October 24th, 2023
Physical Scientist
Heat waves and cold spells aren’t always as dramatic as other weather events, such as hurricanes and tornadoes, but they can be just as dangerous. Exposure to extreme heat can cause heat exhaustion and heat stroke, and can lead to flare-ups of chronic conditions, including asthma and cardiovascular disease. The CDC estimates that more than 700 people die from extreme heat every year in the U.S., making heat more deadly than any other weather disaster.
Extreme cold, meanwhile, can lead to some of the most dangerous and disruptive winter conditions. It can cause power lines to freeze, roadways to become slick, and can lead to hypothermia and death, particularly in vulnerable populations. In February 2021, for instance, a stretch of record-breaking cold weather in Texas led to burst pipes, icy roads, and power outages, and ultimately claimed the lives of more than 200 people.
Being able to forecast extreme heat and cold events months in advance would be helpful from a public safety standpoint, giving local governments a long lead time to complete the appropriate safety and infrastructure preparations. Thanks to recent research from GFDL, that forecasting ability may soon be possible. GFDL scientists have shown that the SPEAR (Seamless system for Prediction and EArth system Research) model can be used to skillfully predict extreme heat and cold on seasonal timescales.
Cold Extremes
Predicting stretches of colder-than-usual weather is difficult on longer timescales: currently, forecasts for extreme cold are conducted mostly on the daily or weekly scale. Seasonal forecasts, meanwhile, can predict average temperatures months in advance, but not extremes.
A study from earlier this year, however, shows the capability of SPEAR in predicting the frequency of cold days months in advance. The study, published in the journal Climate Dynamics, tested the ability of SPEAR to predict North American cold extremes on a seasonal timescale. It found that SPEAR could skillfully predict extreme cold spells up to nine months in advance in some places.
Liwei Jia, research scientist at NOAA GFDL and lead author of the study, said that making long-range predictions of temperature extremes is challenging because the atmosphere is a chaotic environment, and small changes in the atmosphere can lead to rapidly-shifting weather patterns.
But cold extremes depend heavily on conditions of the land and ocean, making the atmosphere in which their prediction takes place less chaotic. “Because the sea surface temperatures and land conditions vary slowly and are highly predictable on seasonal time scales, this makes it possible to predict cold extremes on seasonal time scales,” Jia said.
Tom Delworth, a senior scientist at GFDL, said that one reason SPEAR is effective at predicting seasonal temperature extremes is the use of a novel approach called “ocean tendency adjustments.”
“This is an approach that reduces the growth of errors in the model ocean, thus keeping model biases relatively small (a bias is the difference between what the model wants to simulate and what we observe in nature),” according to Delworth. “These reduced biases may help to provide more accurate predictions on timescales from a couple of months out to a year or so.”
SPEAR, Delworth noted, also takes the influence of greenhouse gases into account when forecasting extreme temperatures. That, coupled with its focus on the ocean as a main natural driver of climate extremes, may lead to increased realism in SPEAR’s predictions.
For this study, Jia and her colleagues didn’t try to predict exact extreme temperatures; instead, they sought “to predict the frequency of cold days on seasonal time scales from a statistical point of view.”
“Most importantly, we predict the large-scale patterns of extremes which are strongly determined by sea surface temperatures and underlying land conditions,” Jia said. “As long as the sea surface temperatures and land conditions are predictable, the extremes are predictable.”
Heat Extremes
Similar to cold extremes, long-term forecasting of heat extremes is tricky because of the chaotic nature of the atmosphere. But as climate change progresses, bringing with it more heat waves and droughts, it’s becoming more and more critical to be able to predict stretches of hot weather. Heat waves can put a strain on health and emergency services, increase stress on water supplies, and can cause blackouts and power shortages. According to the Intergovernmental Panel on Climate Change, heat waves are likely to get longer, more frequent, and more intense as the planet’s overall temperature rises.
Jia and her colleagues published a study last year that found that, like cold extremes, heat extremes could be predicted several months in advance using SPEAR. “Looking at large-scale patterns on a seasonal average makes it possible to predict extremes at long time scales.” Jia said.
SPEAR specializes in long-term – seasonal to multidecadal – climate predictions and projections. Though it is an experimental model, its findings are used in real-time predictions; its experimental seasonal predictions, for instance, are used as part of NOAA’s North American Multimodel Ensemble for seasonal prediction. Jia said that it’s possible that the study’s method of predicting temperature extremes could one day be used in operational forecasts as well.
Jia and Delworth are continuing to conduct research on the seasonal prediction of climate extremes, including extreme combined weather conditions such as heat and humidity – conditions which can also be dangerous and even deadly.
“We continue to improve our models, moving to higher resolution models that require faster and faster computers,” Delworth said. “We hope that such refined model resolution will allow more realistic simulation of climate and perhaps improved skill in climate prediction and projection of extremes, including hurricanes and extreme rainfall events.”
Learn more about SPEAR, NOAA GFDL’s other earth system models, and how to stay safe in cold and hot weather.