CliMathNet Conference 2016, University of Exeter

Keynote Speakers


Klaus Fraedrich, Max Planck Institute for Meteorology, Hamburg, Germany

Title: Experiments with an Earth-like climate: Abrupt, static, and transient changes

Experiments with an Earth-like climate are performed by inducing static, transient and abrupt changes in terms of a parameter variation of solar constant and atmospheric greenhouse gases. Focusing on static, dynamic, and memory hysteresis, a brief introduction to a new Intermediate Complexity AO-GCM (PLASIM-GENIE) is given before analyzing numerical experiments (PLASIM plus mixed layer ocean) under changing atmospheric radiative forcing jointly with the corresponding analytic results of a toy-model (EBM).
Static change experiments demonstrate that the solar constant varying by 20% reveals warm and snowball Earth regimes depending on the system’s history. Thermodynamic analysis shows (i) both climates being characterized by global mean surface temperature and entropy growing with increasing solar constant; (ii) the climate system’s efficiency decreases (increases) with increasing solar constant in present-day warm (snowball) climate conditions, and (iii) climate transitions near bifurcation points are characterized by high efficiency associated with the system’s large distance from the stable regime.
Abrupt change experiments are performed by greenhouse effects being switched off. (i) CO-2 concentration is abruptly decreased from its actual value. Assessing model response as a bifurcation point, the steady solution shows a critical CO-2 threshold with the model ending up in a snowball Earth state. The transition to ice-covered Earth is favored removing Q-flux corrections (of ocean heat transports). Zero- and one-dimensional EBMs substantiate the results. (ii) Ozone (O-3) is abruptly decreased from its actual value. Although ozone appears in the Earths atmosphere in a small abundance, it plays a key role in the energy balance of the planet through its involvement in radiative processes. The total removal of O-3 content in an Earth-like atmosphere leads to a new equilibrium suggesting the model to attain a colder state mainly because of the water vapor content decrease. Most of the cooling occurs in the Southern Hemisphere while in the northern ice cap melts consistently. This process is governed by northward cross-equatorial heat transports induced by general circulation change.
Transient change experiments demonstrate dynamic and memory hysteresis when changing the direct atmospheric radiative forcing associated with a well-mixed carbon dioxide (CO-2) concentration. Modifying the planetary thermodynamic state (surface temperature) the hysteresis is effected by different CO-2 change rates: (i) The response is due to infrared cooling (for constant temperature lapse-rate) which, in turn, is related to the surface temperature through the Stefan-Boltzmann law in a ratio proportional to the new infrared opacity. Subsequent indirect effects of water-vapor-greenhouse and ice-albedo feedbacks enhance the response. (ii) Different rates of CO-2 variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO-2. (iii) Far from bifurcation points the model’s climate depends on the history of the radiative forcing thus displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model determined by the ocean’s mixed-layer depth. These results are supported by a zero-dimensional energy balance model.


Rachel Kuske, University of British Columbia

Title: New averaging results motivated by climate models: fat tails, oscillations, and tipping.

Abstract: We review recent results where new averaging approaches are developed and applied in the context of systems with multiple time scales and fat tails  and in non-autonomous multiple scale systems with oscillatory forcing.  These types of systems appear in a variety of higher dimensional climate models, as well as in other areas of application.  The results open new research directions, with potential to better address questions like: which mechanisms contribute to fat-tail statistical properties appearing in climate data?  What are reasonable approximations for multiple scale systems with non-Gaussian behaviour?  How can these approximations provide insight into the dynamics of larger models, such as parameter ranges with large variability,  tipping, or reversibility?   Some areas for further research are discussed.


Xiaofeng Li, Newcastle University

Title: Explaining recent wetting and cooling over Northern Australia: the importance of oceans under a warming climate.

