Waves of change: how do atmospheric circulation patterns shape our climate?
Understanding atmospheric circulation is key to predicting extreme weather events, yet many uncertainties remain. In EXPECT, Professor Dim Coumou and PhD candidate Rikke Stoffels – researchers at the Vrije Universiteit Amsterdam’s Department of Water & Climate Risk – are working to unravel these complexities and to explore where current climate models might fall short.
As part of the Climate Extremes research group at the IVM, Coumou and Stoffels employ novel data-driven methods coupled with advanced climate models to assess societal risks. A major focus of their research in Amsterdam is understanding atmospheric dynamical changes, also a core theme in EXPECT. Ultimately, the pace of extreme weather intensification hinges on one big unknown:
What’s happening to the jet stream?
What are jet streams?
Jet streams are fast-flowing air currents encircling the Earth from west to east. Each hemisphere has two main jet streams: the polar jet, which is the primary engine of climate variability in the Northern Hemisphere mid-latitudes, and the subtropical jet, closer to the equator.
These high-altitude winds in the upper atmosphere form due to temperature differences between cold polar air and warm tropical air, creating strong pressure gradients that drive air movement.
‘Recent studies which have been published over the last couple of years show there has been a very pronounced wave getting stronger over the last 30 years; this is a continuous trend.’
As Dr Coumou says, his work with EXPECT zeroes in on understanding the forces driving this trend.
Using large-scale climate models to project how regions will fare
Extreme weather events, such as heatwaves, storms, hurricanes, floods, and droughts are becoming more frequent and severe. Decoding how climate change influences these events on a regional scale is a key research pursuit.
‘From a policy perspective, adaptation is always local or regional,’ says Dr Coumou. ‘Societies need good projections of climate change, and the risks associated with that, namely extremes, on a fairly local basis.’
‘Our main task is to identify what’s driving changes in atmospheric circulation,’ explains Rikke Stoffels. ‘We try to uncover the link between what is happening in the tropics and what is happening over Europe.’
How is the Vrije Universiteit Amsterdam involved in EXPECT?
Vrije Universiteit Amsterdam leads Task 3.1 within EXPECT, which centres on:
- Determining the drivers of decadal changes in boreal summer atmospheric circulation.
- Investigating tropical Pacific and Atlantic oceans influences on European weather patterns.
- Evaluating how well climate models capture these large-scale atmospheric changes.
Researchers are studying teleconnections, namely complex links between tropical and mid-latitude areas that influence each other in different ways over short to medium periods of time.
‘Our main task is to identify what’s driving changes in atmospheric circulation,’ explains Rikke Stoffels. ‘We try to uncover the link between what is happening in the tropics and what is happening over Europe.’ To understand the links between changes in climate, researchers are leaning on tools like the Large Ensemble Single Forcing Model Intercomparison Project.
What is LESFMIP? What is its role in EXPECT?
‘LESFMIP is a large ensemble of climate simulations,’ explains Rikke Stoffels. This Large Ensemble Single-Forcing Model Intercomparison Project is a powerful climate modelling framework that helps researchers isolate the effects of different climate forcings.
‘For example, one can take a look at the isolated effect of CO₂ emissions on the climate system and study the changes in the large-scale circulation,’ says Dr Coumou.
Forcings in climate modelling indicate the procedure of changing the boundary conditions of the systems by adding both natural (e.g. volcanoes) and human-made (e.g. CO₂ emissions) drivers of climate change, to simulate how the climate system will respond.
As discussed in a previous interview, forcings are inputs that affect the Earth’s energy balance, used to predict changes in temperature, precipitation, and other climate factors under different scenarios (e.g., increased greenhouse gas emissions, land use changes, or solar variations).
What are the challenges encountered so far?
Simulations, Earth observations, data analysis, machine learning and AI all have the power to guide decision-making across government and industry, notably for the purpose of disaster management.
However, predicting future climate trends remains challenging due to several factors:
- Limited historical data – Modern climate records only span a short time range, making it difficult to identify long-term trends. ‘Our problem is that we have only 50-60 years of observational data on the state of the atmosphere,’ stresses Dr Coumou.
- Natural variability – It is challenging to distinguish between trends driven by global warming and those caused by natural fluctuations.
- Incomplete climate models – Current observations provide only a partial glimpse of what is truly occurring. Models may not fully capture key processes and interactions, leading to uncertainties. Climate models need improvement through enhanced data accuracy, including more precise estimates of past forcings and refined historical observational data.
Looking ahead: what comes next?
In a rapidly warming world, understanding these climate shifts goes beyond science: it’s crucial for future preparedness. The path forward lies in addressing the uncertainties in atmospheric dynamics and EXPECT is at the forefront of this effort.
‘I’m fairly optimistic that in a couple of years’ time, we’ll know a lot more about what’s happening and also about what the models are missing,’ says Dr Coumou. ‘That’s my hope.’
Rikke Stoffels expresses her enthusiasm over the collaborative nature of EXPECT. ‘I think we have a nice international consortium with many people that have different expertise: that’s a great opportunity to learn from each other and achieve scientific goals together.’
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