Increasing levels of carbon dioxide (CO2) have the potential to destroy the habitability of Earth-like planets, according to a study published in Nature Communications this week. This finding indicates that greenhouse gases can be just as effective as solar luminosity at burning away Earth’s vital water resources.
Over the course of millions of years, the luminosity of the Sun will increase, showering the Earth with more and more solar radiation. As a result, Earth’s surface temperature will increase to a point when liquid water will become unstable, and the oceans, rivers and lakes will evaporate into the atmosphere and eventually be lost to space, rendering the planet uninhabitable. However, whether a large increase in atmospheric concentrations of greenhouse gases, such as CO2, could also destroy the habitability of water-rich planets has so far remained unclear.
Max Popp and colleagues model the effect of changing CO2 levels on an idealised planet, which is entirely covered by water, in order to gain insight into the effect these changes may have on Earth’s climate system. Using a series of numerical simulations, the authors show that, once CO2 levels reach 1,520 parts per million, average surface temperatures are forced to exceed 330 K (~57°C). Cloud feedback effects destabilise the planet’s climate, bringing about moist conditions in the upper atmosphere, where water may be lost to space much faster than could occur in the drier upper atmosphere on Earth today.
Although the findings suggest that greenhouse gases can pose an equal threat to a planet’s habitability as does the Sun’s luminosity, this is a process that will occur at CO2 levels significantly higher than those experienced today, and over geological (millions of years) rather than human timescales.