Early earth may have been more vulnerable to catastrophic deep freezes than previously thought, a new study has revealed.
University of Colorado Boulder researchers adapted a three-dimensional, general circulation model of Earth’s climate to a time some 2.8 billion years ago when the sun”s output was only 70 to 80 percent of that today but the geologic evidence indicates that the climate was as warm or warmer than now.
According to Eric Wolf, the new 3-D model of the Archean Eon on Earth that lasted from about 3.8 billion years to 2.5 billion years ago, incorporates interactions between the atmosphere, ocean, land, ice and hydrological cycles.
“The inclusion of dynamic sea ice makes it harder to keep the early Earth warm in our 3-D model,” Wolf said.
“Stable, global mean temperatures below 55 degrees Fahrenheit are not possible, as the system will slowly succumb to expanding sea ice and cooling temperatures. As sea ice expands, the planet surface becomes highly reflective and less solar energy is absorbed, temperatures cool, and sea ice continues to expand.”
Wolf and CU-Boulder Professor Brian Toon are continuing to search for the heating mechanism that apparently kept Earth warm and habitable back then, as evidenced by liquid oceans and primordial life forms.
While their calculations show an atmosphere containing 6 percent carbon dioxide could have done the trick by keeping the mean temperatures at 57 degrees F, geological evidence from ancient soils on early Earth indicate such high concentrations of CO2 were not present at the time.
The CU-Boulder researchers are now looking at cloud composition and formation, the hydrological cycle, movements of continental masses over time and heat transport through Earth”s system as other possible modes of keeping early Earth warm enough for liquid water to exist.
In the new 3-D model, preventing a planet-wide glaciation requires about three times more CO2 than predicted by the 1-D models, Wolf asserted.
For all warm climate scenarios generated by the 3-D model, Earth’s mean temperature about 2.8 billion years ago was 5 to 10 degrees F warmer than the 1-D model, given the same abundance of greenhouse gases.
“Nonetheless, the 3-D model indicates a roughly 55 degrees F mean temperature was still low enough to trigger a slide by early Earth into a runaway glacial event, causing what some scientists call a ‘Snowball Earth,’” Wolf added.