1. Evolution of the Asian monsoon from the Cretaceous to the modern – a modelling study. Dan Lunt, Alex Farnsworth, Claire Loptson, Paul Markwick
“How has palaeogeography, greenhouse gases, solar output, and evolving ice, controlled the Asian monsoon system over the last 150 million years ?”

2. Data from Friedrich et al (2012)
(1) Introduction
Last 150 Ma:
Major climate trends, + variability + ‘events’
Data from Friedrich et al (2012)

3. (2) Previous modelling work
Previous work on a limited number of time periods (mostly focussed on the role of Tibetan uplift)
Previously coarse (mostly idealised) palaeogeographies.
Models have improved since early work.
Hahn and Manabe, JAS, 1975
Zhisheng et al, Nature, 2001
Park et al, J.Clim, 2012

4. (3) Experimental Design
Palaeogeographies provided by Getech and Paul Markwick
Created using similar techniques to those outlined in Markwick (2007), based on published lithologic, tectonic and fossil studies, the lithologic databases of the Paleogeographic Atlas Project (University of Chicago), and deep sea (DSDP/ODP) data. Extensively updated from Markwick (2007), e.g. bathymetry, new rotations, more underlying data.

5. (3) Experimental Design
CO2 forcing
Solar forcing

6. (3) Experimental Design
The model: HadCM3L (with vegetation)
“state-of-the-art” [for long simulations]

7. (3) Experimental Design
The model: HadCM3L
How good is it for the palaeo?
Lunt et al, Clim. Past (2012)
Data compiled by Tom Dunkley Jones.

8. Baratropic stremfunction
(3) Experimental Design (consistent across all simulations)
Phase 1
Phase 2
Phase 3
Phase 4
50-years
400-years
57-years
years
Deep ocean temperature
Pre-industrial CO2
Pre-industrial SSTs
Paleogeography's
Uniform Veg
4xCO2
TRIFFID
Solar constants
Ozone concentrations
Lakes
No Ice + 2 x CO2
Creation of islands
Baratropic stremfunction
Ice + 2 x CO2
Ice + 4 x CO2
Simulation spinup – from Alex Farnsworth

9. (4) Results
Global means...

10. (4) Results
SSTs...
e.g.
Maximum warmth shifts from W. Pacific to E. Indian ocean in Late Eocene.
Zonal mean relatively constant.
ENSO is a constant feature.
Winter Arctic and Southern Ocean seaice for all time periods.

11. (4) Results Precipitation... e.g. ITCZ is constant feature
High precipitation does not penetrate into East Asian continent until later Cenozoic

12. (4) Results Vegetation... e.g.
Expansive N and S American deserts in early Cretaceous.
‘Green’ Sahara develops in late Eocene.
Maximum East Asian desert extent in Late Cretaceous

13. (4) Results Precipitation trends... Global EAMR – “roving”
“Fixed”(red) and “roving” (blue) East Asian monsoon regions (EAMR):
Precipitation trends...
Global
EAMR – “roving”
EAMR – “fixed”

14. (4) Results
Seasonality...
Cretaceous
Paleogene
Neogene

15. (4) Results Model-data comparisons...
Data trends are given here over the
Duration of the period (length of line):
Red = Trend disagreement
Black = Trend agreement

16. Summary Global precipitation decrease over the last 150 million years.
East Asian monsoon regions shows a decrease in the Cretaceous followed by increase in the Paleogene and early Neogene, then a decrease in the Pliocene.
Associated vegetation shifts, such as maximum desert extent in the late Cretaceous.
Shifts in seasonality, with maximum precipitation moving progressively earlier in the year.
Some support for some trends from data.

17. (5) Future work More data
Mechanistic understanding of modelled monsoon trends
Role of orbital forcing
Separate factors (paleogeography vs. CO2 vs. ice vs. solar)
Model internal parameter sensitivity studies.
CESM simulations of the Cretaceous (Chris Poulsen and Clay Tabour)
PMIP working group on ‘pre-Pliocene climates’
Joint venture between data and modelling communities
Model output available.