In 1985, a passenger jet landing at DFW airport was forced to the ground by an unusual downward blast of wind called a downburst. The plane struck cars on the highway and a water tank, then crashed on the airfield, killing more than 100 people.

It was the third such fatal crash in a decade. So, the FAA set out to invent a new warning system for these dangerous wind events. A downburst is a sinking column of air within a thunder cloud that accelerates toward Earth, reaching speeds over 100 miles an hour.

When it strikes the ground, it blasts out in all directions, like a mammoth version of water splashing in a sink. These winds are strongest just 10 to 30 feet from the ground and travel horizontally outward in all directions. They can fell trees like a tornado’s whirling winds, but they all fall in the same direction, like dominoes.

For aviation, the first step was training pilots to look for visual signs – expanding rings of dust on the ground below, or sharply defined shafts of intense rain.

Technologically things were more complex. Vulnerable airports installed a network of wind sensors, as well as advanced Doppler radar that could track wind speeds. All fed into an early alert system.

By 1994, 46 high traffic airports had installed these systems. They haven’t had a single downburst accident since -- and technology continues to improve. A triumph of aviation safety.

Sand is incredibly common. There are oceans of it – in oceans, and deserts too. But, for our purposes, that’s not the right kind of sand.

We use sand in concrete, to make bridges and roads, buildings, houses and power plants. We use it in glassmaking, for windows, computer chips, solar panels and much more. We use it for hydraulic fracturing, to prop open cracks in shale deposits so oil and gas can flow.

In all, we use billions of tons of sand every year. But only a certain kind will do.

Beach sand is often mixed with salt. If used in concrete, it can corrode the reinforcing steel. And the grains of beach sand, and especially desert sand, are often rounded by waves or wind. Concrete needs angular grains that lock together. Hydraulic fracturing needs hard grains that can withstand pressure. And glassmaking needs almost pure quartz.

That means, for most uses, the ideal sand is angular, well-sorted quartz. And that’s only found in a few places.

Rivers and streams are natural sorting machines. They break down and wash out weaker minerals, leaving quartz sand in bars and banks, which can be dredged or mined. Through time, many of these quartz sand deposits were lithified into sandstone, which today can be ground back into sand.

Our demand is so great that this once common material is becoming scarce, spawning a lucrative international trade -- for the right kind of sand.

Plastic has remarkable value to humans. But it’s also a major source of ocean plastic pollution.

Most of it is nets and rope from fishing boats, or municipal garbage that’s carried down rivers into the ocean. There it accumulates in spinning gyres of plastic, twice the size of Texas.

Large pieces eventually break down into fragments and microplastics. But because plastic is made to be durable, it won’t degrade any farther than that.

Wouldn’t it be great if we could clean it up?

That’s what a Dutch teenager thought when he was diving in Greece and saw more plastic bags than fish. He created a high school science project -- that has since grown into an international nonprofit, called The Ocean Cleanup, employing engineers, marine biologists and collection teams.

They set up huge U-shaped nets that float with the current in the spinning gyres, in the top few feet of water where most plastics (but few fish) are. These gradually capture the debris, which their boats collect and haul to shore.

They’ve also installed collection systems at the mouths of rivers to intercept plastic before it enters the ocean. Together, their systems have captured millions of pounds of plastic waste, which they sort, recycle or properly landfill.

There’s much more to do, but they’ve inspired governments and other nonprofits to work on plastic waste management on land and at sea.

Hopefully, with growing awareness, we can all make a meaningful difference in ocean plastic pollution.

In the mid-1800s, London’s SoHo neighborhood was a terrible smelling place to live, as raw sewage ran through the gutters into open cesspools.

When a cholera epidemic broke out, 600 people died and many remaining residents fled, fearing – as was common then – that foul air spread the disease.

Local physician John Snow didn’t buy it. Ten years earlier, he had proposed that cholera spread through contaminated water. But lacking proof, he was ignored.

With an outbreak on his doorstep, he saw an opportunity to test his hypothesis – and save his neighborhood.

First, he obtained the addresses of every person who had died. Then he walked the streets plotting the deaths, and everything else, on a map.

Soon a pattern emerged. Most of the cases clustered around one public water well.

He began interviewing area residents. Locals with their own private wells had not gotten sick. Workers at a nearby pub, who drank a daily ration of beer instead of pump water, were also spared.

Snow convinced local authorities that water from the well was to blame, and persuaded them to remove the pump handle, forcing residents to draw their water elsewhere. Immediately the cholera outbreak ended.

With his cholera map, Snow had begun the field of evidence-based epidemiology. This was well before germ theory and microscopes could identify the true culprit, the cholera bacteria, that had spread through sewage leaking into the water supply.

Before modern energy gave us modern air conditioning, we had sweat to keep us cool. And shade. And maybe a jump in a lake.

