemisphere vegetation including the coniferous and deciduous forests in the mid-latitudes and the Arctic also thrived.

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-regarded models in a wide-ranging class of such models. He ran simulations to account for a range of changes in vegetation that had not been previously considered.

Alexander Thompson

“Projections for future climate change are more likely to produce more trustworthy predictions if they include changes in vegetation.” — Alexander Thompson

“Expanded vegetation during the Holocene warmed the globe by as much as 1.5 degrees Fahrenheit,” Thompson said. “Our new simulations align closely with paleoclimate proxies. So this is exciting that we can point to Northern Hemisphere vegetation as one potential factor that allows us to resolve the controversial Holocene temperature conundrum.”

Understanding the scale and timing of temperature change throughout the Holocene is important because it is a period of recent history, geologically speaking. The rise of human agriculture and civilization occurred during this time, so many scientists and historians from different disciplines are interested in understanding how early and mid-Holocene climates differed from the present day.

Thompson conducted this research work as a graduate student at the University of Michigan. He is continuing his research in the laboratory of climate scientist Bronwen Konecky at Washington University.

“Overall, our study emphasizes that accounting for vegetation change is critical,” Thompson said. “Projections for future climate change are more likely to produce more trustworthy predictions if they include changes in vegetation.”

Reference: “Northern Hemisphere vegetation change drives a Holocene thermal maximum” by Alexander J. Thompson, Jiang Zhu, Christopher J. Poulsen, Jessica E. Tierney and Christopher B. Skinner, 15 April 2022, Science Advances.
DOI: 10.1126/sciadv.abj6535

6 Comments on "Changing Vegetation a Key Driver of Global Temperatures Over Last 10,000 Years"

  1. Ok let’s take a closer look at this first of all in the first quarter of each century we are that much closer to the sun because we are in an elliptical orbit in the last quarter of the century we are further away take for instance when I was a kid we watched the news and Irv Weinstein came on channel four buffalo channel and said this is the blizzard of 76 and it snowed so bad for day they had to call out the army to help clear the streets hell they even have out t shirts for this and soon as we move into the next quarter of century we will get a little colder the reason not as much snow is because we are drinking all the water that mother nature supplies us look at caves of limestone that have collapsed on them self because those aqua filters are now empty from the time it rains or snows it takes as long as six months for it to seep thru rock sagravel and sand this is just another ploy to get you to buy more but get less but it’s now new and approved stuff they sell us and yes much damage has resulted from this but it will subside like the tide washes in and away

    • Clyde Spencer | April 17, 2022 at 3:54 pm | Reply

      In order to have any scientific hypothesis taken seriously, one has to have their easily-checked-facts correct. Right out of the gate, you state something that is incorrect. Earth does NOT take a century to transit its elliptical orbit. It does so every year, being closest to the sun during the southern hemisphere Summer. Look up the definition of “orbit.” Also, instead of taking two ‘facts’ from the TV and connecting the unconnected dots, try reading from a reputable source: https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/

      It is obvious that you don’t know anymore about caves than you do astronomy. Why don’t you sign up for a geology class and learn a little bit about the world that exists beyond TV and the internet.

    • Clyde Spencer | April 17, 2022 at 4:50 pm | Reply

      Is “moron” your nom de plume, or were you addressing one of the two of us? A single word without context or explanation doesn’t tell readers anything about your IQ or even working vocabulary — although it does give us a hint.

  2. Clyde Spencer | April 17, 2022 at 4:37 pm | Reply

    While I’m sympathetic to the idea of looking for alternative climate influences other than the simplistic — “We don’t know what else could be causing warming, so it must be CO2!” — approach, I’m concerned about the simplistic approach of using visible-light albedo.

    First off, reflectance spectra of vegetation varies considerably, with the only commonality being having high reflectance in green light and even higher in near-infrared, and strong absorption in red and blue light. There is also a small specular component that approaches the spectrum of the sun for glancing angles, and is usually missed by relying on albedo rather than total reflectance. Reflectance also varies strongly by season. Furthermore, it appears that these researchers didn’t consider the impact of warming oceans on photosynthetic life in the oceans.

    It is a good start, but needs refinement. One of my most serious concerns is the poor skill models seem to have with regard to reproducing historical temperatures without tuning of the parameterized variables. If the day comes that it can truly be said that the models are just physics and math, then I will have more trust in them. This research may help accomplish that goal.

  3. Ralph Gardner | April 18, 2022 at 11:52 am | Reply

    The fact that we have been in a geological ice age called the Quaternary Glaciation for 2.588 million years in a warm period that happens about every 100,000 as the Earth’s changes from a 90,000 year colder slight ellipse to a warmer near circle for around 10,000 years under the influence of Jupiter and other planets.

    We have 4.5 million people dying of the effects of the cold we are still in that increases heart attacks and strokes around 25% while about 0.5 million are dying from the effects of heat according to a large international study.

    It is so cold that almost half of our energy production goes to heating. It is so cold that cars and houses come with heating standard and air conditioning optional.

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