Earth Is Barely "Habitable," Say Scientists. Could Have Fooled Us - Evolution News & Views

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Earth Is Barely "Habitable," Say Scientists. Could Have Fooled Us


Reporting in the Astrophysical Journal, researchers at Penn State and the University of Washington have redefined the limits of the habitable zone around stars, placing it further out -- and, in so doing, setting Earth at the inner-most edge of our own solar system's habitable zone ("Habitable Zones Around Main-Sequence Stars: New Estimates"). Could that be right? Earth seems pretty hospitable to life.

According to the new model, the water loss (inner HZ) and maximum greenhouse (outer HZ) limits for our Solar System are at 0.99 AU and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 K and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water loss limits for stars with T_{eff} ~< 5000 K which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.
Translation? Interestingly, the new model doesn't take into account the role of cloud feedback on climate. That's the same issue that has confounded global warming catastrophists.

As a general rule, if your view of the climate (or the habitable zone) excludes Earth and its recent history, you can be pretty sure that you're mistaken.

Image: Earth at Night, NASA Earth Observatory/NOAA/DOD.