What Was Earth Like Last Time At 400 ppm? It Was The Pliocene, And It Was Very, Very Different

[hatrack]

What was the climate and sea level like at times in Earth's history when carbon dioxide in the atmosphere was at 400ppm?

The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around four million years ago during a geological period known as the Pliocene Era (between 5.3 million and 2.6 million years ago). The world was about 3 degrees Celsius warmer and sea levels were higher than today.

We know how much carbon dioxide the atmosphere contained in the past by studying ice cores from Greenland and Antarctica. As compacted snow gradually changes to ice, it traps air in bubbles that contain samples of the atmosphere at the time. We can sample ice cores to reconstruct past concentrations of carbon dioxide, but this record only takes us back about a million years.

Beyond a million years, we don't have any direct measurements of the composition of ancient atmospheres, but we can use several methods to estimate past levels of carbon dioxide. One method uses the relationship between plant pores, known as stomata, that regulate gas exchange in and out of the plant. The density of these stomata is related to atmospheric carbon dioxide, and fossil plants are a good indicator of concentrations in the past.

Another technique is to examine sediment cores from the ocean floor. The sediments build up year after year as the bodies and shells of dead plankton and other organisms rain down on the seafloor. We can use isotopes (chemically identical atoms that differ only in atomic weight) of boron taken from the shells of the dead plankton to reconstruct changes in the acidity of seawater. From this we can work out the level of carbon dioxide in the ocean. The data from four-million-year-old sediments suggest that carbon dioxide was at 400ppm back then.

EDIT

https://www.stuff.co.nz/environment/climate-news/122064928/climate-explained-what-the-world-was-like-the-last-time-carbon-dioxide-levels-were-at-400ppm

[bronxiteforever]

1. K&R. No humans were around then just

Australopithecus. No good news here.