There is a saying that climate is what you expect and time is what you get. In an era of climate change, we can now expect warmer, more extreme weather, and more often than not, that’s what we get. Interestingly, aspects of how Earth’s climate naturally varies around average conditions can sometimes further improve our regional predictive ability.
Scientists and non-scientists alike acknowledge that climate varied widely long before humans began to overwhelm the planet with fossil fuel-driven climate change. Ice ages came and went for well-known reasons, as well as we know why the time of the dinosaurs was much warmer and more inhospitable than today.
Over 100 million years ago, natural processes led to higher levels of atmospheric CO2, just as the burning of fossil fuels is doing now. Higher levels of CO2 during warm periods and lower levels during ice ages tell us that greenhouse gases are a fundamental control knob of Earth’s temperature.
Climate varies naturally on all time scales, from seasons to decades to millions of years, and climate scientists spend a lot of time trying to figure out exactly how and why. This is critical to understanding what might happen next because what we get, season after season, year after year, or decade after decade, will result from natural climate variability interacting with human-caused climate change. Naturally, natural climate variability is also now altered by climate change, which makes climate predictions more complicated.
The year 2022 was unusually disastrous in terms of extreme weather and climate: Australia suffered severe flooding earlier in the year, while India and Pakistan were hit by extreme heat, followed by unprecedented floods in Pakistan. . China and Europe have both struggled with unprecedented heat and drought all summer, just as the Horn of Africa was pushed into a severe humanitarian crisis by its own hot drought. Yet another disaster occurred when Hurricane Fiona hit Puerto Rico and the Dominican Republic. In all of this, the continental United States has experienced multiple extreme heatwaves and endless mega drought for 22 years that is now fueling both wildfires and water crises in the Southwest. One reason for all the climate and weather chaos is obviously climate change. Without climate change, this year’s climatic extremes would have been less severe and extreme heatwaves less frequent.
The footprints of man-made climate change are present in all major climate disasters this year, but in each case climate variability also played a role. Climate change has supercharged extremes that in the past would have been less disastrous. Importantly, one of the main models of climate variability appears to be the main culprit for why we got the climatic extremes where we reached this year: a tropical phenomenon called La Niña.
The events of La Niña are not uncommon: they happen every few years. They are defined by a model of ocean and atmospheric conditions in the tropical Pacific, including colder-than-usual ocean surface temperatures in the central and eastern tropical Pacific. Some are weak or moderate and some are more pronounced. The stronger La Niña, the more likely it is to influence the climate and weather pattern across much of the planet in a recognizable way. The same goes for La Niña’s counterpart, El Niño, during which the tropical Pacific warms up. When a strong El Niño occurs in the tropical Pacific, it can generate a pattern of extreme weather and climate around the world that is roughly the opposite of what a strong La Niña will generate.
Our scientific understanding of how El Niño and La Niña variability works is a valuable tool for predicting what could happen in many parts of the globe months in advance. For example, El Niño events are not only known for a global pattern of extremes that are roughly opposite to La Niña, but are also known to pump large amounts of accumulated heat from the ocean into the atmosphere. The ocean is absorbing most of the heat trapped by increasing concentrations of greenhouse gases in the atmosphere, so we can expect the next strong El Niño to help push global atmospheric temperatures to record levels.
Over the past couple of years, however, it has been La Niña’s natural variability model that has helped produce many of our climatic extremes, only to see climate change supercharging these extremes with a devastating impact. Two consecutive La Nina years are not that unusual, but right now, based on current conditions and sophisticated models, we appear to be on the verge of a rare “three peat” – a third consecutive La Nina year – which will likely last for all of our winter in the Northern Hemisphere.
Persistent conditions in La Niña increase the likelihood of continued heat waves and droughts from Europe and North Africa through the Middle East, northern parts of South Asia and China. Parts of East Africa are also likely to continue to cook and dry out. In other words, the climate disasters that hit each of these places in 2022 could get worse until 2023. And, when it rains, climate change increases the chances that rainfall could be extremely intense.
Closer to home, the consequences of the continued conditions in La Niña are also bad news. We can expect the odds to favor hot, dry weather from southern California through the southern swath of the United States to the southeast. This is typical of La Nina’s past events and predicted by climate models. Despite a relatively rainy summer monsoon in parts of the southwest, we can expect the region’s hot 22-year mega drought to intensify again in its 23rd year. With yet another La Niña on the horizon, this isn’t the year to expect relief.
We cannot stop the natural climate variability and extreme climate that La Niña can bring, so we must instead accelerate our efforts to stop the human-driven climate change that is inexorably turning so many climatic extremes into unprecedented disasters and suffering.
Jonathan Overpeck, Ph.D., is a climate scientist, professor and dean of the School for Environment and Sustainability at the University of Michigan. He has studied drought, climate variability and climate change on five continents. Follow him on Twitter: @GreatLakesPeck