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 ?”

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

(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

(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.

(3) Experimental Design CO2 forcing Solar forcing

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

(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.

Baratropic stremfunction (3) Experimental Design (consistent across all simulations) Phase 1 Phase 2 Phase 3 Phase 4 50-years 400-years 57-years 500-1000 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

(4) Results Global means...

(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.

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

(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

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

(4) Results Seasonality... Cretaceous Paleogene Neogene

(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

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.

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