Column: Earth is on the path to resurrecting a climate not seen in 3 million years

·3 min read

Climate change skeptics frequently cite the 140-year record of global temperatures as too brief to prove that atmospheric carbon dioxide is a factor in defining climate. How about climate over the last 400 million years? When CO2 was high, as high as 3,000 ppm, the planet was 10–25 degrees Fahrenheit warmer than today, and there was no ice at either pole. The CO2 came from volcanoes. When the CO2 was very low, the planet was frozen over (called snowball earth); even the oceans had ice at the Equator. This long history makes it very clear that atmospheric carbon dioxide has played an important role in determining the climate for 400 million years.

Over the last 400 million years, the Earth was more often in its hothouse mode than its icebox mode. There were crocodiles in northern Canada, along with Dawn Redwoods. The land masses did not reposition through shifting of tectonic plates; they were in the north all along.

The Earth began to cool permanently when India crashed into Asia 40-50 million years ago. This collision formed the Himalayas and initiated a monsoon cycle. Rains in the mountains dissolved carbon dioxide and the mountain rocks absorbed the carbon dioxide, dropping the CO2 content gradually over millions of years from over 1,000 ppm into the range of 180-300 ppm. We humans have lived our 300,000 years existence with carbon dioxide levels between 180-300 ppm — until the beginning of the industrial era.

As the Earth was cooling it went through a period with atmospheric CO2 around 400-420 ppm. This was the Mid-Pliocene, 3 million years ago. The mean annual surface temperatures were approximately 2-4 degrees Celsius warmer than preindustrial temperatures. There was no ice at the North Pole (ice began forming on Antarctica around 32 million years ago) and a 50-foot increase in sea level. The sea level rise was large because temperature and ice were in equilibrium.

Today, the talk of limiting warming to 2 degrees Celsius is largely limited to lobbyists of oil and utility companies who want to say we’re fine and don’t need to act. Most scientists conclude a 2.5 to 4.6 degrees Celsius increase is very likely by 2100. Thus, we will have temperatures and climate close to the Mid-Pliocene. Sea level rise has not tracked temperature because it may take a century or three for the ice to melt. If we track the Mid-Pliocene, all the Arctic ice, most of Greenland ice, and some portion of Antarctic ice will melt. The USA will look very different. For example, the Florida Peninsula will be under water.

On our current “business as usual” path, it is entirely possible that the average temperature of Earth eventually rises from 58 to 68 degrees Fahrenheit . Our current course could bring about this outcome in 150-300 years. The 68 degree temperature is important because historically at that temperature, or higher, there has been no polar ice, and ocean levels have been 200 feet higher.

For further aspects on this topic, watch NOVA: Polar Extremes

Norm Holy is a resident of Bloomington.

This article originally appeared on The Herald-Times: Columnist urges action to reduce carbon, limit global warming