The summer of 2022 began with historic flooding in Montana, caused by heavy rain and melting snow, tearing up roads and evacuating large areas of Yellowstone National Park.
It ended with a record-breaking heatwave in California and much of the West that strained the power grid and caused blackouts, followed by a tropical storm that set records for rainfall in Southern California. A typhoon swept the Alaskan coast and a hurricane hit Puerto Rico with more than 30 inches of rain.
In between, wildfires raged in California, Arizona and New Mexico against a backdrop of a mega-drought in the US Southwest that was worse than anything the region has experienced in at least 1,200 years. Near Albuquerque, New Mexico, a five-mile stretch of the Rio Grande dried up for the first time in 40 years. Persistent heatwaves continued over many parts of the country, setting temperature records.
Simultaneously, in a five-week period between July and August, five 1000-year rain events occurred in St. Louis, eastern Kentucky, southern Illinois, California’s Death Valley, and Dallas, causing devastating and sometimes fatal flash flooding. Extreme rainfall also caused severe flooding in Mississippi, Virginia and West Virginia.
The United States is hardly alone in its share of climate disasters.
In Pakistan, a record monsoon rain flooded more than a third of the country, killing over 1,500 people. In India and China, prolonged heatwaves and droughts have drained rivers, disrupted power grids and threatened the food security of billions.
In Europe, heat waves sent record-breaking temperatures across Britain and elsewhere, leading to severe droughts and wildfires in many parts of the continent. In South Africa, torrential rain brought flooding and mudslides, killing more than 400 people. Summer may have ended on the calendar, but climate disasters will surely continue.
This is not just an unusual summer: over the years such extreme events have become more frequent and more intense.
Climate change amplifies these disasters
The most recent international climate assessment by the United Nations Intergovernmental Panel on Climate Change found a significant increase in both the frequency and intensity of extreme temperature and precipitation events, leading to more droughts and floods.
A recent study published in the journal Nature found that extreme floods and droughts are becoming deadlier and more expensive, even as the ability to deal with climate risks improves. This is because these extreme events, amplified by climate change, often exceed the planned level of such management strategies.
By definition, extreme events rarely occur. A 100-year flood has a 1% chance of occurring in any given year. So when such events occur with increasing frequency and intensity, they are a clear indication of a changing state of the climate.
The term “global warming” can sometimes be misleading as it seems to indicate that the world will get a little warmer everywhere as people release more heat-trapping greenhouse gases into the atmosphere. What it fails to convey is that warming temperatures are also leading to a more violent world with more extreme climate disasters, as we saw last summer.
Climate models showed these risks were coming
Much of this is well understood and consistently reproduced by climate models.
As the climate warms, a shift in temperature distribution leads to more extremes. The magnitudes of changes at extreme temperatures are often larger than changes in the mean. For example, a 1 degree Celsius increase in mean annual temperature is associated with a 1.2°C to 1.9°C (2.1 Fahrenheit to 3.4°F) increase in annual maximum temperature.
In addition, global warming is causing changes in the vertical profile of the atmosphere and temperature gradients from the equator to the poles, leading to changes in the way the atmosphere and ocean move. The temperature difference between the equator and the poles is the driving force for the global wind. As the polar regions warm much more than the equator, the smaller temperature difference causes global winds to weaken and results in a more meandering jet stream.
Some of these changes can create conditions such as sustained high-pressure systems and atmospheric blockages that favor more frequent and intense heat waves. The heat domes over the southern plains and south in June and west in September are examples of this.
The initial warming can be amplified by positive feedback. For example, warming increases snowmelt, exposing dark soil underneath that absorbs more heat than snow, further increasing warming.
Warming of the atmosphere also increases its ability to hold water vapor, which is a potent greenhouse gas. Therefore, more water vapor in the air leads to more warming. Higher temperatures tend to dry out the soil, and less soil moisture reduces the heat capacity of the soil, making it easier to heat.
These positive feedbacks further intensify the initial warming, leading to more heat extremes. More frequent and prolonged heat waves are driving excessive evaporation, coupled with reduced rainfall in some regions, leading to more severe droughts and more frequent wildfires.
Higher temperatures increase the atmosphere’s ability to hold moisture by about 7% per degree Celsius.
This increased humidity leads to heavier precipitation events. Additionally, storm systems are powered by latent heat, or the large amount of energy released when water vapor condenses into liquid water. Increased moisture levels in the atmosphere also increase the latent heat in storm systems, increasing their intensity. Extremely heavy or prolonged rainfall leads to increased flooding and landslides with devastating social and economic consequences.
While it’s difficult to directly link specific extreme events to climate change, when these seemingly rare events are becoming more common in a warming world, it’s hard to ignore the changing state of our climate.
The new abnormal
So, this past summer could only provide a glimpse into our near future as these extreme climate events become more frequent.
However, to say that this is the new “normal” is misleading. It suggests that we have reached a new stable state, and that is far from the truth.
Without serious efforts to curb greenhouse gas emissions, this trend towards more extreme events will continue. Things are only getting worse, and summers gone by will become the norm in a few years or decades – and eventually it will seem bland, like one of those “beautiful summers” we fondly look back on with nostalgia.
Shuang-Ye Wu, Professor of Geology and Environmental Geosciences, University of Dayton
This article was republished by The Conversation under a Creative Commons license. Read the original article.