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Greenland/Antarctic ice sheet mass balance and regional variability in sea level rise

Professor Andy Shepherd (SEE), Dr Anna Hogg  (SEE)

Project partner(s): Centre for Polar Observation and Modelling (CPOM); European Space Agency (ESA)

Contact email: a.e.hogg(at)leeds.ac.uk

Application deadline: 1st March 2017

PhD start date: 1 May 2017 (negotiable)

Funding for this project is linked with the European Space Agency’s Climate Change Initiative.  The 3 years funding award will pay UK/EU tuition fees and UK research level stipend (£14,510 for 2017/18).  The Greenland Ice Sheet fieldwork component is supported by alumni donation. 

Project Summary

This project offers an exciting opportunity to work at the interface of climate and space science, making an important contribution to international efforts to study the effects and impacts of climate change.  Importantly, it includes a field campaign on the Greenland Ice Sheet to undertake vital work to ensure that future estimates of ice loss are correct. 

Based within the Centre for Polar Observation and Modelling (CPOM), the project will be co-funded by the European Space Agency (ESA).  As a result there will be opportunities to attend international ESA meetings and engage with a wide range of scientific collaborators.

During this project you will use Earth Observation data acquired by satellites such as CryoSat-2, ESA’s mission dedicated to monitoring the polar regions, to assess how the Greenland and Antarctic ice sheets are contributing to sea level rise (SLR), and how this sea level contribution varies spatially and temporally across the globe. The resulting ice sheet “fingerprints” will not only add confidence to current assessments of climate change impacts but also improve future regional SLR projections.

In addition, you will collect field data and use it to validate satellite measurements from CryoSat-2, needed to assess how CryoSat-2’s measurements are distorted by climatic extremes, and therefore to improve current estimates of ice loss and SLR.

Background

Fluctuations in the mass of the Greenland and Antarctic ice sheets impact directly on global sea levels: since 1901, ice losses from Antarctica and Greenland, alongside small glaciers and ice caps and thermal expansion of the oceans, have caused global sea levels to rise at a rate of 1.7 mm/yr.  Between 1992 and 2010 the rate of change, as measured by satellite altimetry and tide gauges, reached 3.2mm/yr (IPCC AR5). 

These observations also show that SLR is not occurring uniformly across the globe.  With sea levels likely to rise at an even faster rate during the 21st century, affecting more than 70% of coastlines by 2100 and representing a major threat to low-lying, highly populated coastal regions of the world in particular, it is increasingly important to be able to measure and understand each separate contributor to SLR.

Identifying the specific contribution from the polar ice sheets is possible through a technique known as “fingerprinting”.  Several approaches have evolved from the original sea level equation of Farrell and Clark (1976), consistently showing patterns characterised by a large amplitude fall in sea level adjacent to the ice sheet (due to loss in gravitational attraction associated with the diminished ice mass) and a gradual rise moving away from it (e.g. Hay et al., 2015, Fig. 1).

Figure 1:  Normalised sea-level changes due to rapid melting of the Greenland (a) and West Antarctic Ice Sheet (b) (Hay et al., 2015)

Recent ice sheet fingerprinting studies have focused on gravimetry data (from NASA’s GRACE mission), covering the period 2003-2009 (e.g. Bamber and Riva, 2010, Riva et al., 2010).  

As part of ESA’s Antarctic and Greenland Climate Change Initiative (CCI), CPOM has demonstrated how the ice sheets are changing using satellite altimetry (ERS-1/2, ENVISAT and CryoSat-2), making full use of the historical and new satellite Earth Observation datasets. This 25 year long, continuous satellite data record currently provides the most reliable estimate of the spatial pattern and onset of ice sheet mass loss.  Dating back to the early 1990s, it also provides the longest continuous record of ice sheet change.

However, external events can complicate satellite measurements of ice sheet thickness change. In 2012 there was an extreme summer melt event on the Greenland Ice Sheet where more than 99 % of the ice sheet surface melted. Snow melt triggered an abrupt change in the way satellites, such as CryoSat-2, sample the ice sheet in the dry snow zone due to a change in the radar altimeter scattering horizon. Validation experiments are needed to characterise and correct for such events to improve the accuracy of satellite measurements of ice loss from Greenland.

The next steps are therefore to a) use existing quantitative information on ice mass loss from the Greenland and Antarctic Ice Sheets to create an assessment of the global, and spatially variable regional, ice sheet SLR contribution; and b) improve radar altimetry estimates of ice sheet mass loss, with a particular focus on characterising how the existing satellite measurement techniques are effected by extreme melt events, which are projected to increase in frequency in the future.

Objectives

The aim of this project is to generate a sea level rise fingerprint for both the Antarctic and Greenland Ice Sheets (separately and combined), using data from historical and present day satellite altimetry missions.

Specifically, you will: 

  1. Produce a comprehensive and detailed picture of how changes to the Greenland and Antarctic Ice Sheets are impacting on sea levels, focusing on regional variations in SLR.
  2. As part of a broader research team, investigate the impact of the 2012 Greenland melt event by collecting and analysing field measurements from the Greenland Ice Sheet, integrating them with satellite observations, and promoting the findings.
  3. Make a significant contribution to the ESA CCI, including reducing current uncertainties in SLR and its individual components, and assessing the potential of this information to improve predictive climate/SLR models. 

The fieldwork component of the project is funded through alumni donation.  You will also therefore be required to produce a number of short written reports to the funder at regular intervals throughout your studentship.

Training and support

The student will work under the supervision of CPOM Director Professor Andy Shepherd and ESA Living Planet Research Fellow Dr Anna Hogg.

A studentship within CPOM provides a fantastic opportunity to actively collaborate with a large team of land and sea ice observation and modelling experts at universities across the UK. The project provides a high level of training in: (i) satellite remote sensing; (ii) polar fieldwork; (iii) glaciology; (iii) data analysis and visualization; (iv) calibration and validation of satellite systems; and (v) scientific writing – we strongly support students to write publications during their PhD.

The successful applicant will also have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of training workshops in numerical modelling, through to managing your degree, to preparing for your viva. A full list of training opportunities is available.

Requirements

A good first degree (first or high 2.i) or Masters degree in physics, maths, Earth science, climate science, Earth observation or a related discipline. Expertise in computer programming, while not required, will be a valuable asset.

References

Bamber, J. & Riva, R. (2010) The sea level fingerprint of recent ice mass fluxes, The Cryosphere doi:10.5194/tc-4-621-2010

Farrell, W. E. & Clark, J. A. (1976) On postglacial sea level, Geophysical Journal of the Royal Astronomical Society doi:10.1111/j.1365-246X.1976.tb01252.x

Hay et al. (2015) Probabilistic reanalysis of twentieth-century sea-level rise, Nature doi: 10.1038/nature14093

Riva et al. (2010) Sea-level fingerprinting of continental water and ice mass change from GRACE, Geophysical Research Letters doi:10.1029/2010GL044770