Climate models in palaeo climatic research l.jpg
Sponsored Links
This presentation is the property of its rightful owner.
1 / 33

Climate models in (palaeo-) climatic research PowerPoint PPT Presentation


  • 65 Views
  • Uploaded on
  • Presentation posted in: General

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.

Download Presentation

Climate models in (palaeo-) climatic research

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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

Different scenario’s for GreenHouse (GH) Gases


History of climate

cold warm

last 300 Myr

last 50 kyr

last 1000yr

last 3 Myr


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


A climate model describes the Earth’s climate system


  • 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


  • Important processes that have to be parameterised:

  • Turbulent transport of heat, impuls, moisture

  • Clouds

  • Precipitation

  • Boundary layers

  • Radiation

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


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


Climate models

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)


The middle

Holocene

(6 kyr BP)

Northern Africa wet

southern Europe and India also wet, northern Europe dry


Het midden Holoceen

Middle Holocene


The middle

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


Orbital parameters: main cycles


Orbital parameters at 6kyr BP:higher NH summer insolation

Changes in monthly-mean insolation as a function of latitude


The middle Holocenechanges in summer temperatureand precipitation(6k minus 0k)


Monsoon precipitation over Africa at 6 kyr BP: 1) models underestimate the signal as indicated by biomes2) vegetation and ocean feedbacks help!

Figure from IPCC Third Assessment Report (2001)


The middle

Holocene

(6 ka BP)

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

OK???


The Last Glacial Maximum

LGM versus

Pre-Industrial (PI) climate:

lower GH-gasconcentrations

LGM


The Last Glacial Maximum (LGM) period of maximum extent of NH continental ice sheets


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


Regional cooling


Cooling over the north Atlantic: data (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


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


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


Different aspects of climate forced by different factors!!

SAT – CO2, ice Monsoon – orbital


What forces variations methane?

One hypothesis is:

variations in the wetland source

Wetland area for today and LGM (Kaplan, 2002)


Extended hypothesis:in the cold and dry LGM climate wetland area is reduced and emissions are much lower than today


Methane model: compute wetland area and emissions from climatic fields (temperature, bottom moisture, etc)

black: NH high-latitudes

green: tropics

yellow: SH high-latitudes


PETM: extremely warm, because of high GH-gas concentrations?

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)


PETM simulation with EC-Earth,with CO2=1400 ppm and prescribed sea surface temperatures. Results for DJF surface temps


EC-Earth runs:

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

Comparison of simulated temps with data (green dots)


Ten

Can one step twice into the same river?


  • Login