GSI Seminar Series – Dr Femke Nijsse and Dr Kirsten Lees: ECR Special

Taken from GSI Seminar coordinator Daneen Cowling’s Blog 

For the final seminar of the term we hosted an Early Career Researcher special event. We were excited to host a pair of impressive researchers within the GSI; Dr Femke Nijsse and Dr Kirsten Lees.

Dr Femke Nijsse: Emergent constraints on climate sensitivity from historical warming and models

Dr Nijsse gave a talk on her the work of her PhD exploring the climate model uncertainties on both transient timescales and long-term projections. Dr Nijsse introduced the difficulty around predicting climate change: bottom-up methods which use climate models and are limited by feedback and aerosol uncertainty. While top-down methods which use accurate historical temperature rise and radiative forcing and ocean heat uptake. Emergent contraints modelling permits the use of both of these methods which can provide climate sensitivity.

Dr Nijsse explored ways to address uncertainty – specifically with aerosols, whereby for periods of lesser aerosol influence can be used. How well models are able to constrain estimates, can be explained by grouping their sensitivity. To then apply an Emergent Constraints Model, Dr Nijsse laid out the following methods:

  1. Use historical warming since 1975 (for relative aerosol stability)
  2. Compute model ECS and TCR
  3. Model historical warming
  4. Determine function form of emergent constraint

Dr Nijsse also exposed how the ratio relationship between ECS and TCR can increase with climate sensitivity, as some models with a moderate TCR values can exhibit a higher range of ECS values. From her research, Dr Nijsse concluded it would be unlikely for an ECS > 4.5 K and TCR > 2.5 K. ECS may also be restricted using ocean heat uptake.

To end her seminar, Dr Nijsse also introduced her current work on her postdoc with the Economics of Energy Innovation and System Transition Project. The project is an international effort to enhance energy-environment-economy models, and integrate non-equilibrium ideas into equilibrium models. Dr Nijsse is modelling the challenges of renewable energy – from variability in wind and sun production to diffusion and learning of cost and storage.

Dr Kirsten Lees: Peatland Resilience

Dr Lees talk was on her Peatland Resilience research. Introduced with what Peatlands are and the suite of ecosystem services they offer – ranging from Carbon storage, flood management and biodiversity. Dr Lees then explained how to assess the resilience of these systems, using indicators from remotely sensed data. To measure resilience, the following steps can be applied to a site:

  1. Choose a resilience metric
  2. Detect a disturbance event
  3. Measure recovery time

Dr Lees has applied these steps to water levels and vegetation burn recovery to understand peatland resilience. From her analysis, Dr Lees suggests a complex interaction of factors influencing peatland resilience. Restoration and wildfire are factors with the most potential to alter peatland resilience, and so will be important to observe in the future.

This seminar was a great opportunity to hear about the impressive work being done by researchers at the start of their career, as well as a fresh insight into the diverse research of the GSI.

To watch these two talks and the questions from the audience, click this link.

If you would like to give a talk at a future seminar, please contact event organisers Daneen Cowling ( and Guy Lomax (

Stay on These Roads

A Note from Tim (Global Systems Institute Director)

I have been hunting high and low for examples of positive tipping points towards sustainability. Collaborating with Simon Sharpe in the UK Cabinet Office COP26 team we recently showed  a clear tipping point in the uptake of electric vehicles in Norway – where they cost the same to buy as a petrol or diesel car thanks to policy incentives. But it turns out there is more to this story than enlightened top-down governance. My train of thought was happily disrupted on discovering Robbie Andrew’s twitter thread  showing how pop band A-ha played a decisive role in introducing electric car incentives in Norway. It beautifully illustrates how apparently small actions can lead to transformative social and technological change. We all need to stay on these roads, or rather join A-ha and Norway on them.

Posted 18/03/2021

GSI Seminar Series – Dr Kimberley Simpson: Whodunnit? The Case of the Vanishing Savannas

Taken from GSI Seminar coordinator Daneen Cowling’s Blog 

The delicate balance between C3 trees and C4 grasses that has characterised the global Savannahs for millennia is now being compromised, threatening the existence of this biome. In this seminar, Dr Simpson assesses the potential ‘culprits’ behind the case of the vanishing Savannas,

Dr Simpson is a postdoctoral researcher at the University of Sheffield, in the department of Animal and Plant Science within the Osbourne Lab. Dr Simpson is broadly occupied in how processes create and maintain phenotypic diversity and how traits influence such processes. She is currently involved in a project investigating abiotic and biotic factors in woody encroachment in Savannas. She collaborates on field work with Rhodes University in South Africa, and is expanding on her PhD which investigated fire influence on grass functional traits.

To layout her investigation of what is causing a reduced Savanna, Dr Simpson first explained the context of the ‘victim’ in the case – the characteristics and geographic distribution of Savannah ecosystems. Then the ‘crime’ – the encroachment of trees and diminishing Savannah grasslands. Although the increased tree cover could have benefits in the form of increased fuel wood and Carbon sequestration, negative implications in the form of reduced foraging, groundwater, visibility and ecotourism also occur. But most detrimental, the shift threatens the many species reliant on these open landscapes.

Dr Simpson took the audience through a storyboard of potential ‘suspects’:

  1. Reduced Fire Frequency: Intensive grazing and fragmentation is contributing to a reducing in fire frequency. This is detrimental for grasses that are able to thrive and out-compete trees in systems of high fire frequency due to faster regeneration and shorter life-cycles of grasses relative to trees. Changes in fire frequency also drive phenotypic divergence in Savanna grasses, with a reduction coinciding with a reduction in ‘seeder’ species. This creates a feedback whereby fire frequency changes alter community composition, which as a result changes flammability. Current observations show a reduced fire frequency = more trees can reach maturity = grass biomass reduces = reduced flammability contributing to the reduced fire frequency trend.
  2. Elevated CO2: C3 trees have a high growth response to elevated CO”, whereas C4 grasses do not. But – elevated CO2 cannot explain the spatial variability in savanna change.
  3. Rainfall: Encorachment also correlates with rainfall and likely interacts with CO2 via stromata – C4 grasses have an improved photosynthetic rate during drought, whereas C3 trees respond well to high CO2 and H2O.

Dr Simpson concluded her investigation with the verdict: more evidence is needed!

In her upcoming projects, Dr Simpson hopes to unpick the various interactions, as well as the role of plant functional traits, as the case of the Savanna encroachment continues. Dr Simpson also hopes to investigate new influences in the case – such as the role of elephants able to bulldoze trees to maintian the ecosystem, and the controls of species that allows some to proper better than others.

To watch the recording of Dr Simpsons talk and the Q&A, click this link.