Overview

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.

Dust export from the Sahara captured in 3D by NASA’s CALIPSO mission.

Methodology

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.

 

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes.  This project will provide the student with significant training in high performance computing, using complex numerical models of the Earth System, and meteorology and climate change science.

Timeline

Year 1: Climate simulations for present day: what is the impact of desert area and its dust export today?

Year 2: Simulations testing the impacts of the formation of the desert, and/or the mid-Holocene, when records show an extensive ‘Greening’

Year 3: Future simulations – what is the role of elevated CO2 versus land use?

Further Details

Dr Peter Hopcroft, School of Geography, Earth & Environmental Sciences, University of Birmingham: email: p.hopcroft@bham.ac.uk.