The 100 kyr cycle
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The 100 Kyr cycle. Agnes Barszcz. Who wants to be a climatologist?. 2 teams: The Aphelions The Perihelions Rules Joker. What I am going to talk about. Various hypotheses for 100 kyr cycle Why Milankovich is wrong Suggest a new hypothesis See if it is reasonable

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The 100 Kyr cycle

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The 100 kyr cycle

The 100 Kyr cycle

Agnes Barszcz


Who wants to be a climatologist

Who wants to be a climatologist?

  • 2 teams:

    • The Aphelions

    • The Perihelions

  • Rules

  • Joker


What i am going to talk about

What I am going to talk about

  • Various hypotheses for 100 kyr cycle

  • Why Milankovich is wrong

  • Suggest a new hypothesis

  • See if it is reasonable

  • Look at it’s sensitivity to different parameters

  • Its flaws

  • What is the right theory

  • FUN: Giving out the price!!!


What is the 100 kyr cycle

What is the 100 kyr cycle?


What is causing it

What is causing it?

  • Many hypothesies:

    • The milankovitch cycle

    • Isostatic adjustmets of the litosphere under the weight of the glacier

    • Feedback between atmosphere ocean and Co2

    • …..

    • WE ARE STILL MISSING A SOLUTION!


Question 1

Question 1:

  • Who can tell me in less then 2 minutes what the Milankovich theory is ?


Milankovich and and why it is wrong

Milankovich and and why it is wrong!

  • 3 components

    • Eccentricity

    • Precession

    • Axial tilt


Which one was key for us

Which one was key for us?


Milankovich and and why it is wrong1

Milankovich and and why it is wrong!

  • 3 components: Eccentricity would be the one we are interested in!

    -> Top five reasons that we should NOT……


The 100 kyr cycle

  • Eccentricity changes are small

  • Orbital calculation when caried out with greater presision show a major cycle of 400 Kyr

Spectrum of 100-kyr glacial cycle: Orbital inclination,not eccentricity. By RICHARD A. MULLER* AND GORDON J. MACDONALD

http://www.pnas.org/cgi/reprint/94/16/8329.pdf , 1995

  • Well dated climate proxies show a 100 kyr cycle only over the last million of years

  • Double peak in frequency domain

  • Causality problem


Suggested solution

Suggested solution:

  • Changes in the orbital inclination


Find a suitable solution

Find a suitable solution…


Methods

Methods

  • Use simple or complex models


Pros and cons

Pros and cons

  • Complex models: Global circulation models

    • Pro: They take into account many parameters. They are more realistic

    • Cons: Require large computers $$$$$

    • -> Used to simulate equilibrium responses to various initial conditions


Pros and cons1

Pros and cons

  • Simple models:

    • Pro: Require less computer power, and run faster..

    • Con: Yield less realistic results. We do not see the influence of all the small parameters that we have neglected


What was used

What was used

  • A simple model


Claim

Claim

  • Hezi Gildor and Eli triperman say the 100 kyr cycle is NOT related to the milankovich cycle!!!!!!!!


The answer

The answer!

  • Their hypothesis is:

    • The variation of the ice-albedo between glacial and interglacial periods

    • Variant of the precipitation-temperature feedback


What the autors used

What the autors used

  • A simple zonaly averaged box


The components of the model

The components of the model

  • Ocean meridional thermohaline circulation

  • Atmospheric temperature-humidity feedback

  • Land glaciers

  • Sea ice


What where how

What,where,how?

  • The ocean model

    • 4 surface boxes (400 m)

      • 2 polar:

        • Water may be covered with sea ice of variable extent

        • Land may be covered with land ice of variable extent

      • 2 midlatitude boxes

    • 4 Deep water boxes (4000 m)

    • ** Important to note that the ablation rate of glacier stays constant with time….


What where how1

What,where,how?

  • The atmosphere model:

    • Each box can have 4 types of lower surfaces:

      • Land

      • Ocean

      • Land Ice

      • Sea ice

      • -> All have different albedos


The technicalities

The technicalities

  • What is a leapfrog scheme?


