Warm periods of the past

Schedule

• 14.00 Introductions
   
• 14.05-14.40 Gavin Foster (University of Southampton)
  Insights into our warm future from the Palaeocene-Eocene Thermal Maximum 
   
• 14.40-15.15 Erin McClymont (Durham University)
  Living in a 400 ppmv CO2 world - lessons we might learn from the Pliocene epoch
   
• 15.15-15.40 Tea
   
• 15.40-16.15 Emilie Capron (Niels Bohr Institute, Denmark) 
  Back to the future? Climate clues from the Last Interglacial 
   
• 16.15-16.50 Dan Lunt (University of Bristol)
  Climate and climate sensitivity from past warm periods - what do the models tell us?
   
• 16.50-17.30 Panel discussion about implications for future.

Background

Worlds that are warmer than today have a particular relevance for the 
future. Although no period in the past is exactly analogous to the 
climate of the future, they all hold lessons about the impacts of 
warmth, and provide test cases, outside their calibration range, for 
models.

The last interglacial, around 125,000 years ago, had particular warmth at 
the poles, and sea level considerably higher than today. It holds the 
advantage that it is relatively well-documented, allowing the climate 
dynamics affecting polar regions and ice sheets to be examined. The 
Pliocene, around 3 million years ago offers the most recent period where 
warmth is associated with CO2 levels comparable to those of today. Going 
back further (up to aroiund 50 million years ago) we reach more extreme 
warmth in conditions where Earth's geography was different to that of 
today. Our speakers will discuss their fascinating findings, built on 
novel geochemistry and Earth system modelling, about the causes and 
consequences of warmth in these periods.  We will finish with a panel 
discussion about how these results inform us about what to expect and 
what to avoid in the future.

Abstracts

Insights into our warm future from the Palaeocene-Eocene Thermal Maximum, Gavin Foster (University of Southampton)

Our relatively recent geological past contains numerous real-world examples of the Earth functioning in altered climate states.  Intervals of past global warmth hold the potential to provide unique insights into how the Earth System functions when significantly warmer than today and presents a reality check for the imperfect climate model simulations of our warm future.  In particular, observations of our geological past allows us to explore the “unknown unknowns” that are impossible to parameterise even in the most sophisticated climate or Earth system model. 

Here I will present new boron isotope data from the Palaeocene-Eocene Thermal Maximum (PETM) ~56 million years ago.  The PETM is an interval of global warmth commonly interpreted as being driven by the massive and rapid destabilization of carbon from surficial sedimentary reservoirs. If this interpretation is correct, this event has both important implications for the amplification of future fossil fuel emissions via carbon-climate feedbacks and offers a way to examine how climate sensitivity may vary as a function of background climate state.  

Living in a 400 ppmv CO2 world - lessons we might learn from the Pliocene epoch, Erin McClymont (Durham University) 

During the mid to late Pliocene (~3.5-2.7 Ma), global temperatures are estimated to be around 3°C warmer than modern, with comparable atmospheric CO2 concentrations to those we record today (~400 ppmv). The Pliocene thus represents an example of a climate state in long-term equilibrium with current and predicted near-future CO2 concentrations. Furthermore, we have precise knowledge of the orbital forcing of solar radiation, the continental configurations were close to modern, data can be temporally constrained through multiple stratigraphic frameworks, and many of the species extant today were also present. This combination of factors increases our confidence in understanding the climate signals recorded in the data, and in our ability to undertake data-model comparison to better understand mechanisms for change. In this presentation I will outline new research which has been targeting a better understanding of the mid- and high-latitude changes in climate using sequences of ocean sediment records. With a focus on mid- and high-latitude climate records, a better understanding of the interactions between ice sheets, sea ice extent, and ocean circulation can be generated. An over-arching message from all of these studies is that we see variability in Pliocene climate on glacial-interglacial and shorter timescales, which suggest that this interval of geological time was not simply a ‘warm, stable, climate’.

Back to the future? Climate clues from the Last Interglacial, Emilie Capron (Niels Bohr Institute, Denmark)  

During the last interglacial period (between 129 000 and 116 000 years ago), the climate of the Earth was warmer than during the preindustrial. In particular, deep ice cores suggest that it was at least 3 degree C warmer in Antarctica. But how warm was it in the rest of globe? How sensitive the Greenland and the Antarctic ice sheets were to this warming? And consequently what was the global sea level?

In the context of our warming planet, addressing these questions is particularly relevant and this will be the focus of my talk.

I will present recent insights based on paleoclimatic records on the Last Interglacial climate, sea level and the state of the Greenland and the Antarctic ice sheets. I will also show how Last Interglacial climatic reconstructions can provide valuable benchmarks against which to test and improve climate simulations performed for this time interval with models also used for future climate predictions.

Overall, my talk will illustrate how by studying the Last Interglacial, it is possible to gain insights into climate processes and feedbacks under a range of temperature changes comparable to projected future changes.

Climate and climate sensitivity from past warm periods - what do the models tell us? Dan Lunt (University of Bristol)

Models can be powerful tools to explore past climates, in particular when combined with geological data to evaluate and constrain the model predictions, or through using the models to better understand the data. In this talk I will discuss how models allow us to assess the relative contribution of palaeogeographic change, solar change, and carbon cycle change to climatic variations during warm climates of the last 150 million years.   The results have important implications for the interpretation of single-site palaeo proxy records. In particular, the results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change.  In addition, I will discuss the constancy (or otherwise) of climate sensitivity (the response of the system to a doubling of CO2) on these timescales, and the resulting relevance (or otherwise) for constraining future climate.