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you

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[Music]

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hey I'm Jade this is my first talk and

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today I'd like to talk to you about the

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possibility of snowball bifurcations on

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tightly locked exoplanet so orbiting and

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stars okay so as everyone in the room

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here knows by now we found many ago

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planets and much of the fields focus is

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on trying to figure out which one's of

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those could be habitable now to know

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that we need to know which ones can

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support surface liquid water because

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habitability is a surface property okay

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now a major factor that can affect a

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planet's habitability is the ice albedo

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feedback so here on the left is very

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simple cartoon illustrates the effect so

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we know that the ocean absorbs much more

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solar radiation than ice which is very

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reflective so if we were to increase the

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insulation on the planet we would have a

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melting of sea ice which will decrease

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the albedo and induce more melting but

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if we were to lower the inspiration we

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would have some sea ice on forming which

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will increase the albedo and induce more

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freezing so because of this

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non-linearity a planet like the earth

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can have two stable States for a range

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of installations so we can look here at

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the plot on the right here the vertical

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axis is the sign of the ice latitude so

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the ice latitude is the latitudinal

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extent of ice on the planet and the

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horizontal axis is the insulation the

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solid lines represent stable States and

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the dashed line unstable sticks so if we

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start at the top right with a planet

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like the earth like modern earth in its

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warm state and we decrease the

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insulation eventually it will jump into

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a snowball state right there now to get

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out of this noble state we would need to

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increase the insulation but much more

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than the glaciation insulation so a

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planet might have a hard time to escape

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that snuggle state and this could have

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bad implications for habitability but at

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the same time although I'm not an expert

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on this for Earth

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like going through a snowball stage has

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been associated with the rise in oxygen

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and in complex life so it could be a

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good thing but still up for debate so

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okay now on this beautiful figure again

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by funny we see that the boundaries of

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the habitable zone strongly depend on

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the stellar type so for an M dwarf here

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which is much smaller and dimmer than a

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G sorry the habitable zone is much more

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close in so in fact it's so close in

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that a planet that's orbiting in the

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habitable zone of those M stars are

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close enough to likely become tightly

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locked as we see here so this means that

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one side of the planet will always be

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facing the star and the other side will

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always be facing away so because those

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planets orbit their stars in such a

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different manner than rapidly rotating

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planets like the earth we want to know

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whether they could still go through a

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snowboard bifurcation like we know the

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earth can now there's already been some

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work done on the subject first let's

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look here at those two plots by Joshi in

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2012 the top panel shows that the peak

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of the third spectrum of an M star is

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that a higher wavelength than that of a

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G star and because of this the Eifel

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video of a planet orbiting those M stars

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will be much lower so the non-linearity

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of the Eifel video effect will be

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reduced and we can imagine that a planet

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orbiting an M sir might have a more

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difficult time going through a snowball

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bifurcation because of that and also

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more recently here shields in 2014

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showed that for an M star compared to a

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G star the range of information at which

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there is by stability is much smaller so

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again the planet might have a more

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difficult time going through its network

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bifurcation now both of those works were

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about comparing the different solar

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spectra of an M star energy star and

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seeing how going like orbiting an M star

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might make it more difficult for the

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planet to go through the bifurcation but

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what we want to know is whether or not

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the fact itself that the planet

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My Luck whether it's orbiting an M star

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or a G star or whatever could make it

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more difficult to go through the

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bifurcation okay so we use a global

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climate model called blessing so it's a

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3d GCM of medium complexity we set it up

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in a modern earth continual

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configuration computed clouds and kept

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this here to fix a 360 ppm and here's

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what we see first for the earth so I'm

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here the top panels the surface

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temperature the bottom the sea ice cover

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and again the horizontal axis is always

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insulation the red stars here correspond

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to a warm start so where the planet is

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completely ice-free and the blue stars

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correspond to a cold start or it's

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completely ice covered on both of those

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initially and we see that we retrieve

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the expected snowboard bifurcation here

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and we have by stability so great the

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GPM reproduces the very well-known

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result for the earth but now using it in

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a tightly locked configuration we see

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something quite different right here on

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the left so whether we start cold or

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warm the surface temperature increases

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or decreases linearly with the

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insulation we don't see a snowboard

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bifurcation now you might be wondering

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about the small gap right here in

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surface temperature for those

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intermediate ranges of installations but

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this is not real hysteresis it's

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actually just a model artifact due to

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the simple CI scheme of the GPM we're

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using I don't want to get more into it

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now but if you'd like to know you can

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always ask me later but what's really

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important is just setting up the planet

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in the GCM in a tightly locked

