11 October 2023

How heavy is a puffy white cloud? It depends on how big it is.

According to USGS, an average 1 kilometer by 1 kilometer cumulus cloud weighs about 1.1 billion pounds.

Notice that this calculation uses the metric system for the cloud’s dimensions because it’s so much easier to calculate the weight of a cloud using those units.

When the metric system began in France in the 1790s, the units had Earth measurements as their basis. A kilogram was the mass of water in a 10cm x 10cm x 10cm container (a litre). The cloud answer, above, was calculated in metric and expressed in kilograms, then translated to U.S. customary pounds.

Did you know that we use two measuring systems in the U.S.? Everyday things are described in U.S. customary measures (inches, feet, pounds) but, as described in Wikipedia, science, medicine, electronics, the military, automobile production and repair, and international affairs all use the metric system. Also, most packaged consumer goods in the U.S. have to be labeled in both customary and metric units.

All birds are measured in grams and centimeters. I can tell this common yellowthroat is being banded in the U.S. because there are inches on that ruler. But his tail is about 4.5cm.

The U.S. is one of three major countries that do not universally use the metric system.

Why haven’t we completely adopted the metric system?

It comes down to three things: Time, Money and Congress. The change will cost time and money for U.S. industry, and designating an official measurement system requires an act of Congress. Whenever the subject comes up, lobbyists convince Congress to say “No.”

So for now we use two measuring systems.

p.s. Grams and pounds do not measure the same thing at all. Grams are a measure of mass (a fundamental property of matter). Pounds are a measure of force (the force of gravity on a mass).

If your mass is 68 kilograms, you are …
68 kg in Europe
150 pounds in the U.S.,
25 pounds on the Moon and still 68 kg,
0 pounds in outer space and still 68 kg
Your mass is 68 kg everywhere you go.

Read more here in Science News Explores: Explainer: How do mass and weight differ?

(credits are in the captions; click on the captions to see the originals)

18 July 2023

We’ve been paying attention to air quality this summer as Canadian wildfire smoke blows into town. The smoke that reaches us, called smog or soot in the chart below, is labelled PM2.5 by air monitors (the particles are less than 2.5 micrometers in diameter). As you can see there’s a lot of other stuff in the air that the monitors are not analyzing — but they could. In the past few years scientists have discovered that we can check the air for DNA.

In 2020 an environmental DNA (eDNA) study in water led to eDNA studies in the air when a fish inventory compared trawling surveys (shown below) to DNA analysis of seawater samples. Science Magazine reported, “Overall, the team found about a 70% match between species abundance recorded by eDNA and trawls.”

In 2021 Mark Johnson, a graduate student at Texas Tech, realized that pollen and plant fragments are such a big component of air quality that he decided to compare manual plant surveys to eDNA measurements at Texas Tech University’s Native Rangeland.

The two methods complemented each other. Manual surveys detected 80 species while eDNA found 91 using the devices pictured below. According to Science Magazine, “eDNA was better at finding easily overlooked species with small flowers, such as weakleaf bur ragweed. But people were better at spotting plants too rare to release much eDNA, particularly when they had showy flowers, such as the chocolate daisy.”

It was only a matter of time before similar air monitoring was used to detect animals.

Two recent studies — one in the UK, the other in Copenhagen — collected and analyzed air samples for animal DNA. And they found it. To prove their equipment, each study located air samplers near a zoo and both found zoo animal DNA. According to NPR, the Copenhagen study “picked up 49 animal species including rhinos, giraffes and elephants. ‘We even detected the guppy that was living in the pond in the rainforest house.'”

And so we’ve come full circle from detecting fish DNA in water to detecting it in the air.

Read more about the animal eDNA studies at WESA-FM: Scientists vacuum zoo animals’ DNA out of the air.

p.s. There is speculation that this technique could help us inventory endangered species.

(photo credits are in the captions; click on the links to see the originals)

19 June 2023

Compared to the size of our planet we humans aren’t particularly large but with billions of us pumping groundwater we have changed the tilt of the Earth. Slightly.

The angle of Earth’s axial tilt varies over a period of 26,000 years (precession) from 22.1 to 24.5 degrees, but within that it wobbles due to sloshing liquids like molten lava, ocean currents, and massive air currents such as hurricanes.

This very short video shows the North Pole wandering as the axis wobbles.

Earth’s spin axis wobbles, its North Pole tracing out a roughly 10-meter-wide circle every year or so. The center of this wobble also drifts over the long term; lately, it has been tilting in the direction of Iceland by about 9 centimeters per year. …

Now, scientists have found that a significant amount of the polar drift results from human activity: pumping groundwater for drinking and irrigation.

— Science Magazine: Humanity’s groundwater pumping has altered Earth’s tilt

Local water abundance, on the surface and underground, changes a region’s gravitational pull. This principle was used by the GRACE and GRACE-FO satellites as they rode the “hills” and “valleys” of gravity and recorded the presence and absence of groundwater.

To find out what affected Earth’s axial tilt, Clark R. Wilson at the University of Texas at Austin and his colleagues built a model of polar wander factoring in all the sloshing over time, including changes to surface water. But the model was missing something.

When the researchers also put in 2150 gigatons of groundwater that hydrologic models estimate were pumped between 1993 and 2010, the predicted polar motion aligned much more closely with observations. Wilson and his colleagues conclude that the redistribution of that water weight to the world’s oceans has caused Earth’s poles to shift nearly 80 centimeters during that time, reported Thursday in Geophysical Research Letters.

— Science Magazine: Humanity’s groundwater pumping has altered Earth’s tilt

The GRACE satellites detected groundwater changes that produced this map. Notice how groundwater dropped in the U.S. Southeast and the Central Valley of California.

How did we pump so much groundwater? We used machines like these.

Watch the groundwater come and go in India 2002-2008 in this NASA video. (Click on the image to access the video.)

Who knew that we could make the planet move!? 80 cm (31.5″) in just 17 years.

(photos from Wikimedia Commons, maps from NASA, click on the captions to see the originals)