LOS ANGELES — California just recorded its driest January and February on record, sounding the alarm about a third record-breaking drought year.
Across the Pacific Ocean, thousands of people are fleeing record flooding in Australia. Brisbane officials reported 31 inches of rain in six days, and Jonathan Howe, a government meteorologist quoted by The Associated Press, called the amount of rainfall “astronomical”.
Meanwhile, in the eastern Horn of Africa, a prolonged drought raises the frightening specter of starvation for millions of people.
All of these are linked to a multi-year La Niña event, amplified by the effects of climate change, leading to consecutive years of drought in some parts of the world and torrential rains in others.
La Niña is part of a natural cycle in the Pacific Ocean that influences climate worldwide and is often a factor in weather extremes. It is characterized by sea surface temperatures below average in the central and eastern central equatorial Pacific.
Trade winds normally blow from east to west over this region, pushing warm water westward from the Pacific. In the eastern Pacific, near South America, the action of these winds causes cold water to rise from the depths.
The air temperature difference between the east and west of the tropical Pacific sets up a huge cycle called the Walker circulation, in which warm air rises to the west, north of Australia, moves eastward at upper levels of the atmosphere, then cools down near South America. This occurs in the neutral or normal phase, which is up more than half the time.
When a La Niña event takes shape, east-west trade winds strengthen, strengthening the warm water basin in the western Pacific and causing further cooling in the eastern part of the tropical Pacific. The temperature differential between east and west is increased and the Walker circulation is stronger, perpetuating itself through a feedback loop and generally keeping the pattern in place for months or longer.
Precipitation generally decreases over the central and eastern tropical Pacific and increases over the western Pacific, Indonesia and the Philippines. This is because the warmer water in the Western Pacific causes more evaporation, more clouds and more rain, as well as more tropical cyclones or typhoons.
La Niña generally weakens wind shear in the Caribbean and tropical Atlantic, contributing to increased hurricane activity in the Atlantic Basin. Both 2020 and 2021 have been active hurricane seasons, with 2020 being the year with the most named storms of any season on record.
La Niñas is generally associated with colder, stormier than average conditions and increased precipitation in the northern United States, and warmer, drier, and less stormy conditions in the southern parts of the country.
With the exception of an unusually wet December in California, this pattern appears to be unfolding according to script for a second consecutive La Niña year.
The first two months of 2022, typically the wettest of the year, were the driest consecutive January and February on record in the Sierra Nevada, which normally serves as a natural cold storage for California water. Typically, when the snowpack melts in the warm season, it fills state streams and reservoirs, supplying towns and farms.
The brother and opposite of La Niña is El Niño, during which the trade winds from east to west weaken or even reverse. This allows warmer tropical waters to recede eastward toward South America. Walker’s circulation weakens, causing trade winds to decrease.
As with La Niña, this pattern also perpetuates itself in a feedback loop. With warm water now in the eastern tropical Pacific, evaporation and rainfall formation is moving west to east. El Niños often – but not always – lead to wet winters in California.
These are natural climatic variations, but recent droughts, floods and heat waves suggest something has changed.
Human-caused climate change amplifies the effects of natural variations around the world. The United Nations World Meteorological Organization has documented a fivefold increase in weather and climate disasters over the past 50 years.
“That means longer and more intense heat waves, longer-lasting droughts, bigger and more costly wildfires, and more devastating floods, like the ones we’ve seen recently,” said climatologist Bill Patzert. .
According to the Famine Early Warning Systems Network, established in 1985 by the United States Agency for International Development, human-induced warming in the Western Pacific has resulted in a sharp decline in rainfall in East Africa since 1998, and these reductions rainfall is accentuated during La Niña events. .
“The reach of La Niña, enhanced by climate change, is global,” Patzert said. “Drought in California’s Sierra Nevada mirrors two-decade drought in the Horn of Africa.”
While millions of humans face food insecurity or starvation in Africa, warming ocean temperatures are also threatening the largest living structure on the planet, Australia’s 1,400-mile-long Great Barrier Reef. The bleaching, caused by the warming of the ocean, has endangered the reef and its ecosystem.
Global warming increases the evaporative demand of the atmosphere, essentially creating a more thirsty atmosphere. This hotter, drier environment sucks more moisture from plants and soils, reducing streams to drips and reservoirs to empty basins surrounded by bathtubs.
The effect is to intensify droughts, making cyclic drought conditions much more frequent. Vegetation is parched and forests are vulnerable to pests, such as bark beetles, making fire seasons a year-round affair, not just a threat during seasonal periods of dry winds off Santa Ana.
As California and the Southwest fret over the aftermath of a second consecutive rainy season without a show amid the region’s driest 22-year period in 1,200 years, Australia is mobilizing its “army mud “. It was these volunteers who earned this name by helping with the floods of 2011, which was also a La Niña year.
Floods and droughts are two sides of the same La Niña global climate event. But the different faces of the same event are dangerously distorted and exaggerated by the carnival mirror of climate change.
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