Large Herbivores Grazed On Grass Year-Round In The Arctic When CO2 Was 180 ppm. Now They Cannot.

A new study reports that during Pleistocene cold stages, when CO2 concentrations dipped below 200 ppm, Arctic Siberia had much more fertile soil and productive vegetation than exists today. Extensive grassland ecosystems could sustain year-round grazers: horses, mammoths, bison. Today this region’s large herbivores must be fed by humans to secure survival due to extremely cold, grassless winters.

As recently as 20,000 to 17,000 years ago, Pleistocene wild horses grazed on grass year-round in the Arctic (North Slope, Alaska).

Today, “horses need human assistance to overwinter in the far North because there is generally little they can eat, and what there is, is deeply buried by snow” (Guthrie and Stoker, 1990).

large herbivores grazed on grass year round in the arctic when co2 was 180 ppm now they cannot - Large Herbivores Grazed On Grass Year-Round In The Arctic When CO2 Was 180 ppm. Now They Cannot.

Image Source: Guthrie and Stoker, 1990

This was a period of time – a Pleistocene cold stage – when summer temperatures were actually “higher here than they are today” (Kuzmina et al., 2019) even though modern CO2 levels are over 400 ppm and Pleistocene cold stages had ~180 ppm CO2 levels.

large herbivores grazed on grass year round in the arctic when co2 was 180 ppm now they cannot 1 - Large Herbivores Grazed On Grass Year-Round In The Arctic When CO2 Was 180 ppm. Now They Cannot.

Image Source: Kuzmina et al., 2019

In Arctic Siberia, mammoths grazed on grass year-round on Wrangel Island (71°N) until just 3700 years ago. At that time the Siberian Arctic was warm enough and the soil fertile enough to sustain expansive grasslands. Now, due to a much colder climate, it cannot.


The grass available to sustain such large animals throughout summer and winter needed to have been quite substantial. A conservative estimate is that a small mammoth required 25 kg of grass per day to survive (Bryson et al., 2010). This is over 9 tonnes of grass per year, per animal.large herbivores grazed on grass year round in the arctic when co2 was 180 ppm now they cannot 2 - Large Herbivores Grazed On Grass Year-Round In The Arctic When CO2 Was 180 ppm. Now They Cannot.

Image Source: Bryson et al., 2010

A new study (Reinecke et al., 2021) further emphasizes the Pleistocene cold stage vegetation “must have consisted of open grassland” and that the productivity of the vegetation “should have been relatively high compared to current conditions to support high densities of large herbivores.”

Further, “soils should have been more fertile than today in the arctic” during these Pleistocene cold stages.

large herbivores grazed on grass year round in the arctic when co2 was 180 ppm now they cannot 3 - Large Herbivores Grazed On Grass Year-Round In The Arctic When CO2 Was 180 ppm. Now They Cannot.

Image Source: Reinecke et al., 2021

The study documents  recent attempts to reintroduce large grazers like horses and bison to the Siberian Arctic (called “rewilding”) at “Pleistocene Park,” founded in 1996. However, the fertile soils and extensive grassland vegetation during Pleistocene cold stages “are not easily restored” in today’s frigid climates and harsh winters. For example, today’s October to March temperatures average about -30 to -45°C in Verkhoyansk, a location described as “the most miserable place in the world” to live.

Horses and bison could survive on their own, grazing on grass throughout the year, during the apparently milder arctic winters of the Pleistocene cold stages. Today, however, the large herbivores at Pleistocene Park must be fed by humans in winter to survive. And the animals still “have difficulties surviving the harsh winters despite receiving additional fodder.”

It is interesting that we are told modern climate conditions in the Arctic are so warm (due to high CO2 concentrations) they are endangering the fauna that live there. It would appear the exact opposite is more likely true.

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