6 Ways Humans Influence the Weather

Girls eat popsicles and cool off in a Tokyo park during a 2014 heat wave. Image credit: Yoshikazu Tsuno/AFP/Getty Images

If you’ve ever spent any length of time on Twitter or talking to friends from northern California, you’ve probably heard a thing or two about humans secretly having the ability to control the weather. While we don’t have the capability to control the weather outside of the movies, we humans and our everyday activities really are able to indirectly influence the weather in ways that go far beyond our addiction to greenhouse gases.

1. CITIES FORM HEAT ISLANDS. 

They’re not exactly wrong when they call the capital of Georgia “Hotlanta.” Most populated areas generate heat simply by existing. The dense web of asphalt roads, concrete sidewalks, brick facades, and tar roofs are able to absorb a significant amount of heat from the daytime sun, even in the dead of winter. This human-made insulation, called the urban heat island effect, keeps city centers a tad hotter on hot days and a little less cool on cold days.

The urban heat island effect is most noticeable during winter storms when air temperatures are hovering right around freezing, putting you right on the line between wet snow, an icy mix, or a cold rain. The artificial warmth from cities can influence the precipitation type in these storms, potentially lowering a city’s snow accumulations compared to its suburbs.

A 2011 study published in the Journal of Applied Meteorology and Climatology [PDF] also found that the urban heat island effect can have a pronounced impact on thunderstorms that form over cities. The researchers studied 91 summertime thunderstorms that formed over Indianapolis, Indiana, and found that their research models could not replicate those thunderstorms without the influence of the urban area beneath the storms.

2. CROPS JACK UP THE HUMIDITY. 

If cities can absorb the heat of the day and make it even hotter, you can imagine how the vast swaths of crops that blanket the countryside can also affect our daily weather. Instead of making it hotter, crops can make a humid day unbearable by sending moisture levels almost off the charts on a putrid summer’s day.

Corn crops are notorious for pushing dew points—the temperature at which the air reaches 100 percent humidity—up above 80°F in the middle of the summer, creating a dangerous heat index that soars far above 100°F. Compare that to a muggy day, which has a dew point around 70°F, or a comfortably dry day with a dew point in the low 50s.

The harvest can have the opposite effect, as seen in northern Oklahoma this summer when farmers harvested their winter wheat crops. The state’s Mesonet, a network of weather stations, found that the newly harvested areas were hotter and had a lower dew point than their cooler but muggier surroundings.

3. PAVING INCREASES THE INTENSITY OF FLOODS.

Vehicles left stranded on a flooded Interstate 45 in Houston, Texas on May 26, 2015. Image credit: Aaron M. Sprecher/AFP/Getty Images 

Our obsession with construction doesn’t stop at influencing temperatures. Paving over porous earth with relatively impervious materials like asphalt and concrete has also had a major impact on flooding during heavy rain events. Fewer places for rainwater to escape means that the sudden influx of water builds up in urban areas or runs off and inundates places that had never seen flooding before.

4. NUCLEAR POWER PLANTS CAN TRIGGER NUCLEAR-EFFECT SNOW.

Lake effect snow is a yearly phenomenon across North America’s Great Lakes, where bitterly cold air flows over the warm lake water, triggering convection that blows ashore as heavy bands of snow. The bands of snow are so intense that communities can see many feet of snow in one day, sometimes accompanied by thunder and lightning.

It’s not only bodies of water that can cause this phenomenon. Nuclear power plants release large amounts of steam during the course of their operations, and on cold mornings when there’s enough moisture in the air, locations immediately downwind of a power plant’s steam stacks can experience “nuclear-effect snow,” which forms through similar means as lake effect snow. The phenomenon isn’t limited to just nuclear power plants, but they produce enough steam that it’s noticeable over a large area. Thankfully for residents nearby, it doesn’t produce much snow—and it’s not radioactive.  

5. URBAN DENSITY CAN AMPLIFY WINDS.  

The robes of Pope Francis are blown over his head by a gust of wind in St. Peter's Square in Vatican City. Image credit: Franco Origlia/Getty Images

If you’ve ever walked down a city street on a windy day, you’ve probably noticed that it sometimes feels like you’re being buffeted by air shot out of an industrial fan instead of a regular windstorm. Dense building construction can amplify the winds and cause gusts to blow much faster than they would out in the open. This wind tunnel effect can cause serious damage, blowing out windows, knocking down trees, and sending dangerous debris hurtling toward the busy streets below.