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configuration gets rid of the snowboard

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by vacation and this is with a GSR

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spectrum all right so we can imagine

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that if we had used an answer spectrum

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it would be even less likely to go

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through a bifurcation okay now how can

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we understand this well we can use a

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simple energy balance model right here

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where the absorb solar radiation is

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equal to the outgoing long-wave plus the

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heat transport both on parametrize so

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first for the earth here's an example

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state for the planet and what's

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important to note right here is so this

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is the equator in the middle

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it's that the installation shape is

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flatter on the equator right we don't

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see a super sharp increase in insulation

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from the pole to the equator now solving

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this IBM for the ice latitude so again

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the isolated is the latitudinal extent

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of the ice on the planet we retrieve the

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bifurcation diagram that I showed and

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explained at the beginning so where the

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planet can jump into a snowball stage

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here okay now setting up the EVM in a

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tightly locked configuration what's

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important is that the insulation

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increases really sharply from the

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Terminator which is here to the sub-zero

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point which is here right compared to

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the earth which was much more flat now

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solving the EBM again for the ice

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latitude the bifurcation diagram here

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shows no bifurcation so it looks like

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the EBM is able to explain what's

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happening in our GCM now I just note

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that we are able to retrieve the

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bifurcation in this slightly large

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configuration in our ABM if we just

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greatly increase the heat transport

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let's just keep this in mind for the

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next slide ok so this slide explain

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what's happening in DBM but before

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looking at it ultimately what you need

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to know is that whether or not the

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planet goes through on the bifurcation

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depends on the insulation shape so let's

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first look at on the right here for the

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case where the planet does go through

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the bifurcation so we have the ice line

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somewhere between the pole and equator

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and we perturb it slightly towards the

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equator now there the insulation and the

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hay transport will be greater but

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because as we saw for the earth the

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insulation ship is not so sharp or on

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the equator at that point the hay

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transport will actually have increased

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more than the insulation increased and

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because of this di slang we continue all

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the way to the equator for the planet is

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in a snowball state now on the left for

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the stable case for example for a

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tightly locked planet again we have a

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nice line somewhere between the

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Terminator and the substellar point and

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we again perturb it slightly so towards

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the sub-zero point this time but because

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as we saw for HIV locked a net the rise

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in insulation is so sharp from the term

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later to the substernal point this time

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the installation will have increased

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more than the heat transport and because

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of this the ice line will return to its

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original position so the planet doesn't

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go through a snowball bifurcation so

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this is my conclusion that tightly

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locked exoplanets are unlikely to go

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through a snowball bifurcation because

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of the sharp increase in insulation from

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the Terminator to the sub-zero point and

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we have a paper in prep on this that

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will be submitted soon if you're

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interested thank you hi my name is

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Richard Archer from University Colorado

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Boulder I thought it was really great

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presentation so congratulations I have a

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question regarding volcanism so in terms

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of snowball earth it was there are

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people that suggested that the release

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of some all births condition was driven

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by volcanic co2 so after it's still all

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earth you actually have very large

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greenhouse effect and I just wonder what

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you think that might apply to to your

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model so that's to get out of the snow

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board once you're already in it

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volcanoes could out gas a lot of co2

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right I mean we just saw that tightly

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locked planet don't go through the solar

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bifurcation but yes they can be in a

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snowboard state if you decrease the

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insulation enough however to get out of

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this noble state it would be much easier

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than for the earth because it's not a

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bifurcation so you would just need to

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oh so you mean for example if we had

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tried using the GCM with a much higher

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co2 level sure okay yeah I was just

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wondering the the result eeeh tightly

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locked exoplanets are unlikely to go

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through its Noble is that conditional on

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assuming that there is not any heat

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transport from the insulated side to the

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shadow side of a tidally locked planet

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ah no no there is heat transport so you

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have a basic model of default this is

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how much heat transport you have and

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then you still get tight and you just

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and you still get a what - you do not go

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through the bifurcation but if you

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increase that above what you expect then

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you do go through them the heat

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transport yes yes yeah you are actually

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yeah actually it's interesting that in

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the GCM I didn't present it in the talk

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but we found that the heat transport on

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the tightly locked planet is much

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greater than for the earth and it's

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great enough that on the IBM we should

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be able to get the bifurcation back but

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the difference in albedo it's smaller

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than for the earth because of so many

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clouds at the Sub Zero point and they

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still get the tidally locked planet to

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not go through the bifurcation so as

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heat transport is really important it's

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definitely happening and it's enough to

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normally go through a bifurcation if

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that albedo range wasn't smaller please

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any more questions if not we can give

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Jada round of applause thank you very