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Don Paul: Climate and the Southern border crisis

Don Paul: Climate and the Southern border crisis

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Weather – and its sometimes devastating effects – could be a factor in sending people from Central America to the United States.

Many converging crises have led to the surge of migration from Central America to the Southern U.S. border. There is desperation from poverty, hunger, contaminated water supplies and gang violence, creating hopelessness and fear among populations in Guatemala, Honduras and El Salvador. One key factor that receives less frequent mention in news coverage is climate change.

NBC News recently brought the impacts from our warming climate to the forefront in an article on the migration surge. Even as a meteorologist who frequently writes on climate matters, I realized I had not spent enough time looking at these impacts. I’d already found my detailed memories fading concerning the enormous disasters that befell parts of Central America last year from Hurricanes Eta and Iota. Eta, in particular, brought terrible destruction to Honduras last November, in a hyperactive record hurricane year in the Atlantic basin coinciding with the pandemic.

One of the dominant elements in more frequent hurricane landfalls in this region is tied to warmer than normal sea surface temperatures in large parts of the Atlantic, including the Caribbean and Gulf of Mexico. Even now, in mid-April, these warm anomalies are already evident in the Gulf.

Nearly all of the Gulf, large portions of the Southern Caribbean, and the western tropical Atlantic are continuing to run warmer than the averages for sea surface temperatures in the latter 20th century. This extra heat supplies more energy and evaporative moisture to developing tropical cyclones and is a significant ingredient in increased intensity of hurricanes and tropical storms in the region.

Disaster impacts in Central America from such storms receive less media coverage than impacts in North America and the Caribbean. For example, Hurricane Mitch in 1998 became the second deadliest Atlantic hurricane on record, killing more than 11,000 people in Honduras and Nicaragua. The details are startling, but I’d venture a guess many of us have forgotten most of them.

To be unaware of the increasing risk of such catastrophes tied to warming oceans and a warmer atmosphere is also to be unaware that these elements are only going to worsen with time. Human activity continues to be directly linked to these warm anomalies. Greenhouse gas emissions from fossil fuels and agricultural methods will continue to build unless we phase out these technologies. There is no reason to believe warming will slow on a global basis until we do.

In the past, the peak of the Atlantic hurricane season has generally been in later August and September, sometimes into early October. During last year’s extraordinary record season, meteorologist and hurricane expert Philip Klotzbach noted the first 24 named tropical cyclones produced only two major hurricanes (category 3 and up). Four of the last six storms, two in mid-November, were major, with Eta landfalling as a Category 5 and Iota as Category 4. Yes, unprecedented is the correct word for this. There can be no doubt such late-season intensities are tied to the warming climate and sea surface temperatures brought by human activity.

Such devastation results in more than life-threatening hazards. For thousands, these storms become unsurvivable for those without proper shelter. Water treatment plants are destroyed. Access to health care vanishes. Rainfall of up to 30 or more inches, especially in mountainous terrain, produces deadly flash flooding, mudslides and river flooding. Storms like rapidly intensifying Eta and Iota create so much destruction and leave behind calamitous and unlivable conditions in many towns and villages that will endure indefinitely without reconstruction aid.

While an exact duplicate of last year’s all-time record of 30 named storms is statistically unlikely this coming season, the greater likelihood of more major hurricanes will be with us and Central America for a long time to come. The evidence at this point is not tied to more hurricanes in general from warming (though last year such a case could be made for that season), but to more intense hurricanes with rapid intensification more often. The pressure on desperate populations, already facing horrific conditions, will continue to increase.

As for the coming season, one hurricane forecast from Klotzbach and his staff suggests the Atlantic basin will again have above-average tropical cyclone activity. The current La Nina appears to be evolving into a neutral El Nino southern oscillation. With nearly no chance of El Nino conditions developing this summer, the absence of the wind shear El Nino can produce over the Atlantic means more favorable conditions for tropical waves to evolve into cyclones. (El Nino actually can lessen activity in the Atlantic basin due to strengthened winds aloft that can shear the circulation in tropical systems.)

Klotzbach’s research group at Colorado State University notes the absence of El Nino favors above-average activity, but their prediction of 17 named storms and eight hurricanes is down considerably from what occurred last year. One hopeful factor is the SST anomalies farther east in the tropical Atlantic are smaller than what was evident last year. Klotzbach’s forecast last year, however, even after it was updated as evidence mounted favoring an extraordinary season, fell shy of the mark in several categories.

Hurricane outlooks early in the season are a very difficult and inexact call at best. As of now, there is little reason to believe this will be a quiet year in the Atlantic basin. How Central America will fare is impossible to know in mid-April, but what is known is the destruction still in place from last autumn remains catastrophic for hundreds of thousands of people.

In future decades, what’s called the Atlantic multidecadal oscillation, which is at least partly detached from climate change, may shift back to a phase that would lower the overall frequency of Atlantic hurricanes to some extent.

Still, with the accelerated warming now underway, it’s problematical whether that less-active phase will have the kind of impact it had in a cooler era. Even if hurricane frequency begins to fall back, the ratio of major hurricanes to less intense hurricanes might still be at an elevated stage with warmer oceans. Whatever the case, the migration pressures from climate and weather-related catastrophes will not be fading in the foreseeable future.

Allergy experts say rising temperatures and air pollution have led to longer growing seasons that start earlier.

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