Leapfrog

Leapfrog


Why leapfrog

Why leapfrog?

  • Time reversible

  • Assures energy conservation

  • A better accuracy

    http://www.lifelong-learners.com/pde/SYL/s2node4.php

    http://einstein.drexel.edu/courses/CompPhys/Integrators/leapfrog/


How it goes

How it goes…

The crux of the problem


How it goes1

How it goes:

Ocean is ice free

  • Temperatures are mild

  • More precip then melting and carving

    ->->Land ice sheet grows


How does that affect the temperature

How does that affect the temperature?


As ice sheet grows slowly

As ice sheet grows slowly

  • The albedo of the earth decrease

  • The sea temperature are below zero only in the polar boxes.

    ->->-> At year 90 kyr, the global SST reaches zero degrees


What s special about the moment that the sst reaches zero

What’s special about the moment that the SST reaches zero?


Ice sheet rapidly grows

Ice sheet rapidly grows

  • As the SST attained a critical value, sea ice grows very rapidly!

  • In 20 year all polar box is covered in sea ice.

    ->->-> Sea ice switch is ON


When the switch is on

When the switch is on..

  • Sea Ice Stop growing!!!

    Why????


Self limitation of sea ice

Self-limitation of sea ice

  • The sea cools by giving out heat to the atmosphere

  • When it is covered by ice, there is no more exchange

  • The warm midlatitude waters mix with the polar waters

    ->->-> No more sea ice growth


The ice age

The ice age!

  • The glacier is at it’s maximum

  • The atmosphere is at it’s coldest

    How do we get out of an ice age??


Moisture feedback

Moisture feedback

  • There is less moisture captured by cold air, so less northward moisture transport

  • Because of the ice cap, there is also less evaporation in the polar region

    ->->-> Less moisture present in polar regions


We are loosing the icesheet

We are loosing the icesheet

  • The precipitaion rate is reduced by ½

  • The ablation rate stays constant

    ->->-> The glaciers retract


On the road to warm times

On the road to warm times

  • As the ice sheet retract, the albedo is decreasing.

  • Atmospheric and ocean temperatures rise slowly.

  • As long as there are ice sheets in polar region the ocean temperature in the region in below zero :sea ice is present.

    -> How does that affect the land ice sheet?


Further down on the road to warm times

Further down, on the road to warm times..

  • As long as the ice sheet is there, the land glaciers retreat fast

  • The sea ice, does melt by sloooowly…

    • The meltdown is slow because the SSt is close to zero..

      -> What is causing it to melt anyways?


Close to interglaciation

Close to interglaciation..

  • The sea ice melts down because of the heat advected and diffused by the ocean, that is coming from the midlatitudes.

    ->What will cause the abrupt acceleration of the melt down of sea ice?


Deep ocean

Deep Ocean

  • Because the deep ocean heats up:

    But Why?


The deep ocean

The deep ocean

  • Because of the melt down of the land ice sheet

  • The switch is OFF


Switch is off

Switch is “off”

  • All the ice melts down in about 40 years

  • Atmosphere and ocean temperatures rise again


And back

And back…

  • The temperatures are maximum

  • The ice sheet is minimum

  • The amount of precipitation is at it’s maximum

    ->We are back at the starting point!


The results

The Results

  • Simulated years from 170 kyr to 70 kyr


Theoretically it makes sense

Theoretically it makes sense…

Ok so we have a scheme…

Does it practically?


So what about the thc

So what about the THC?!?

  • THC = Thermohaline circulation

  • It was included in the model

  • It is rather an effect the a cause of the 100 kyr cycle

    What changes the strength of the THC?


The thc strength

The THC strength

  • When glaciers melt, there is a lot of fresh water relised: minimal THC (12Sv)

  • At interglacial periods, there is a lot of evaporation: Salier water: strong THC(16Sv)

  • When glaciers form: less evaporation: weaker THC(13Sv)


Is it an ok resolution to have only 4 boxes

Is it an ok resolution to have only 4 boxes?

