PhD Studentship: Role of the Sahara and Saharan dust in global climate

The Sahara desert is the largest such area on Earth today. Its climate is, in places hyper-arid, with little annual rainfall, little to no vegetation and scarce human inhabitation. The Sahara also export millions of tons of desert dust to the atmosphere, making it one of the main natural sources of atmospheric aerosols. Saharan dust, which is occasionally deposited as far afield as the UK, is thought to modulate the climate of the north Atlantic by reflecting and absorbing light in the atmosphere, and by changing the distribution of clouds. Furthermore, the dust contains much needed nutrients for plant and ocean biology, and so is thought to have a fertilizing effect in both the tropical Atlantic and the Amazon rainforest.

The Sahara is also unique in terms of its history. It is thought to have formed around 7 million years ago, but since then, has repeatedly ‘Greened’ in response to natural climate variations. The causes of the wetter conditions that contributed to the most recent ‘Greening’ (9000-4000 years ago) remain only partially understood. The state of the Sahara is also thought to have played pivotal role in the migration of modern humans out of Africa. In the future, increased atmospheric CO2 will potentially fertilize vegetation in the region, greening the southern boundary of the Sahara (the Sahel) and thereby reducing the desert area.

Overall several uncertainties persist that this project will address. The Sahel is a known hotspot for atmosphere-land-surface coupling in terms of climate change, which makes it an important region to understand in a global context. Further, the interactions between the North African monsoon regime and dust-climate effects are not fully understood. One missing component to date, is the indirect effect of dust on clouds.

In this project you will use the UK Earth System model, configured for current, past and future conditions, to quantify the role of the Sahara and its dust export on the climate system to provide a comprehensive understanding of the changing role of the desert in the climate system.

The UK Earth System Model (UKESM) is a joint development by the UK Met Office and a consortium UK universities. It is a state-of-the-art numerical representation of the climate system, derived from the Met Office weather prediction suite. UKESM is internationally leading in its representation of tropical climate variability, clouds and aerosols, including dust. It provides a unique opportunity to better understand couplings in the Earth System, particularly as related to aerosols and vegetation.

In addition to current and future setups, the model will be configured for past time periods. These will include the last ‘Green’ episode, and the late Miocene, when the desert formed. An ensemble of simulations will quantify the climatic influences from the desert itself, and the separate influences from desert dust on the atmosphere-ocean system, on clouds and on biogeochemical cycling.

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will received the following financial support.

Annual stipend, set as £14,553 for 2017/18

Research training support grant (RTSG) of £8,000

CENTA students are required to undertake 45 days training throughout their PhD including a 10 day placement.

References

Sagoo, N., and T. Storelvmo (2017), Testing the sensitivity of past climates to the indirect effects of dust, Geophyical Research Letters, 44, doi:10.1002/2017GL072584.

Pausata, F. et al. (2016), Impacts of dust reduction on the northward expansion of the African monsoon during the Green Sahara period, Earth & Planetary Science Letters, 434: 298–307, doi: 10.1016/j.epsl.2015.11.049.

Bathiany, S. et al. (2014), CO2-Induced Sahel Greening in Three CMIP5 Earth System Models, Journal of Climate, 27, 7163-7184 doi: 10.1175/JCLI-D-13-00528.1.

Schuster, M. et al. (2006), The Age of the Sahara Desert, Science, 311 (5762), 821: doi: 10.1126/science.1120161.

Zhang, Z. et al. (2014), Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene, Nature, 513, 401-404: doi: 10.1038/nature13705.