A new study from Stanford University shows that the type of heat, a dry condition that can shrink yields, shake food prices and lay the foundation for forest fires that destroy more and more areas simultaneously as a result of climate warming.
According to researchers, climate change has doubled the possibility that an area will experience a warm and dry year compared to the average for that place during the mid-20th century. It also becomes more likely that dry and very warm conditions will reach major agricultural areas in the same year, potentially making it more difficult to surplus in one location to make up for low yields elsewhere.
"When we look at historical data in key areas and grazing, we find that before anthropogenic climate change, there was a very low possibility that every two regions would experience very severe conditions simultaneously," said climate scientist Noah Diffenbaugh, Kara J. Foundation professor at the Stanford School of Earth, Energy & Environmental Sciences (Stanford Earth) and senior author of the study published November 28 at Progress of Science. The study is titled "Multi-dimensional risk in a non-stationary climate: the combined probability of increasingly warm and dry conditions."
"The global market provides a hedge against local extremes, but we have seen climate buffer erosion as an extreme increase in response to global warming," said Diffenbaugh, who is also a senior member of the Kimmelman Family at the Stanford Woods Institute. for the Environment.
The new study shows a future where some regions risk experiencing low yields simultaneously. That's because, while some plants can thrive in the warm growing season, others – especially seeds – grow and mature too quickly when temperatures rise, dry days continue to accumulate and warmth lasts overnight. As a result, hot-dry conditions tend to produce smaller harvests than main commodities, including wheat, rice, corn and soybeans.
The implications go beyond agriculture. The same hot and dry conditions can also exacerbate the risk of fire, drain vegetation in the summer and autumn and trigger wildfires that spread very fast like those that burned more than 240,000 acres in California in November 2018.
Move the target
The basic trend of global warming – 1 degree Celsius or 1.8 degrees Fahrenheit since the end of the 19th century – provides an intuitive logic to the core findings of the study. "If it gets hotter everywhere, it's likely to get hot in two places at once," Diffenbaugh explained, "and it might also be hotter when it's also dry in two places at once."
However, despite that simple intuition, accounting for ongoing changes and interdependence on rainfall and temperature in different locations through time presents statistical challenges. As a result, many past analyzes see warm and dry events as independent phenomena, or in various regions as independent of each other.
That approach might underestimate additional risks due to human-caused global warming, as well as the social, ecological and economic benefits of emission decomposition. "When this extreme occurs simultaneously, it exacerbates the adverse effects beyond what one of them will cause separately," said Ali Sarhadi, lead author of the study and postdoctoral scholar at Diffenbaugh's Climate and Earth System Dynamics Group at Stanford Earth.
Extreme becomes normal
The new study uses historical data from the past century to measure the chance that different regions experience hot and dry conditions in the same year. Analysis shows that before 1980, there was a less than 5 percent chance that two regional couples would experience extreme temperatures in a year which were also dry in both regions. However, in the past two decades, opportunities have increased by 20 percent for some regional couples.
For example, the opportunity that China and India – the two largest agricultural producers in the world and the two most populous countries – both experienced low rainfall and very warm temperatures in the same year had been reduced from less than 5 percent before 1980 to more than 15 percent a day this, Diffenbaugh said. "So what was once a rare event can now be expected to occur with some order, and we have very strong evidence that global warming is the cause."
In addition to their analysis of historical data, the authors also analyzed projections of possible climate models for future global warming scenarios. They found that in decades, if the world continued on the current trajectory of emissions, the chance that average temperatures would rise far exceeded the range normally experienced in the mid-20th century which could rise by 75 percent in many regions.
But achieving the goals outlined in the Paris United Nations climate agreement is likely to substantially reduce those risks, Sarhadi said. While the White House has announced its intention to withdraw the United States from the agreement, the study shows that achieving emissions reduction targets in a 200-country pact will allow the world to dramatically reduce the possibility of combining the hot and dry conditions that afflict some agricultural land. around the world. "There are still options to reduce this change," he said.
Planning real risks
The framework built for this study is an important step in outlining the risks associated with some extreme climates that come together in one region, where they can often be united together. What are the possibilities, for example, high temperatures, strong winds, and low humidity combined to create a great fire condition in the past, and how do opportunities change as a result of global warming? That is the type of question that can be answered by the team framework. This is a very urgent matter for officials who are now counting on the historic scale and intensity of fire in California.
"Many events emphasize infrastructure, and our disaster prevention and response systems occur when some materials come together in the same place at the same time," Diffenbaugh said. High storm waves and the speed of wind with heavy rain can make the difference between passing storms and tropical storms that cause disasters; Wind patterns and humidity levels in various parts of the atmosphere affect the severity of rainstorms and associated flood risk.
The main challenge for decision makers is to understand what is expected in climate change. That means sharpening shared opportunities, which are at the core of the calculations made by engineers, policy makers, humanitarian aid providers and insurance providers to allocate resources, establish building codes and design other evacuation and disaster response plans.
"People make practical decisions based on the probability of various combinations of conditions," Diffenbaugh said. "The standard is to use historical probabilities, but our research shows that assuming that historical probabilities will continue into the future do not accurately reflect current or future risks."