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Climate change plus a third straight La Niña is not a good thing

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There is an old saying that climate is what you expect, and weather is what you get. In the age of climate change, we can now expect hotter and more extreme weather, and for the most part, that’s what we get. Interestingly, aspects of how Earth’s climate naturally changes around average conditions can sometimes improve our regional predictive skills further.

Scientists and non-scientists alike recognize that the climate has changed on a massive scale long before humans began to flood the planet with climate change caused by fossil fuels. Ice ages came and went for perfectly understandable reasons, just as we know why the time of the dinosaurs was much warmer and inhospitable than today.

More than 100 million years ago, natural processes led to higher levels of carbon dioxide in the atmosphere, just as the burning of fossil fuels is now taking place. High levels of carbon dioxide during warm periods, and low levels during ice ages tell us that greenhouse gases are an essential key to controlling Earth’s temperature.

Climate varies naturally over all time scales, from seasons to decades to millions of years, and climate scientists spend a lot of time trying to understand exactly how and why. This is critical to understanding what might happen next because what we get, season to season, year to year, decade to decade, will result from natural climate variability interacting with human-caused climate change. Of course, even natural weather fluctuations are now altered by climate change, and this makes climate prediction more difficult.

2022 was extraordinarily disastrous in terms of extreme climate and weather: Australia suffered major floods early in the year, while India and Pakistan experienced extreme heat, followed by unprecedented Pakistan floods. Both China and Europe suffered from unprecedented heat and drought throughout the summer, just as the Horn of Africa was pushed into a major humanitarian crisis by a hot drought. However, another disaster unfolded when Hurricane Fiona hit Puerto Rico and the Dominican Republic. Through it all, the mainland United States has experienced multiple extreme heat waves and a massive, never-ending 22-year drought that is now fueling wildfires and water crises in the Southwest. Obviously, one of the causes of all weather and climate chaos is climate change. Without climate change, this year’s extreme weather events would have been less severe, and extreme heat waves less frequent.

The fingerprints of human-caused climate change are present in all of this year’s major climate disasters, but in each case, climate variability has played a role as well. Climate change has exacerbated extremism that would have been less catastrophic in earlier times. Most importantly, one of the main patterns of climate variability appears to be the main cause of extreme weather events where we did this year: a tropical phenomenon called La Niña.

La Niña events are not rare – they happen every few years. They are determined by ocean pattern and atmospheric conditions in the tropical Pacific, including cooler-than-normal surface ocean temperatures in the eastern and central tropical Pacific. Some are weak or moderate, others are more pronounced. The stronger the La Niña, the more likely it is to affect the climate and weather pattern around most of the planet in a recognizable way. The same is true of El Niño, its counterpart in La Niño, where the tropical Pacific Ocean warms up. When a strong El Niño occurs in the tropical Pacific, it can generate a pattern of extreme climate and weather around the world that is roughly the opposite of what a strong La Niña would.

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Our scientific understanding of how El Niño and La Niña variability work is a valuable tool in predicting what might happen in many parts of the world months in advance. For example, El Niño events are not only known to have an extreme global pattern nearly inconsistent with La Niña, but they are also known to pump large amounts of accumulated heat from the ocean into the atmosphere. The ocean absorbs most of the heat trapped by increasing concentrations of greenhouse gases in the atmosphere, so we can expect the next strong El Niño event to help push global atmospheric temperatures to record levels.

However, over the past two years, it has been the natural variation pattern of La Niña that has helped produce many extreme weather events, only to have climate change outweigh these extremes with devastating effect. Two years of La Nina in a row is not unusual, but for now, based on current conditions and evolving models, it appears that we are on the cusp of a rare “three peat” – a third consecutive year of La Nina – likely during the Northern Hemisphere winter .

Persistent La Niña conditions raise the prospect of continued heat waves and droughts all the way from Europe and North Africa through the Middle East, the northern reaches of South Asia, and all the way to China. It is also likely that parts of East Africa will continue to bake and dry. In other words, the climate disasters that hit each of these places in 2022 could worsen through to 2023. And when it rains, climate change increases the chances of precipitation dramatically.

And closer to home, the implications of continued La Niña conditions are bad news, too. We can anticipate that the odds will favor hot, dry weather from southern California through the southern tier of the United States to the southeast. This is typical of past La Nina events and predicted by climate models. Despite a relatively rainy summer monsoon across parts of the Southwest, we can expect the region’s massive 22-year drought to intensify again in its 23rd year. With another phenomenon on the horizon, this is not the year we can expect relief.

We cannot stop the natural climate variability and extreme weather that La Niña can bring about, so we must instead accelerate our efforts to stop the human-driven climate change that is relentlessly turning many extreme weather events into unprecedented catastrophe and suffering.

Jonathan Overbeek, Ph.D., is a climate scientist, professor and dean of the School of Environment and Sustainability at the University of Michigan. He has conducted research on drought, climate variability, and climate change on five continents. Follow him on Twitter: Tweet embed

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