Animals still rely on those today to beat the heat. Horses, like humans, sweat. When the sweat evaporates, it cools the skin. Dogs, antelopes and some birds pant, drawing breath rapidly across their tongues and throats, where evaporative cooling brings down the temperature of blood near the skin surface. Other birds vibrate the flaps of skin on their throats to circulate air around blood vessels found there.

Elephants do something similar, cooling blood vessels in their huge ears, by flapping them. Camels and toucans draw air across blood vessels in their noses. Rodents and amphibians burrow in the soil or under leaf litter, where it’s cooler and moister.

Some toads burrow and go dormant until the next rain comes. Some even form a protective cocoon of their own shed skin. Deer, doves and many other creatures seek shade during the heat of the day, resting silently to keep metabolic rates low. Even fish seek shade underwater, under overhanging rocks or docks. Or they retreat to the dark depths, where the water’s cooler.

Speaking of water, buffalo and birds splash in shallow pools. Vultures, maybe not surprisingly, go so far as to pee on their own legs to cool themselves off. Which just goes to show, when the heat rises, animals have found amazing ways to adapt.

If you’ve been on a boat, pretty much anywhere in the tropics, you’ve seen mangrove forests.

There are at least 75 species of these small trees, evolved to live in harsh tidal conditions, their roots in sand, their trunks often submerged in saltwater.

There, they can form dense thickets that protect the coast from ravaging waves and storm surges. And that’s just one of their benefits.

Mangroves’ arching root networks trap and stabilize sediment to help build up the coast. In the process, they filter and clean coastal water.

Those same roots serve as nurseries, sheltering the young of many fish and crustacean species. While the forests provide timber for local human populations, and store carbon.

But mangroves are in peril -- from coastal development, agriculture, and especially aquaculture.

Shrimp farmers in Asia are responsible for a third of global mangrove destruction, as they clear forests to build their ponds.

Early efforts to replant the forests had failed. Until an innovative Florida ecologist realized that mangroves thrive best when their roots are wet only 30% of the time and dry the rest, as the tide comes and goes.

He used a backhoe to regrade the coastline to encourage those conditions. Within three years, the resilient mangroves had returned. His methods proved so successful, they’ve been adopted globally, in a preservation program that intends to bring 20% of mangrove coverage back within the decade.

On another episode, we told you about urban heat islands. Buildings and asphalt absorb summer heat -- from sun and air, cars and trucks, power plants and air conditioning -- and hold it, driving city temperatures far higher than surrounding areas, sometimes to devastating effect.

Urban heat islands have killed thousands. But new studies of over 3,000 cities around the world show they’ve saved many more! That’s because heat islands also hold heat in winter, as buildings, transportation and industry ‘leak’ heat into the environment.

The result, just as in summer, is that cities can be 10 degrees Fahrenheit warmer. That means less energy required for heating homes and buildings. And, it means many fewer deaths from hypothermia, heart attacks and respiratory illness.

The studies show that, in the global average, urban heat islands saved four times as many lives in the winter as were lost in the summer. In cold climates, it was 11 times as many!

Tropical cities may not enjoy these benefits – since their winters are not cold enough to kill. But overall, this suggests city planners should adapt regionally to urban heat islands.

Warmer cities should try to mitigate heat effects... while colder cities may want to encourage them!

Cities that experience both temperature extremes – and many do – may investigate changing roof colors and other flexible solutions that could reflect heat in summer, and absorb it in the winter. Changing, like nature, with the season.

Summer in the city. It’s sweltering. The sun beats down all day. Its heat is absorbed by concrete buildings and blacktop, which hold that heat at night -- and into the next day.

The heat builds over weeks and months, keeping summer city temperatures much higher than their surrounding suburban and rural areas. Cities can be 10 degrees Fahrenheit hotter, or more!

That’s what’s called an urban heat island.

People respond by turning down the thermostat on their air conditioning. Exhaust from AC units and heat from nearby power plants further warm the air.

The increased electric load can lead to brownouts, or blackouts. And if people lose power, and air conditioning – or if they don’t have it to begin with – the high urban temps can be deadly.

Thousands of people in normally temperate cities in Europe and Asia have died over the past years in summer urban heat waves.

So, city planners are working to cool these heat islands. Methods can include so-called ‘cool roofs,’ which use white paint or reflective materials to radiate the sun’s heat, rather than absorb it.

Cool roofs can reduce indoor building temperatures by a few degrees Fahrenheit. Green roofs, planted with gardens or even trees, can double that reduction.

Likewise, creating more urban green space cools cities, as plants give off water vapor to provide evaporative cooling to their leaves, and the air.

Remarkably though, these deadly heat islands may save more lives than they’re endangering – and we’ll talk about that on another EarthDate.