Sample thesis project descriptions

Theme 1: Downscaling and probabilistic forecasting

Projecting the future change in avalanche frequency using climate downscaling

The Trans-Canada Highway (TCH) is the primary connection between British Columbia (BC) and the rest of Canada. One of the most challenging sections of the TCH is between Sicamous, BC and the Alberta border. The difficult terrain, including climbing over Rogers' Pass at a maximum elevation of 1330 m and over 200 avalanche paths along this section of the highway, make it subject to many natural hazards including slope stability issues and snow avalanches. Historically, seasonal closures can amount to an average of over 60 hours on some sections of the TCH. Given the difficult geography of the corridor seasonal closures are necessary and some amount of closures will always occur; however any reduction in duration or frequency will positively benefit the reliability of the corridor and the economy.

The goal of this project is to use existing climate (including avalanche) information to develop indices that link avalanche occurrence to the distribution of particular weather events. Through the use of either dynamical or statistical downscaling, future changes in these indices will be examined.

This project will be conducted in partnership with the BC Ministry of Transportation and Highways and the Pacific Climate Impacts Consortium.

Theme 2: Coastal ocean and terrestrial ecosystems

The significance of intermittency in ocean circulation especially with regard to chemistry and biology of the coastal ocean

The pH and oxygen concentration in coastal waters are determined by a complex interplay of physical circulation, ocean chemistry, and biological processes. Coastal wind patterns play a major role in determining circulation and vary on daily timescales. On the Pacific coast of North America these winds drive intermittent pulses of upwelling and downwelling, depending on location and season. Upwelled waters are low in oxygen and high in carbon but drive ocean production which replenishes oxygen and draws down carbon in the short term (days). In the longer term the degradation of organic matter depletes oxygen and releases carbon (months). The net result is an unusually large range in concentrations of both oxygen and carbon in these upwelling regions. Marine organisms are particularly sensitive to the timing and extremes in these concentrations.

This project will investigate the significance of intermittency in ocean circulation on the chemistry and biology of the coastal ocean, with a primary focus on ocean acidification and hypoxia. The starting point for the investigation will be an idealised model of coastal coupled physical-biogeochemical cycles. This model can be used in its existing configuration to study proceses controlling ocean pH, and extended to consider hypoxia through incorporation of an oxygen cycle.

This project will be conducted in partnership with the Institute of Ocean Sciences.

The role of dimethylsulfide in the climate system and feedbacks to future climate changes

Dimethylsulfide (DMS) produced by plankton in the surface ocean is the largest natural source of reduced sulfur to the atmosphere and a potentially important regulator of climate through formation of cloud condensation nuclei. Enhanced DMS fluxes to the atmosphere are likely to generate a cloudier and cooler climate, but it remains an open question whether anthropogenically induced changes to ocean circulation, chemistry, and biology will enhance or suppress DMS efflux. We are seeking a PhD student to work with experts in atmosphere and ocean modelling to assess the different ways in which DMS sources to the atmosphere can be represented in climate models and assess the implications of changing DMS sources for atmospheric aerosol processes and future climates.

Theme 3: Projection, detection, and attribution of climate change

Observational constraints on future climate change

Climate models represent the best available tools for projecting future climate change, providing key information necessary to inform decisions on climate change adaptation and mitigation to policymakers and society at large. However, due to the many complexities of the climate system and uncertainties in its properties, climate model projections of future change in many aspects of the climate differ strongly between models. It has often been standard practice to report projected future climate change as an average of climate model projections, with an uncertainty range based on the inter-model spread. However, if a relationship across models exists between a projected future change in some variable, and something which can be directly observed, then we can use this relationship to constrain our projections. For many aspects of projected future climate change it is challenging to find a linearly related observable quantity: However several studies have begun to identify variables in which such relationships are apparent. For example models which simulate more warming over the historical period tend to simulate more warming in the future; the strength of the snow albedo feedback on the seasonal cycle and on climate change are proportional; and the sensitivity of shifts in the Southern Hemisphere jet to greenhouse gas increases is related to the mean position of the jet. This project will either use one or more such known relationships or search for other new relationships between a projected climate change and observable quantity, and then apply these relationships to improve our projections of 21st century climate change.

