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Climate models in (palaeo-) climatic research. How can we use climate models as tools for hypothesis testing in (palaeo-) climatic research and how can we apply this to understand climate change from the Cretaceous to the near future? Nanne Weber. Temperature 1900-2100. +0.6C.

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Climate models in palaeo climatic research l.jpg

Climate models in (palaeo-) climatic research

How can we use climate models as tools for hypothesis testing in (palaeo-) climatic research and how can we apply this to understand climate change from the Cretaceous to the near future?

Nanne Weber


Temperature 1900 2100 l.jpg
Temperature 1900-2100

+0.6C

Different scenario’s for GreenHouse (GH) Gases


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History of climate

cold warm

last 300 Myr

last 50 kyr

last 1000yr

last 3 Myr


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Outline of this talk

  • What is a climate model?

  • Middle Holocene (6000 years Before Present =6 kyr BP): stable climate with warm NH summers

  • The Last Glacial Maximum (LGM, 21 kyr BP): cold, low GH Gas levels and large continental caps

  • The Paleocene-Eocene Thermal Maximum (PETM, 55 Myr BP): warm and high GH Gas levels



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  • Computations are done on

  • a grid with finite size

  • You have to choose a grid

  • Grid size is always limited

  • Small systems are not simulated, so have to be parameterised

  • Small ~ grid distance

  • Model can only be validated at large spatial scale


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Climate models tend to be very sensitive to these processes!!


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Completeness of model: this is determined by availability, computer resources and research question


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Climate models computer resources and research question

Model= a set of mathematical equations which are solved on a grid by a computer

*Equations describe many different processes (e.g. incoming radiation, cloud formation, heat transport, snow melt) in one or more components (e.g. atmosphere, ocean, vegetation) of the climate system

*With a given spatial resolution

*With given boundary conditions

(e.g. glacial ice sheets, Greenhouse

gases for 2100, Cretaceous land-sea

mask)


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The middle computer resources and research question

Holocene

(6 kyr BP)

Northern Africa wet

southern Europe and India also wet, northern Europe dry


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Het midden Holoceen computer resources and research question

Middle Holocene


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The middle computer resources and research question

Holocene

(6 kyr BP)

Hypothesis: changes in precipitation (and vegetation) at 6 ka due to orbital forcing

This holds also for cyclic patterns in sedimentary records


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Orbital parameters: computer resources and research questionmain cycles


Orbital parameters at 6kyr bp higher nh summer insolation l.jpg

Orbital parameters at 6kyr BP: computer resources and research questionhigher NH summer insolation

Changes in monthly-mean insolation as a function of latitude


The middle holocene changes in summer temperature and precipitation 6k minus 0k l.jpg

The middle Holocene computer resources and research questionchanges in summer temperatureand precipitation(6k minus 0k)


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Monsoon precipitation over Africa at 6 kyr BP: computer resources and research question1) models underestimate the signal as indicated by biomes2) vegetation and ocean feedbacks help!

Figure from IPCC Third Assessment Report (2001)


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The middle computer resources and research question

Holocene

(6 ka BP)

Hypothesis: changes in precipitation (and vegetation) at 6 ka due to orbital forcing

OK???


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The Last Glacial Maximum computer resources and research question

LGM versus

Pre-Industrial (PI) climate:

lower GH-gasconcentrations

LGM



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Hypothesis: NH continental ice sheetschanges in annual temperatureand precipitation(21k minus 0k)are due to low GH-gas and ice sheets


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Regional cooling NH continental ice sheets


Cooling over the north atlantic data diamonds and 16 different models l.jpg

Cooling over the north Atlantic: NH continental ice sheetsdata (diamonds) and 16 different models

Figure from Kageyama et al. (2006)


Hypothesis ok yes for regional mean cooling but we do not yet understand spatial details l.jpg

Hypothesis OK? NH continental ice sheetsYes for regional-mean cooling, but we do not (yet) understand spatial details


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If we do a transient run, with prescribed insolation (upper), CO2 (middle) and ice (lower), do we find a realistic Antarctic temperature?


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If we do a number of transient runs, each with separate forcings (insolation, CO2 and ice), where do we find a response to what?


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Different aspects of climate forced by different factors!! forcings (insolation, CO2 and ice), where do we find a response to what?

SAT – CO2, ice Monsoon – orbital


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What forces variations methane? forcings (insolation, CO2 and ice), where do we find a response to what?

One hypothesis is:

variations in the wetland source

Wetland area for today and LGM (Kaplan, 2002)


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Extended hypothesis: forcings (insolation, CO2 and ice), where do we find a response to what? in the cold and dry LGM climate wetland area is reduced and emissions are much lower than today


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Methane model: forcings (insolation, CO2 and ice), where do we find a response to what? compute wetland area and emissions from climatic fields (temperature, bottom moisture, etc)

black: NH high-latitudes

green: tropics

yellow: SH high-latitudes


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PETM: extremely warm, because of high GH-gas concentrations? forcings (insolation, CO2 and ice), where do we find a response to what?

Zachos et al. (2001)

Large ‘mismatch’ in temperaturebetween model (red line) and data (dots: red=PETM, yellow=just before or after PETM)

Fig. from Sluijs (2006)


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PETM simulation with EC-Earth, forcings (insolation, CO2 and ice), where do we find a response to what? with CO2=1400 ppm and prescribed sea surface temperatures. Results for DJF surface temps


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EC-Earth runs: forcings (insolation, CO2 and ice), where do we find a response to what?

polar warmth seems to be due to combination of feedbacks (sea-ice and snow, clouds,..)

Comparison of simulated temps with data (green dots)


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Ten forcings (insolation, CO2 and ice), where do we find a response to what?

Can one step twice into the same river?


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