What are the unresolved questions and future challenges for Palaeoclimate research?
I feel that one of the joys of science is that we are striving to push the boundaries of knowledge or clarifying our knowledge, I think curiosity is a strong personality trait in scientists, I think we have a drive to find out why. So, it was of little surprise that a Union Master Class on the unknowns of Palaeoclimate attracted approximately 200 people during the Wednesday afternoon session.
As someone who works on uncertainty in Pliocene climate models, I was keen to discover what two experts in palaeoclimate, Andre Berger and Wolfram Berger, thought of as the key questions to be covered.
I guess I should start by justifying palaeoclimate science. I mean, why would we want to look at the past? What can we gain from looking back? Surely we should only look forward and investigate the future, the now and the next, and prepare for what climate change will cause to happen. One of the founders of modern geology, James Hutton said “The present is the key to the past”, by which he meant you could look at present day processes and use them to work out what had formed the rocks we could see. Palaeoclimate is the inverse of his principle, that we use the past as the key to the present and the future. Like Hutton, however, we have unconformities in Palaeoclimate, and as sections of the rock record are missing, so we are missing some understanding from our studies, the gaps in our knowledge record, and this Union Master Class, was looking at where these are. This is crucial, because as Wolfram put it “The present is unusual”, and despite our extensive high resolution dataset of recent times, we can not see anything in this dataset which can intrinsically explain what is happening and why.
Andre opened quite rightly by pointing out that Palaeoclimate is a diverse field and that you should “never trust a model if not confirmed by data” and I agree 100% with him. The data works to show the model where it is doing well and where it is weak, the data can constrain uncertainty in model predictions and is vital for that. But, the relationship is symbiotic, modellers can turn to the data community and ask them, push them and encourage them to develop data for areas, where we lack it at present. Sometimes this challenges the data community to develop new analytical techniques, or leads to new drilling expeditions from teams on Antarctica or at sea as part of the IODP. Palaeoclimate modellers and palaeo-data people are a team, a community and it is important for development of our branch of climate science.
So, what are the unanswered questions? The presentations focussed mainly on the challenges in the last 3 million years and the last million specifically, the list below is from their talks, so they covered:
• The drivers of inter glacial, so what terminates the glacial time period and the role of both solar and greenhouse gases as forcings in this.
• The role of carbon dioxide in the Plio-Pleistocene transition
• The mid-Pleistocene transition from the 41kyr orbital cycle to the 100kyr orbital cycle.
• Climate sensitivity in models, the role of a number of feedbacks such as ice
• Carbon dioxide as a forcing AND as a feedback
• Sea level rises and rates of change.
So why are these unknowns important? They are important because we need to develop our understanding, but specifically they are crucial to our development. Geologically as Wolfram discussed, CO2 has been a feedback in the system, but humans have made it into a forcing as well as a feedback, separating the anthropogenic and the natural signal (modelled in the last IPCC report) is important showing the effect that our emissions have had on creating the ‘Hockey Stick’ graph. It is also linked to understand the onset of Northern Hemisphere Glaciation at the Plio-Pleistocene boundary, how did the change in CO2 lead to this new climate state? Likewise improving our understanding of the onset of inter-glacial periods is crucial in a whole number of elements of the climate and the earth system, we need to have a better understanding of post glacial ice melt and sea level rise, ~40% of the world’s population live within 100km’s of the coast to what level are they exposed to when sea level rise and when? It will also aid our understanding of a warming world, of which we live in today.
Personally, I also think we should look to the challenges of modelling the warmer climate optimums of the recent past, in time periods such as the mid-Pliocene Warm Period, the mid-Miocene Climatic Optimum, and rapid change events such as the Palaeocene-Eocene Thermal Maximum.
Warmer climates are a model test-bed and while I have a bias to this (as a Pliocene climate modeller), I think it is easy to understand why they are important. Warmer climates enable us to test how a model behaves in a warmer set of conditions, where the model is good and where it is weak at reproducing the climate. This has the potential to affect our ability to work with regional impacts of climate change. However, warmer climates are not without their complications. Workers in this field often have to state the caveat that we usually work in the equilibrium periods of the climate system, the world was warm for a stable period before a climate shift, this is different to our transient change we are experiencing. However we must continue in this area for it is the best record of warmer elevated CO2 world’s, we just don’t have the ability to test the models for these conditions without the use of palaeoclimate scenarios which provide data to validate our simulations.
These uncertainties are all vital to our understanding of the climate system, and without improving our understanding, how are we to fully understand what will happen as a result of climate change? And more importantly to those involved in planning and mitigation, where will it happen?
Palaeoclimate research has tackled a number of significant issues over the years, and developed ever increasing strategies for developing our knowledge. The Integrated Ocean Drilling Program (IODP) each year drills more and more cores of the ocean bed, allowing the data community to develop new and ever more detailed datasets. The modellers use this data, their models and their own understanding to push the models harder than ever to develop better simulations on a whole host of platforms, we have grown and developed, we are continuing to do so and we must continue, we can never stop, we can never ‘wait and see’ because that is not an option as Wolfram pointed out at the conclusion of his session.
I would like to thank the organisers of the EGU General Assembly for organising this session and I hope that they will encourage other sections to organise similar events at EGU2012, because I have left today’s session feeling stimulated to continuing pushing myself, to push my model and to push my colleagues into tackling our uncertainties, our unknowns, because only if we do that will we tackle what we don’t know!