This Map Shows All the Trees in New York City

Tim Wallace/Descartes Labs
Tim Wallace/Descartes Labs

Trees may not be the first thing that comes to mind when you picture big cities, but they're an essential part of many urban landscapes. By maintaining a healthy tree population, a city can clean the air, provide shade to buildings, and improve the quality of life of its residents.

To quantify the impact trees have, officials first need to keep track of how many grow within city limits—a task that's harder than it sounds. Even with thousands of volunteers working on the ground, tallying all the trees in a city like New York can take years, according to City Lab, and such surveys often don't account for the trees growing in parks or on private property. Using artificial intelligence, researchers at the geospatial analytics startup Descartes Labs have found a way to map all the trees in major cities without taking to the streets.

To make the New York tree map below, Descartes programmed a machine learning model to identify tree canopies from satellite images. This isn't as easy as pinpointing green spots: The program had to be taught to distinguish trees from other greenery, like grass and shrubs, using artificial intelligence. This sets it apart from other tools used to map vegetation like the Normalized Difference Vegetation Index (NDVI), which only accounts for light wavelengths, not height.

Map of New York City's Trees.
Tim Wallace/Descartes Labs

When applied to New York, the tree-mapping technology provides a different view of the city. Some of the most heavily trafficked areas, like downtown Brooklyn and Times Square, are blank spaces on the map. Not surprisingly, parks like Forest Park in Queens and Central Park in Manhattan have the densest concentrations of trees, but some affluent neighborhoods, like the West Village and the Upper East Side, also have plenty of greenery.

New York's vegetation may be impressive by some city's standard, but it's nothing compared to what it was 400 years ago. Here's what Manhattan looked like in 1609.

[h/t City Lab]

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

Two Eco-Minded Kids in England Are Petitioning McDonald’s and Burger King to Nix Plastic Toys

romrodinka/iStock via Getty Images
romrodinka/iStock via Getty Images

Some kids are not content to wait around while the grown-ups sort out the future of our planet. Two of them, 9-year-old Ella and 7-year-old Caitlin, have launched a petition on Change.org requesting that McDonald’s and Burger King stop giving out plastic toys with their kid’s meals, Thrillist reports.

“Children only play with the plastic toys they give us for a few minutes before they get thrown away and harm animals and pollute the sea,” the British girls wrote on Change.org. “We want anything they give us to be sustainable so we can protect the planet for us and for future generations.” The petition has almost 400,000 signatures so far, and their current goal is to reach 500,000.

McDonald's Happy Meal
McDonald's

Last October, UK environment minister Thérèse Coffey also implored McDonald’s to stop giving out plastic toys, suggesting instead that they develop smartphone-friendly games to accompany the meals. At the time, a UK McDonald’s spokesman acknowledged the importance of reducing plastic waste and cited their promise to switch to paper straws, but countered the assumption that the plastic toys were only used for a few minutes, telling The Telegraph that they “provide many more fun-filled hours at home, too.”

The fast food giant did study the environmental effects of their toys last year and found that they are hard to recycle, since they’re manufactured from various types of plastic. As a result, McDonald’s is researching more Earth-friendly ways to make their toys. A Burger King representative told The Wall Street Journal that it, too, is exploring “alternative toy solutions.”

But according to Ella and Caitlin, “It’s not enough to make recyclable plastic toys—big, rich companies shouldn’t be making toys out of plastic at all.” The young activists themselves recycle as much as they can, and even hung a poster in their window about saving the planet.

You can sign their petition here, and learn how to reduce your own environmental impact.

[h/t Thrillist]

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