  • How many did we use in the model we made in class??

  • It is only the upper part of the ocean that has to cool significantly for glaciation. (The lower part’s role is to provide delayed responses to various forcing)

  • It was already demonstrated in previous papers that this can be achieved in only a few tens of years


Does it make sense to have a 100 kyr period

Does it make sense to have a 100 kyr period?

  • Let’s do some simple math!!!!!

  • Volume of land glaciers:

    V= V max –V min

    =2.4 e16 m3

  • M-Accumulation rate

    maximum = 0.09 e6 m3/s

    minumum = 0.03 e6 m3/s

  • S-Ablation rate


Sensitivity to different parameters

Sensitivity to different parameters


Land ice sink term

Land–Ice sink term

  • Reduce by 4 %

    • Reaches faster the critical value at which the ice starts growing

    • Slower deglaciation

      -> Cycle is longer by 10 kyr

      -> Less saw-tooth like shape


Land ice sink term1

Land–Ice sink term

  • Increase by 20 %

    • Sink term always exceeds the precipitation rate

      ->>Glacier disappears!!!


Albedo

Albedo

  • Increase both land ice and sea ice albedo

    What will happen??


Albedo1

Albedo

  • Increase both albedos

    • Shorter cycle

    • Less land ice needed to reduce SST under the threshold value

    • Glaciers need to become smaller then before to enable a temperature increase that results in ice melting

      -> Shorter growth/Longer meltdown

      ->Shorter but more symmetric cycle


Albedo2

Albedo

  • Very significant increase in sea ice albedo

    -> Permanent sea ice cover

    ->No land Ice


Albedo3

Albedo

  • Very significant decrease in Sea ice albedo

    -> Makes the sea-ice mechanism less effective as a switch


Albedo4

Albedo

  • Increase in Land-ice albedo

    ->Reduces the amplitude of the oscillation and shortens the time scale

  • Converse is true


Emissivity

Emissivity

  • The long wave emissivity represents:

    • Cloud cover

    • Humidity

    • Land cover

    • Topography

    • Aerosols

    • CO2

      How will the emissivity evolve between a glacial minimum and maximum?


Emissivity1

Emissivity

  • The emissivity will increase between a glacial minimum and a glacial maximum because there is a smaller water vapor concentration


How about the co2

How about the CO2?

  • Pelletier and Marshall:

    • P’=0.015*ln( CO2 / CO2 ref)

  • So for a 30% CO2 change

    • P changes by - 0.003

  • Induces an increase in the time scale of the oscillation of about 9 kyr.

    -> Why longer?


How about the co21

How about the CO2?

  • Why longer?

    • Whole system is warmer,

    • We will need larger glaciers to turn the switch on!!


How about co2

How about CO2?

  • If we change P by +0.003

    • Cycle is longer by 12 kyr

  • If we change P by + 0.005

    • Cools the climate enough so there is a permanent sea-ice cover


Ice sheet thickness

Ice sheet thickness?


Ice sheet thickness1

Ice sheet thickness

  • Doesn’t change the cliamte!

    • Ice sheet play there role by

      • the albedo

      • Insulating properties


Freezing temperature

Freezing temperature

  • Similar effect as with the emissivity

  • Lowering the freezing T by 0.5o

    • Time scale is longer by 20 kyr

  • Increasing the freezing T by 0.5o

    • Time scale is shorter by 20 kyr


Problems

Problems

  • The model is

    • Quite simple

    • Highly idealized

    • Neglecting any zonal variations

    • Limited set of feed-backs


Problems1

Problems….

  • It is not synchronous with observations

  • Fails to predict the synchronous deglaciation of the southern hemisphere

    BUT


Take home message

Take home message

  • The aim of a such a simple model is NOT to be accurate with observations but just to explore potentially IMPORTANT effects and feedback of the climate.


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