Constraining the precipitation response to geoengineering by sulphate aerosol injection into the stratosphere

The injection of stratospheric aerosol into the stratosphere has been proposed as perhaps the most technically feasible geoengineering approach to slowing or reversing global warming (Blackstock et al., 2009). Some model simulations suggest that such aerosol injection into the stratosphere would not only reduce warming, but would also largely cancel the greenhouse gas influence on precipitation, with the combination of stratospheric aerosol and greenhouse gas increases resulting in a relatively benign net influence on global precipitation (Blackstock et al., 2009). However, climate models tend to underestimate the rainfall response to volcanic aerosol by a large factor, a close analogue of proposed sulphate aerosol injection. Further, it is likely that in some regions, such as the subtropics, greenhouse gas and stratospheric aerosol effects would add to cause a large net decrease in precipitation.

The project would therefore start by investigating the precipitation response to volcanic eruptions and greenhouse gas increases in a range of existing coupled climate model simulations and comparing these with observations. Models could be compared in order to identify those model features and physical processes associated with the simulation of a more realistic precipitation response to stratospheric aerosol. The successful applicant would go on to carry out simulations of the climate response to stratospheric aerosol injection using the Canadian Centre for Climate Modelling and Analysis coupled model, along with similar simulations of the climate response to volcanic eruptions which could be compared with observations. If possible the model or specified forcings might be modified in order to allow more realistic simulation of the precipitation response to historical volcanic eruptions, or otherwise the projected precipitation response to stratospheric aerosol injection might be appropriately scaled based on the simulated volcanic response. In this way better estimates of the precipitation response to stratospheric aerosol injection could be derived, and their impacts assessed.

The impact of the vertical decay scale for turbulence on the large-scale ocean circulation and climate

Observations indicate that intense mixing in the ocean is localized above complex topography. In particular, evidence for elevated values of vertical diffusivity has been found above the mid-ocean ridges (e.g., Mauritzen et al., 2002) and in the Southern Ocean (e.g., Naveira Garabato et al, 2004). Some modeling studies indicate that accounting for this fact can be important. In particular, it was illustrated that, e.g., the oceanic heat transport and the structure of large-scale potential vorticity in the abyssal ocean can be strongly affected (e.g., Simmons et al., 2004; Saenko and Merryfield, 2005). Recent observations indicate that there is a large uncertainty not only in the horizontal structure of the small-scale mixing, but also in its vertical structure (e.g., Kunze et al., 2006; Decloedt and Luther, 2010). Scaling arguments suggest that this could imply a rather large uncertainty in the amount of deep water that can upwell through the stratified, low-latitude ocean (Decloedt and Luther, 2010). Furthermore, idealized-basin model experiments point at the potential impact on the oceanic heat uptake (Saenko, 2006) and even multiple climate states (Schmittner and Weaver, 2001).

The aim of this project is to further investigate the impact of the vertical decay scale for small-scale turbulence on the large-scale oceanic circulation and climate. To this end, we plan to run both ocean- only and fully coupled experiments varying the decay scale in the Simmons et al. (2004) tidal mixing scheme. The ocean-only experiments will be run for 10 000 years using the CCCma ocean model (which is a version of the Geophysical Fluid Dynamics Laboratory Modular Ocean Model). As the first step, we feel that it is important to make sure that the model is capable of reproducing the observed structure of large-scale potential vorticity (PV) and that bottom pressure torques play an important role in closing the PV balance. Next, the focus will be on the impact of the vertical decay scale for turbulence on the structure and budget of PV, including in the deep ocean. (Simple, PV-based arguments can be used to relate large-scale meridional flows in the ocean to vertical diffusivity, so it is expected that by changing the vertical decay scale for mixing, the PV budget and the meridional flows should also be affected).

The second stage of the project will involve running the CCCma fully coupled model, both under 1ŚCO2 and 2ŚCO2 scenarios. Here we aim to address, among other questions, the importance of the vertical decay scale for turbulence on the response of (a) surface climate, (b) oceanic heat uptake (c) ocean gyre and overturning circulations.