The role of natural aerosol in biosphere-atmosphere interactions and feedbacks

This project will investigate the role of natural aerosol in vegetation-climate feedbacks, using state-of-the-art models to improve our understanding of biosphere-atmosphere interactions with important implications for future climate projections.

Background

Natural aerosols play an important role in vegetation-atmosphere-climate interactions. The terrestrial biosphere and the oceans are a large source of atmospheric aerosols, such as secondary organic aerosol (SOA), biomass burning from wildfires, dimethyl sulfide (DMS) from plankton, and sea-salt. Once in the atmosphere, these natural aerosols affect climate through their direct and indirect radiative effects. In addition, through their induced changes on diffuse surface radiation, these aerosol can strongly affect land vegetation growth. Plant photosynthesis is more efficient under diffuse radiation conditions, an effect known as diffuse radiation fertilisation which is essentially due to deeper canopy light penetration. Previous work from our group quantified the diffuse radiation fertilisation effect from biomass burning and biogenic secondary organic aerosol, highlighting its large impact on the terrestrial carbon cycle.

In turn, the abundance and distribution of natural aerosol is controlled by changes in climate. For example, biogenic aerosol emissions from land vegetation are strongly constrained by temperature, precipitation and radiation.
While substantial progress has been made in recent years in this area, there are still many uncertainties in the current understanding of these complex interactions and feedbacks. In particular, the role of competing effects such as diffuse radiation fertilisation and temperature reduction, together with additional changes in soil moisture remains largely unexplored.
We now 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.

Objectives

The overarching aim of this project is to analyse and quantify the role of natural aerosol in the various vegetation-atmosphere-climate feedback mechanisms. The approach will likely involve a combination of global aerosol, radiation and vegetation models, together with simulations using the new UK Earth System Model (UKESM).

While relatively flexible to allow for your interests, the studentship is likely to involve:

• A comprehensive assessment of regional and global natural aerosol emissions (with the associated uncertainties), both from process-based and from empirical models.
• Examining the role of natural aerosol in the observed NPP regional trends in recent decades.
• Exploring the extent to which anthropogenic aerosol and other pollutants (e.g. ozone) have affected the efficiency of these ecosystem feedbacks.
• Investigating the effect of temperature and atmospheric carbon dioxide changes on these interactions during the last few decades.
• Using future simulations to estimate how climate change is likely to affect these feedbacks.
• Assessing the role of these feedbacks in the terrestrial carbon cycle, testing the hypothesis that they are responsible for the budget imbalance in the global carbon budget.

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.