So conferences and marking students work has made me lazy with this blog it seems (bad excuse I know!). However I now have some time to spread the gospel..well i shouldn't say that as climate sceptics my jump on me saying that this is indeed a belief and not a science.

I thought I might try and showcase some recent work I have been doing on the South-east Asian monsoon system and how it has evolved over geologic time-scales. Most work continues (and rightly so) to focus on more short term variability in the Asian monsoon, in particular intraseasonal, interannual and more pressingly, interdecadal variability and how the structure, energetics and inertia of the monsoon system can be perturbed.

In paleoclimate one of the biggest questions we are trying to ask is what exactly is the role of changing carbon dioxide concentrations on the climate over the last 200 million years. In a global view we are quite certain about the role carbon dioxide plays on the large-scale climate system, being one of the key reasons from the transition from a 'hot-house' climate to a 'cold-house' climate during the Eocene to Oligocene. Carbon dioxide is however not always the fundamental driver of climate change not only on global scales (e.g. changed in ocean gateways have a large impact of the distribution of energy and momentum globally through changing circulatory features in the ocean and atmosphere) but more regional scales, such as the Asian monsoon system.

Monsoons are controlled by the relative heat capacities of the land sruface and ocean whereby the latter has a great heat capacity meaning it can store the incoming solar radiation for many months after the solar equator (where the sun is at its most incident) releasing the stored energy slowly over the months. Because the land-surface has a much smaller heat capacity compared to the oceans is heats up very fast, heating the atmosphere above it which becomes 'hotter' then the surrounding atmosphere over the oceans, creating a strong convective environment. This creates a strong temperature differential driving onshore advection of the moisture rich atmosphere over the oceans onto land where it is subsequently convective through the atmospheric column with a high lapse rate and where the moisture entrained in the air parcels are subsequently precipitated, causing the large rain storms which are associated with monsoons.

Now over geologic time scales there have been two competing theories which have governed the onset and evolution of the Asian monsoon system, primarily Carbon dioxide levels and the Himalayas-Tibetan Plateau oregon. Recent work has tended to focus on carbon dioxide being the driving factor for the onset of the monsoon (though theories vary greatly as to exactly when the onset has occurred due to patchy spatially poor proxy data) and it's evolution over time. However through modelling the various geologic stages with the use of supercomputers we can test which theory is more likely through a consistent model framework from the beginning of the Cretaceous to the modern day.

The figure above shows the current results showcasing how the monsoon has evolved and changed in the model (black which show annual precipitation and red lines which shows JJA precipitation in the top panel) for each geologic stage.  The proxy data points have also been input in the above in the top panel of the figure and the proxy-data trend in the bottom panel. The trend results provides the best for data-model comparisons as point source proxy data are highly locally dependent meaning they do not give accurate regional means which is what needs to be compared again the model regional monsoon region. The black lines in the data trend represent the quantitative proxy-data and red stippled lines the qualitative proxy-data trends. As you can see the trend data matches the model data very well in ost circumstances. Were the fit is less reliable analysis has found that this data representing a more localised signal and not a regional monsoon signal.
This work has been nearly the culmination of 2 and a half years work and finally coming to fruition.

I shall leave this here for now and in the comming days/week I shall continue the rest (of what I think at least!) is quite a fascinating story of trying to unlock history of the Asian monsoon system.

Alex