A reduced climate sensitivity!

Now that I have your attention, I should probably make clear that this post is not about the Earth. I’m just back from a meeting where one of the speakers was Ian Boutle, lead author of a paper in which they Explor[ed] the climate of Proxima B with the Met Office Unified Model (pre-print available here).

Proxima Centauri B is a recently discovered Earth-sized planet in an 11-day orbit around Proxima Centauri, the closest star to the Sun. There are a couple of aspects of this system that may influence the planet’s climate sensitivity. One is that the star is much cooler than the Sun, and so emits most of its radiation at longer wavelengths. The other is that the planet is probably tidally locked – its rotation period will match its orbital period so that one side always faces its host star.

What Boutle et als. model indicates is that the above factors appear to result in a climate sensitivity that is quite a bit lower than that of the Earth (about two-thirds). One reason is that the albedo of ice decreases with increasing wavelength. Since the host star to Proxima Centauri B emits mainly at longer wavelengths (compared to the Sun) the ice albedo feedback is significantly reduced. Also (and this is the bit I wasn’t quite clear on) the changes in cloud cover appear to mainly occur on the night side, and so have little impact on climate sensitivity. There also appears to be global-scale circulations that also suppress the temperature on the day side, due to the efficient cooling of the night side of the planet.

The above has some potentially interesting implications for habitability. To be clear, we don’t really know what is required for a planet to be habitable, or not, so – in this context – it simply refers to the possibility of there being liquid water on the surface. However, if Proxima Centauri does have a smaller climate sensitivity than the Earth, then this implies that it is less sensitive to changes in stellar flux and, hence, that there is a greater range of parameter space over which it could support liquid water on its surface.

Of course, this is all based on models, so we don’t know even if Proxima Centauri B actually has an atmosphere and, if it does, if it can actually support liquid water on its surface. However, future space missions (such as the James Webb Space Telescope) and future ground-based telescopes (such as the European Extremely Large Telescope) might be able to make observations that could tell us something about Proxima Centauri B’s atmosphere, so we may have some idea about this in the not too distant future.

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14 Responses to A reduced climate sensitivity!

  1. John Hartz says:

    If the climate sesnsitivity of the Earth is the “Holy Grail”, then what is the climate sensitivity of Proxima Centauri B? 🙂

    PS – The Devil made me do it.

  2. On a tidally locked planet, the climate sensitivity is the last of your worries. Poor life that had to evolve there (if it did).

  3. Proxima b is so close to Proxima that the stellar wind is about 2000 times what it is at Earth. It’s unlikely any planetary atmosphere could survive for billions of years in those conditions.

  4. Victor,
    Indeed 🙂

    That is an issue (this paper suggests that you might expect the planet’s magnetosphere to be smaller than the Earth’s). Another issue is that these low-mass stars are quite active and hence you might be regularly bathed in x-rays from stellar flares.

  5. Had a look at the paper, the tidally-locked case is as bad I had feared, either you get fried in the middle of the sun facing side, or you get blow away by extreme winds elsewhere.

    Respect that the UK MetOffice Unified Model is able to model such an extreme atmosphere without crashing.

  6. On the positive side, it should be quite save to contact a tidally locked planet. They will have no interest in Earth with its hostile climate: daily and seasonal cycle, with unpredictable weather, sun, wind, highs and lows. 😦

    They must have solved so many problems we did not yet solve.

  7. izen says:

    The habitable region is in the twilight zone ?

  8. angech says:

    If there are oceans the wind would not affect life in the sea so much, perhaps an aquatic zone.

  9. Andrew Dodds says:

    VV –

    Actually an interesting point; research on artificial Neural Networks of the sort thought to most closely resemble biological ones suggests that sleep is a critical part of the network-training process. You do wonder what cycle aliens on a tidally locked planet would use..

    I prefer looking for life around orange dwarf starts myself..

  10. Eli Rabett says:

    The guy to ask is Yuk Yung

  11. John Hartz says:

    Meanwhile, baclk on Planet Earth…

    Ice at Both Poles Shrinks to Record Lows by Sabrina Shankman, inside Climate News, Mar 22, 2017

  12. John Hartz says:

    Pop Quiz: Where will Judith Curry, John Christy, John Christy & Micheal Mann appear together next week?

    Hint: House panel to challenge climate science by Timothy Cama, The Hill, Mar 22, 2017

  13. jacksmith4tx says:

    Remember when climate skeptics used to get so indigent because switching to renewable energy would lead to severe energy poverty and the deaths of millions?
    Introducing Trump’s Make Climate Great Again:
    Americans have one of the largest carbon foot prints (16.1 tons/person) so Trumpcare will reduce carbon emissions by actually shortening the lifespan of the average lower and middle class American. CBO estimates that 24 million will be without health care within 10 years and that maybe conservative. If things work out as planned average US lifespan should drop to 65yrs which will solve the Social Security budget shortfall and eliminate the national debt.
    Wait there’s more!
    If Trump makes good on deporting the 11 million illegal immigrants that could
    mean we could hit our Paris climate targets too.

  14. russellseitz says:

    Cue usual suspects to write 20 Reasons Why Hafnium Carbide X-Ray Flare Geoengineering Won’t Work

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