The role of aerosol radiative effects in the global carbon budget

This exciting project will address the global carbon cycle budget imbalance term by using state-of-the-art global models and observations to comprehensively analyse the role of aerosol radiative effects on the land carbon sink.

Fig. 1: Diffuse light fertilisation from Biogenic Volatile Organic Compounds. Globally, forests get twice as much benefit through increased photosynthesis due to diffuse light fertilisation. From Rap et al. (2018).

Background

Since the Industrial Revolution atmospheric CO2 concentrations have increased by 50%, from 278ppm in 1750 to over 415ppm today, contributing about 80% of the total anthropogenic radiative forcing on climate. This dramatic increase has so far been mitigated by the land and ocean carbon sinks absorbing over half of the total CO2 emitted by human activities (Friedlingstein et al., 2020). Accurate estimates of these carbon sinks is essential for projecting future climate change and developing effective climate policies. Historically calculated as a residual of all other carbon budget terms, the land carbon sink has only recently started to be quantified directly using global vegetation models. However, as these models do not currently include important processes such as diffuse light fertilisation (see Fig. 1; Mercado et al., 2009; Rap et al., 2018), it meant that a new “budget imbalance” term had to be introduced to fully close the carbon budget equation.

Objectives

The overarching aim of the project is to reduce the global carbon cycle budget imbalance term via improved understanding of the land carbon sink. 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 remote sensing analysis (e.g. Global Ecosystem Dynamics Investigation – GEDI; Clouds and the Earth’s Radiant Energy System – CERES) and model simulations (i.e. aerosol, radiation and vegetation models, together with UK Earth System Model simulations).

Within the diverse supervision team we have the ability to observe and simulate biosphere-atmosphere 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 satellite observations and global models to answer a series of key questions. While relatively flexible to allow for your interests, the project will involve:

  • A comprehensive assessment of global forest structure and above-ground biomass density using remote sensing products.
  • Using global models evaluated against satellite and surface observations to understand the role of aerosols in recent Net Primary Productivity trends.
  • 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 biosphere-atmosphere interactions.
  • Using future simulations to estimate how climate change is likely to affect ecosystem feedbacks.

Potential for high impact outcome

There are still large uncertainties in our understanding of how the terrestrial carbon cycle has changed in recent decades and how it is likely to evolve in the future. With access to cutting-edge techniques and support from our world leading research groups, this project will improve our understanding of biosphere-atmosphere interactions and feedbacks that may have important implications for future climate projections. This will likely be of interest to both the general public and to policy makers working in climate mitigation and forest conservation. It is expected that findings of this project will be published in high impact journals and will be presented at international conferences.

Training

The student will work under the supervision of Dr Alex Rap and Prof Dominick Spracklen and will be a member of the the Biosphere Processes and Climate Group in SEE. They will also be supervised by the external co-supervisors Dr Lina Mercado (Exeter), Dr Steven Hancock (Edinburgh) and Dr Ben Johnson (Met Office). The project provides an exciting opportunity to exploit the new UK Earth System Model (UKESM). The student will also be part of the Priestley International Centre for Climate that brings together world leading expertise in all the key strands of climate change research at the University of Leeds. 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.

References

  1. Friedlingstein, P., et al. (2020), Global Carbon Budget 2020, Earth Syst. Sci. Data, 12, 3269-3340.
  2. Mercado, L., et al. (2009), Impact of changes in diffuse radiation on the global land carbon sink, Nature, 458(7241), 1014.
  3. Rap, A., et al. (incl. Mercado, L., Spracklen, D.V.) (2018), Enhanced global primary production by biogenic aerosol via diffuse radiation fertilisation, Nature Geoscience, 11(9), 640-644.