EGU 2014

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 ?”

EGU 2014Data from Friedrich et al (2012)

(1) Introduction

Last 150 Ma:

Major climate trends, + variability + ‘events’

EGU 2014

(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

EGU 2014

(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.

EGU 2014

(3) Experimental Design

Solar forcing

CO2 forcing

EGU 2014

(3) Experimental Design

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

EGU 2014

(3) Experimental DesignThe model: HadCM3L

How good is it for the palaeo?

Lunt et al, Clim. Past (2012)Data compiled by Tom Dunkley Jones.

EGU 2014

Phase 1 Phase 2 Phase 3 Phase 4D

eep

ocea

n te

mpe

ratu

re

50-years 400-years 57-years 500-1000 years

Pre-industrial CO2

Pre-industrial SSTsPaleogeography'sUniform Veg

Lakes4xCO2

TRIFFIDSolar constantsOzone concentrations

Creation of islandsBaratropic

stremfunction

No Ice + 2 x CO2

Ice + 2 x CO2

Ice + 4 x CO2

(3) Experimental Design (consistent across all simulations)

Simulation spinup – from Alex Farnsworth

EGU 2014

(4) Results

Global means...

EGU 2014

(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.

EGU 2014

(4) Results

Precipitation...

e.g.

ITCZ is constant feature

High precipitation does not penetrate into East Asian continent until later Cenozoic

EGU 2014

(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

EGU 2014

Precipitation trends...

Global

EAMR – “roving” EAMR – “fixed”

“Fixed”(red) and “roving” (blue) East Asian monsoon regions (EAMR):

(4) Results

EGU 2014

Cretaceous

Paleogene

Neogene

(4) ResultsSeasonality...

EGU 2014

(4) ResultsModel-data comparisons...

Data trends are given here over theDuration of the period (length of line):Red = Trend disagreementBlack = Trend agreement

EGU 2014

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.

EGU 2014

(5) Future work

More data

Mechanistic understanding of modelled monsoon trends

Role of orbital forcing

Separate factors (paleogeography vs. CO2 vs. ice vs. solar)

Role of orbital forcing

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.Email: d.j.lunt@bristol.ac.uk