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Press release | News | Focus | Climate | Environment
Warmer winter temperatures brought forward the growing season, leaving crops more vulnerable to frost Between 6 and 8 April 2021 an intense late frost episode damaged agricultural lands in France. Vineyards in particular were severely affected, with early assessments estimating losses of almost 2 billion euros. The cold wave hit France after the country experienced record high temperatures in March.
Now, a group of researchers has quantified the role that human-caused climate change played in the event. Their analysis focused on an area in central France well known for its grapevines, encompassing Champagne, the Loire Valley and Burgundy. The results show that while global warming made the cold wave less likely, it also made bud burst happen earlier in the year. During the bud burst stage, vineyards are especially susceptible to frosts. The researchers concluded that overall, human-caused climate change made the damaging frost event about 60% more likely.
Nicolas Viovy, Senior scientist at the Atomic Energy and alternative energies Commission (CEA) and the Institut Pierre-Simon Laplace, said:
Global warming is affecting the way plants and animals behave. Understanding these changes is critical to protect our biodiversity and build resilient food systems.”
If climate change gets worse, these changes will worsen too. This will create challenges for farmers, the wine industry, and wine lovers everywhere.”
The research is part of the World Weather Attribution initiative and was conducted by an
international group of scientists from the Institut Pierre-Simon Laplace (from the French
National Centre for Scientific Research and the Alternative Energies and Atomic Energy
Commission), the Royal Netherlands Meteorological Institute, the University of Oxford, the
Max Planck Institute for Biogeochemistry Jena, and Météo-France.
To evaluate and quantify the effect of climate change, the researchers compared climate
models that include human-caused global warming with those that don’t include it.
These models show that climate change made the 2021 April cold wave less likely. The
lowest temperatures between April and July have increased by 1.2ºC in the region studied
due to human-caused climate change. And cold frost episodes, which would happen once
every 10 years without climate change, now have a return period of approximately 160
years.But because winters are now warmer, the growing season is happening earlier in the year,
exposing the vines to lower temperatures.
This was estimated using a metric called Growing
Degree Days (GDD), which is commonly used by farmers to measure the maturity of their
crops. GDD is obtained by adding daily average temperatures. It reflects how much heat has
been accumulated by the plants throughout the growing season and can be used to estimate
Optimal GDDs for each growth stage vary amongst species and strains.
A typical GDD value for the beginning of the growing season in the region studied sits
between 250°C to 350°C.
When the researchers calculated the minimum temperatures in place when GDD crosses
the 250ºC threshold, they observed they had decreased by an average of 2.0ºC due to
climate change. The period when GDD is between 250ºC and 350ºC is also cooler now, with
minimum temperatures also on average 2.0ºC lower.
So while temperatures have overall increased over the last decades, GDD values show that
crops are maturing earlier in the year, leaving them more exposed and vulnerable to low
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.