Summer rainfall over northern Australia (NA) is the largest water source of Australia. This study reports a new dominant wetting and cooling pattern over NA in the post-1979 satellite era, contradicting the global mean warming trend. Further investigation reveals that sea surface temperature (SST) in the Tropical Western Pacific (TWP) is the controlling factor responsible for recent NA rainfall increase. We identify that direct thermal forcing by increasing SST in this region leads to anomalously high rainfall. As such, the increasing SST in the TWP induces over 50% of the observed rainfall wetting trend over NA. This increased rainfall in turn induces land surface cooling in NA. This mechanism can be confirmed with results obtained from sensitivity experiments of an atmospheric general circulation model. Thus, increasing SST in the TWP has contributed much of the recent summer rainfall increase, and consequently, the surface cooling over NA. Our results have implications for understanding regional climate change in the Tropics and highlight the importance of ocean processes. (with Jingjing Yu, National Meteorological Information Center, China Meteorological Administration, Beijing 100081, China and Yun Li, CSIRO Mathematics, Informatics and Statistics, CSIRO Climate Adaptation Flagship, Floreat, Western Australia 6014, Australia)


Nathan Mayne, University of Exeter

Title: Developing a unified framework for modelling (exo)planets.

Abstract: The first detection of an exoplanet, or planet outside our solar system, was made over twenty years ago. The number of detected planets has rapidly increased over these two decades, and the field, driven by the huge diversity of planetary states, has transitioned to an era of characterisation. Observations have now provided, in some cases, glimpses of the atmospheric state of these atmospheres providing constraint on compositions, temperatures and even wind speeds.

At the University of Exeter, in collaboration with the UK Met Office, we are developing a theoretical framework with which to interpret current, and future observations of exoplanets and place them in context with our own planet.

I will present an overview of the observational constraints for exoplanets, outline the main puzzles and challenges and summarise attempts to interpret these observations. I will also detail our own work on this subject, and outline how we are embedding our research within the model framework of the UK Met Office. Finally I will look ahead and what to expect from the field of exoplanet research in the coming years.


Sofia Olhede, University College London

Title: Big Oceanic Data in Time

Abstract: Observations relevant to out understanding of the global climate system are highly structured: taking the form either of temporal observations, or spatially structured data. Analysis is normally challenged by sheer volume of data, and so algorithmic choices become important. I will discuss stochastic modelling of global scale observations of ocean circulation, and what we can understand from such observations.

This is joint work with Jeffrey Early, Shane Elipot, Arthur Guillaumin, Jonathan Lilly & Adam Sykulski.


Andrew Stuart, University of Warwick.

Title: Blending Mathematical Models and Data: Algorithms, Analysis and Applications

Abstract: Many problems in the sciences and engineering lead to the inverse problem of determining an unknown set of parameters, or field, which is input
data for a mathematical model, from a finite set of indirect measurements of the system being modelled. Accurate estimation of these parameters is of crucial importance for the predictive capability of the models. Climate modelling provides a prime example of a field where this inverse problem is a key step.  Other examples include oceanography, weather forecasting, personalized medicine and the modelling of human behaviour. In this talk we discuss the inverse problem of blending models with data, highlighting generic issues which arise, and showing the role of the mathematical sciences in developing a methodological approach to this problem. The aforementioned applications will be used to illustrate the ideas.


Geoff Vallis, University of Exeter

Title: From theory to numerical simulation in understanding climate on Earth and other planets.

Abstract: I will discuss two related topics in climate dynamics. First, what are some of the scientific problems? Second, how should we address these problems, and in particular what is the relation of ‘theory’ to numerical simulation?

After a brief overview of the main scientific problems, I will discuss the methodology. Often we use large and complicated numerical models to address the problems. Is this the best way? Does ‘theory’ in the conventional sense — elegant equations making testable predictions — still have a role? Perhaps numerical models are our modern-day theory? Throughout the talk I’ll pose questions as much as answer them and I’ll be giving my opinion on the matters, not necessarily the consensus of the community.