Assistant Professor at the Institute for Marine and Atmospheric research, Utrecht (IMAU)

Claudia Wieners works in Earth System Modelling (climate physics), with a sideline in economics and complexity. Her main research interest is to assess if - and how - Solar Geoengineering could help to mitigate climate change. 

Solar Geoengineering

The aim of Solar Geoengineering, or Solar Radiation Management, is to cool the earth by slightly reducing the amount of incoming solar radiation. The most promising technique consists of imitiating volcanic eruptions by injecting SO2 into the stratosphere (atmosphere aboe ≈15km) to generate a thin veil of cloud that reflects a small fraction of incoming sun light. Of course, this is not really a solution to our climate problem: It is rather like giving a flu patient a paracetamol to bring down the fever; just fighting the symptoms. But what if the "symptom" to be suppressed is an extra meter of sea level rise? Whether Geoengineering could be a valuable complement to (not replacement of!) emission reduction, depends on how efficient it is to reduce adverse effects of climate change, how bad its side effects are, and how expensive it is, and whether humanity manages to govern it wisely. 

Claudia hopes to contribute towards wise decision making about Geoengineering by helping to chart its effects on climate - both beneficial and risky - and investigating simple future scenarios on the possible role of Geoengineering in climate economics. 

Ongoing Projects Geoengineering 

Can delayed Solar Geoengineering revert dangerous climate change? (with PhD candidate Daniel Pflüger)

Current Geoengineering simulations typically assume that Geongineering is started around 2020 - which is obviously not the case. Here we study a dystopic scenario (which we hope will not happen): After decaes of strong CO2 emissions, humanity decides in 2080 that it is "too hot" and attempts to return global mean temperature to 1.5 degrees above pre-industrial. How does this case compare to a world in which Geoengineering has started early? Can effects of the warming - such as weakening of the Gulfstream system (AMOC) be reverted? Simulations are run with the Community Earth System Model (CESM). 

How does Solar Geoengineering influence tropica cyclones and the tropical circulation? (with Michiel Baatsen and PhD candidate Jasper de Jong)

Typical Solar Geoengieering simulations are performend on model resolutions around 100km, i.e. to rough to capture tropical cyclones. In addition, earlier experiments at IMAU with CESM at higher model resolution have shown that increasing the resolution can reduce some (though not all) model biases. We will be among the first to study the impacts of Solar Geoengineering at a resolution of 25km in the atmosphere and 10km in the ocean. 

The role of Solar Geoengineering in the climate policy mix - exploring scenarios in a simple climate-economy model

Responsible decision-making about Solar Geoengineering depends on many pieces of information we simply do not have yet - its impact on the Gulfstream and tropical cyclones (and many other components of the climate system), the severity of climate change in the absence of Solar Geoengineering, and the future geopolitical situation. A detailed model for optimising Geoengineering deployment (or non-deployment!) therefore does not exist. 

As a rough, very qualitative exploration of future scenarios, we use a very simple climate-economy model called DICE. The model is not suited for detailed, quantitative policy advice, but can be used to explore broad questions like: 

- Is uncertainty of the climate sensitivity (i.e. the how strongly the climate will warm in response CO2) a motivation to develop Geoengineering technologies as "back-up" solution? 

- It is widely feared that the option of Geoengineering reduces willingness to invest in emission reduction. However, can the fear of Geoengineering use also help to "push" regions unwilling to reduce emissions? 

Other research projects

The influence of atmospheric fluctuations on the Gulfstream system (with Femke de Jong from NIOZ and PhD student Aleksandr Fedorov)

Short-term atmospheric fluctuations - in wind, heat flux or precipitation and evaporation - might affect the Atlantic Meridional Overturning Circulation (AMOC, "the Gulfstream system"), both on shorter and longer terms. It has even been suggested that short-term fluctuations caused AMOC collapses in past climate states. Understanding the impact of atmospheric fluctuations on the AMOC might help us to better understand it behaviour under climate change and disentangle signal (collapse) and noise (short-term behaviour) in AMOC measurements. In this project we combine observations (led by NIOZ) and high-resolution modelling (at IMAU). 

See also the project site. 

Agent-based modelling in Economics (and Social Science) 

The DSK model contains an "ecosystem" of interacting firms, banks, labour force, and a government, and is able to generate macroscopic economic behaviour (economic growth, business cycles) form small-scale interactions. It also offers a nice testbed for climate policy. Should a carbon tax start low and increase exponentially, or start higher and remain constant? 

Currently, we are looking at how uncertainty about climate sensitivity (i.e. how strongly the climate reacts to CO2) affects optimal strategy. Should we do more effort in emission reduction if climate sensitivity is high, or at least if we cannot exclude that it is high? Or is climate change so urgent that we need to do our utmost anyway? 

Management and international activities

• Editorial board member at the new journal Oxford Open Climate Change (OOCC)
• Guest editor for a special collection about SRM risk-risk-assessment at OOCC 
• Advisory board member for the Science for Sustainability community at UU