The principle is the same as holding your thumb over the end of a garden hose to make the water spray out faster—the wind speeds up dramatically as it presses between the buildings. This is also why you should never take shelter underneath a bridge during a tornado. The tornadic winds squeezing underneath the bridge will speed up, increasing the odds that you’ll be pelted by debris or sucked out into the open.

6) JETS CREATE CIRRUS CLOUDS.

The simple act of flying can also create intricate patterns of clouds in the sky that wouldn’t have formed had we not perfected the art of air travel. The hot water vapor produced by the engine exhaust of a high-flying jet aircraft leave contrails, short for condensation trails, in their wake. Contrails can dissipate right away or linger for hours depending on upper-level humidity and winds. These man-made cirrus clouds are most common at high cruising altitudes, but places like Arctic and Antarctic get cold enough that contrails can form at or near ground level. 

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Britain Is in the Midst of a Rare ‘Wind Drought’
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Generating renewable energy in Britain is a little less than a breeze these days: A “wind drought” is halting the country’s wind turbines.

This month’s wind energy output is down 40 percent from the same time last year, New Scientist reports. On average, about 15 percent of Britain’s electricity comes from wind power. Data starting from July 1 of this year put the monthly average closer to 6.9 percent. Last month, turbines were producing less than 2 percent of Britain’s electricity—the lowest output in two years.

That’s with even more wind turbines being installed over the course of the past year, New Scientist says. The data aren’t entirely surprising, though. The jet stream tends to make the UK’s weather drier and calmer during the summer and wetter and stormier during the winter. But the high pressure the jet stream has brought with it this year has been unusually prolonged, scientists say.

“It’s like a lid, it keeps everything still,” UK Met Office spokesperson Grahame Madge told New Scientist. “From the forecast looking out over the next couple of weeks, there doesn’t seem to be any significant change on the way.”

The wind drought shouldn’t cause too many problems in the short term. Electricity demand is low during the summer (very few British homes have air conditioning), and the country’s been able to compensate for the lack of wind by burning more natural gas. If the wind drought continues to persist, though, UK residents may begin to see an increase in utility fees. Natural gas prices have already risen with the increased demand.

“As we continue to transition to a low-carbon energy system, managing the intermittency of renewable power an important role in balancing supply and demand,” a National Grid spokesperson told New Scientist. “However, we have planned for these changes and [are] ready to play our part.”

The wind drought comes about eight years after British politicians vowed to reduce the UK's dependence on fossil fuels. Last year was the first year that electricity generated from low-carbon energy sources like solar power, wind power, and nuclear power outpaced high-carbon energy sources like coal and natural gas. This summer’s wind drought may make it difficult to improve on last year’s numbers.

[h/t New Scientist]

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Drought Reveals Ancient Sites in Scotland That Can Only Be Spotted From the Air
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Typically rainy Scotland is in the middle of an unusually dry summer—and local archaeologists are taking advantage of it. As the BBC reports, the drought has revealed ancient sites, including Roman camps and Iron Age graves, that have been hidden by farm soil for years.

Historic Environment Scotland has been conducting aerial surveys of the country's landscape since the 1930s, but it's in seasons like this, when the crops recede during dry weather, that the buried remains of ancient structures are easiest to spot. Conditions this summer have been the best since 1976 for documenting archaeological sites from the sky.

Aerial view of field.
Historic Environment Scotland

The crescent-shaped crop mark in the photo above indicates a souterrain, or underground passageway, that was built in the Scottish Borders during the Iron Age. The surveyors also found remains of a Roman temporary camp, marked by straight lines in the landscape, built in modern-day Lyne—an area south of Edinburgh already known to have housed a complex of Roman camps and forts.

Aerial view of field.
Historic Environment Scotland

In the image below you'll see four small ditches—three circles and one square—that were likely used as burial sites during the Iron Age. When crops are planted over an ancient ditch, they have more water and nutrients to feed on, which helps them grow taller and greener. Such crops are especially visible during a drought when the surrounding vegetation is sparse and brown.

Aerial view of field.
Historic Environment Scotland

Historic Environment Scotland has a team of aerial surveyors trained to spot the clues: To date, they've discovered more than 9000 archaeological sites from the air. HSE plans to continue scoping out new areas of interest as long as the dry spell lasts.

It's not just in Scotland that long-hidden settlements are coming to light: similar aerial surveys in Wales are finding them too.

[h/t BBC]

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