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The global carbon cycle budget imbalance

Project Description

This project will use state-of-the-art models to investigate the extent to which improved representation of biosphere-atmosphere processes reduces the global carbon cycle budget imbalance.

Since the Industrial Revolution atmospheric CO2 concentrations have increased by almost 50%, from 278ppm in 1750 to over 410ppm today. This dramatic increase has already had important consequences on the Earth’s climate, exerting a forcing which represents approximately 80% of the total anthropogenic radiative forcing on climate (Myhre et al., 2013). Substantial progress has been made in recent years in our understanding of the global carbon budget. We now know that only about 40% of the total CO2 emitted by human activities remains in the atmosphere, while more than half is absorbed by the land and the ocean. However, many uncertainties still remain, especially in terms of the land carbon sink which historically has been estimated as a residual of all other terms. It is only in the last couple of years that this land sink term began to be estimated directly, using global vegetation models. This led to the introduction of a new “budget imbalance” term which is now needed to fully close the carbon budget equation (Le Quere et al., 2018).
The most probable cause for this budget imbalance are believed to be errors in the land and ocean sink terms (Le Quere et al., 2018). These errors are likely caused by current models not including important processes such as, for example, diffuse radiation fertilisation which has been shown to have substantial effects on land vegetation growth (Mercado et al., 2009; Rap et al. 2015; Rap et al., 2018).

The aim of this project is to quantify to what extent improved modelling of the land carbon sink can reduce the global carbon cycle budget imbalance term. In particular, the project will investigate the role of competing effects on the land carbon sink due to variability in temperature, precipitation and diffuse radiation. The approach will involve a combination of global aerosol, radiation and vegetation models, together with simulations using the new UK Earth System Model.

We have at Leeds the ability to represent these interactions in a more comprehensive way than ever before. This project will therefore provide an exciting and unique opportunity to employ state-of-the-art global models to answer a series of key questions. While relatively flexible to allow for your interests, the project is likely to involve:
• A comprehensive assessment of variability in natural and anthropogenic aerosol emissions (with the associated uncertainties), both from process-based and from empirical models.
• Examining the role of aerosol in the observed NPP trends in recent decades.
• Exploring the extent to which anthropogenic aerosol and other pollutants (e.g. ozone) have affected the efficiency of ecosystem feedbacks.
• Investigating the effect of changes in temperature, precipitation and atmospheric CO2 on these interactions during the last few decades.
• Assessing the role of these feedbacks in the terrestrial carbon cycle, i.e. addressing the global carbon cycle budget imbalance.
• Using future simulations to estimate how climate change is likely to affect these feedbacks.

The student will work under the supervision of Dr. Alex Rap and Prof. Dominick Spracklen and will be a member of two very active and supportive research groups in SEE, the Biosphere Processes Group and the Physical Climate Change Group. The project provides an exciting opportunity to exploit and to provide training in the new UK Earth System Model (UKESM). The student will also be part of the Leeds Ecosystem, Atmosphere and Forest (LEAF) research centre at the University of Leeds that brings together researchers from across the Campus. Through the high level specialist scientific training associated with this project, the student will develop a comprehensive understanding of vegetation-atmosphere interactions and will work with state-of-the art global land-surface and atmospheric composition-climate models. In addition, the student will learn how to communicate science and how to write high impact journal publications.

The student will collaborate closely with Dr Richard Ellis from the Centre for Ecology & Hydrology (CEH) Wallingford who will provide guidance and expertise on the land-surface component of the UKESM model.

More details:

Funding Notes

This project is available for funding through the Panorama NERC DTP, please see View Website for funding details and eligibility requirements.


1. Le Quere, C., et al. (2018), Global carbon budget 2017, Earth Syst. Sci. Data, 10, 405–448.
2. Le Quere, C., et al. (2018), Global carbon budget 2018, Earth Syst. Sci. Data, 10, 2141-2194.
3. Mercado, L. M., et al. (2009), Impact of changes in diffuse radiation on the global land carbon sink, Nature, 458(7241), 1014–1017.
4. Myhre, G., et al. (2013), Anthropogenic and natural radiative forcing, in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, edited by T. F. Stocker et al., pp. 659–740.
5. Rap, A., Spracklen, D.V., Mercado, L., Reddington, C.L., Haywood, J.M., Ellis, R.J., Phillips, O.L., Artaxo, P., Bonal, D., Restrepo Coupe, N., Butt, N. (2015), Fires increase Amazon forest productivity through increases in diffuse radiation, Geophys. Res. Lett., 42, 4654-4662.
6. Rap, A., Scott, C.E., Reddington, C.L., Mercado, L., Ellis, Garraway, S., Evans, M.J., Beerling, D., MacKenzie, A.R., Hewitt, C.N., Spracklen, D.V. (2018), Enhanced global primary production by biogenic aerosol via diffuse radiation fertilisation, Nature Geoscience, 11(9), 640-644.

How good is research at University of Leeds in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 79.20

Research output data provided by the Research Excellence Framework (REF)

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