Research press release


Nature Communications

Planetary science: Earth's oceans lost in space



今回、Max Poppたちは、全体を水に覆われた理想化された惑星上で大気中の二酸化炭素濃度が変化した場合の影響をモデル化して、この変化が地球の気候システムに及ぼす影響可能性を調べた。Poppたちは、一連の数値シミュレーションが用いることで、二酸化炭素濃度が1,520 ppmに達すると、平均地表面温度が330 K(摂氏約57度)を超えることを明らかにした。そして雲のフィードバック効果によって地球の気候が不安定化して、上層大気の水蒸気量が増え、水蒸気量の少ない現在の地球の上層大気の場合よりも急速に大気中の水分が宇宙に流出すると考えられることが分かった。


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.

doi: 10.1038/ncomms10627

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