Professor Jin-Ho Yoon co-authors Climate Extremes: Patterns and Mechanisms

How does climate change cause more extreme weather and climate phenomena?

This rapidly emerging scientific research field uses "event attribution" to understand the relationship between extreme climate events and climate change. Researchers are identifying physical processes that deepen our understanding of weather phenomena and climate phenomena. The new book published by the American Geophysical Union (including Professor Jin-Ho Yoon of the School of Earth Sciences and Environmental Engineering) summarizes the research on extreme weather and climate so far.

 

Extreme weather / climate events are generally defined as a historical distribution of a given record that is out of the normal range. Sometimes, however, judging the extremes of weather and climate can be as subtle as perceiving human behavior, i.e., I know when something goes wrong, but I do not know the exact cause. Defining extreme weather / climate phenomena under a warming climate should take into account climatology, epidemiology, and geography in addition to the frequency or "return period". Even if events that set new records are intrinsically extreme, there are multiple factors that can make the unrecorded event extremely unusual. For example, a long, humid winter and a rainy spring can cause record floods. Likewise, consecutive droughts can lead to more water depletion than more severe droughts lasting only one season. During California's drought, the precipitation in 2013-2014 was extremely low in winter, and the typical summer dryness has worsened, and the impact of the drought has become worse.

 

Some countries are more vulnerable to certain types of events than others. Depending on climate change, tropical regions are often affected by long-term trends such as stronger rainfall intensity and prolonged long-term drought, such as in Australia. Tropical regions that are habitually in conflict with climate variability are especially vulnerable to problems associated with extreme events because poor families typically use more than half of their monthly income for food and are subject to food instability. Ethiopia and southern Africa in 2017, in the wake of the extreme El Nino from 2015-16, has more than 30 million people in dire need of humanitarian assistance.

 

On the other hand, high latitude regions tend have more types of weather and climate extremes, such as severe regional storms, heat waves, droughts, and floods. The amplified water cycle extremes could be the future climate that many mid-latitude regions face, such as the recent flip-flop of California's drought and flood. Likewise, in spring of 2015, Texas experienced a threefold increase in rainfall during the normal rainy season, resulting in widespread floods, but in 2011 the state suffered significant drought. In the meantime, in 2017, the typical monsoon rainy season in East Asia with 2 feet (600mm) of rainfall in Taiwan within 12 hours and has had catastrophic consequences.

 

We are seeing great diversity in other regions, although extreme weather and climate events are on the rise. If precipitation rapidly increases with air temperature, the effect of natural precipitation becomes even worse. Climate change associated with global-scale phenomena such as El Nino and La Nina appears to be stronger in certain regions (e.g. North America). The increased humidity associated with warming air not only changes the water circulation of the area, but it also affects other areas with atmospheric disruptions. The warming of the Arctic can disrupt the jet stream pattern and cause more wild fluctuations in the weather at mid-latitudes.

 

How predictable are extreme weather and climate conditions?

 

Weather forecasts have matured to the point of using as much information as possible. Climate prediction is rapidly evolving from its early stage. Recent increases in extreme weather provide many predictive opportunities on weekly, seasonal, and multi-year time scales. If the climate system changes more vigorously due to climate change, this energy can be understood and modeled.

 

Where do you need additional data or modeling efforts in this area?

 

More international cooperation focused on coherent climate monitoring leads to improved climate services, which will help us better monitor, understand, and predict the climate extremes. Unfortunately, at a time when we need to know more about how weather and weather patterns change, the world faces a "reporting crisis" because of the rapid decline in the number of weather stations in many parts of the world. Also, important satellite missions were postponed. High-resolution climate modeling and better data fusion techniques are useful for simulating and better predicting climate extremes.