Climate Blind Spots: The Threat of Compounding Weather Events
You saw it here, first, of course – but now researcher Kai Kornhuber, who I’ve been following since I interviewed him at the American Geophysical Union some years ago, has a new paper about the potential impacts of “co-occurring”, simultaneous, climate extremes.
Covid taught us all about the importance of global supply chains. We are going to learn a whole lot more.
Weather and climate extremes, such as prolonged drought, heavy rainfall and heatwaves, can lead to harvest failures. These are occurring with increased magnitude and frequency on a warming planet.
In addition, such events can disrupt supply chains, decreasing food supply and leading to price spikes.
Our previous work shows that when extreme weather events happen simultaneously – such as a heatwave and drought at the same time – this can negatively affect crop yields in major crop-producing regions, known as “breadbaskets”.
This co-occurrence constitutes a growing food security risk.
In our latest paper, published in Nature Communications, we highlight factors that can lead to low crop yields in several breadbasket regions simultaneously. We also examine how well state-of-the-art climate and crop models are able to reproduce observed relationships.
We find that climate models tend to underestimate the risks of concurrent extreme weather events, potentially leading to “blind spots” in our understanding of future implications.
Ensuring global food security under changing climate conditions is a global challenge.
Meeting this challenge relies on reliable projections of future climate conditions, in order to establish reasonable and preventive adaptation measures.
Such assessments are not trivial. They rely on “coupled” experiments that combine both climate models and crop models. The projections must also be done for a range of emissions scenarios in order to fully understand the risk.
Climate extremes are rare, but impactful, events. The accuracy with which we can determine future climate risks for agriculture depends on the skill of climate models in accurately reproducing their frequency and magnitude, as well as the crop models’ accuracy in simulating crop responses.
Research shows that increasingly complex climate risks, in which several extremes interact, are a direct consequence of rising extreme weather trends.
More and longer-lasting extremes translate to higher likelihoods of consecutive climate disasters.
For example, two hurricanes in a row hitting the same region; several different disasters occurring at the same place at the same time, such as concurrent heatwaves and drought; or multiple disasters occurring at the same time globally, such as heatwaves in multiple regions.
Such “compound” events are usually associated with greater impacts, often beyond the sum of the effects had each disaster occurred in isolation. Interacting effects put extra stress on existing vulnerability, disaster preparedness and disaster response measures.
For instance, heatwaves are particularly disastrous for local crop production if they occur in unison with intense drought conditions. Consecutive heatwaves in a region can cause crops to fail that might have survived a solo event.
‘Breadbaskets’
From a global food security perspective, simultaneous extremes are particularly problematic as they could lead to harvest failures in several crop-producing regions – known as “breadbaskets” – at the same time.
As a result, countries that rely heavily on crop imports could experience heightened food insecurity, as global scarcity could lead to price spikes and even result in national export bans.
Major crop-producing regions, known as “breadbaskets”, in the midlatitudes (green shading) and an illustration of the jet stream in one of its preferred positions (purple lines). Hatched regions are areas affected by warm (red) and cold (blue) anomalies. Credit: Kai Kornhuber
Many breadbasket regions, such as central North America, western and eastern Europe and Asia, are located in the temperate climate zones of the mid-latitudes. In these regions, weather patterns are controlled by the jet stream, a current of fast-flowing air that encircles the globe.
The important role of the jet stream in driving extreme weather conditions has been illustrated by some of the most extraordinary climate events of the past few years.
In 2021, the record-shattering “heat dome” in the Pacific north-west that fuelled wildfires and caused hundreds of deaths was directly linked to an intense “ridge” in the jet stream. This caused a high-pressure system to linger over the region. Likewise, the record-breaking heatwaves in Europe in 2018 and 2019 were associated with a meandering, wavy jet stream.
Often, these meanders – also referred to as Rossby waves – expand over larger parts of the globe, promoting extremes in several regions at the same time. In 2022, during the northern hemisphere summer, a strongly meandering jet led to synchronised extremes in the US, Europe and China. Media outlets at the time were quick to point out the links between the heatwaves.
The map below shows surface temperature anomalies across the northern hemisphere during the week of 18 July 2022, with red indicating higher than average temperatures. The concurrence of the five heatwaves – marked with circles – was caused by the meandering jet stream.
Surface temperature anomalies for the week commencing 18 July 2022, with red indicating higher temperatures. The five circled regions are places experiencing higher than normal temperatures concurrently, due to meanders in the jet stream. Credit: UK Met Office (2022)
Our previous work has shown that certain jet stream patterns can not only enhance the concurrence of extreme weather events, but also negatively affect crop yields in major breadbasket regions.
In our latest paper, we show that summers with strongly meandering jet stream patterns favour the co-occurrence of low crop yields in several pairs of major crop-producing regions, increasing the probability of such events by a factor of three in some regions. This constitutes a risk for food security.
Simultaneous harvest failures across major crop-producing regions are a threat to global food security. Concurrent weather extremes driven by a strongly meandering jet stream could trigger such events, but so far this has not been quantified. Specifically, the ability of state-of-the art crop and climate models to adequately reproduce such high impact events is a crucial component for estimating risks to global food security. Here we find an increased likelihood of concurrent low yields during summers featuring meandering jets in observations and models. While climate models accurately simulate atmospheric patterns, associated surface weather anomalies and negative effects on crop responses are mostly underestimated in bias-adjusted simulations. Given the identified model biases, future assessments of regional and concurrent crop losses from meandering jet states remain highly uncertain. Our results suggest that model-blind spots for such high-impact but deeply-uncertain hazards have to be anticipated and accounted for in meaningful climate risk assessments.
