What if Earth had no deserts?

Deserts are dry, dry, dry. Very little rain falls there.

Some deserts are sandy. Some are rocky. Some are even cold! What if there were none?

Picture a desert and you might imagine endless sand dunes under a blazing sun. But the U.S. Geological Survey points out that deserts can be hot or cold, sandy or rocky. The one thing they always share is that they are dry.

About a third of Earth's land is desert. So what if there were no deserts at all? Would Earth just be greener? Or would we lose something important? This thought experiment follows three paths: where deserts come from, desert animals, and desert dust.

USGS defines deserts by dryness, not heat: arid land with meager rainfall and sparse vegetation. In Peveril Meigs's widely used 1953 scheme, arid lands receive under 250 mm of rain a year and extremely arid lands go at least 12 consecutive months without rain.

This lab asks what Earth would be like without them, and what that would even require. Facts come from USGS, NOAA, NASA and zoo scientists; consequences are reasoned ideas.

Many deserts sit in two belts around Earth, north and south of the middle.

There, dry air sinks down from high up. So clouds and rain are rare.

Deserts are not scattered randomly. NOAA explains that air rises near the Equator and flows toward the poles high up, and that a belt of high pressure sits at about 30 degrees north and south. In high pressure the air sinks, and sinking air warms and dries out, so clouds melt away and rain is rare. Look at a globe and you'll find many deserts near those lines, including the American Southwest, northern Africa and Australia.

Other deserts form behind tall mountains, which squeeze the rain out of the air before it reaches the far side. That's called a rain shadow.

NOAA's three-cell model places a surface high-pressure band near 30° N/S, and NOAA explains that sinking air warms and evaporates clouds, which is why fair, dry weather accompanies high pressure. Many deserts lie along these latitudes.

USGS classifies deserts as trade wind, midlatitude, rain shadow, coastal, monsoon and polar. Trade-wind deserts such as the Sahara lie where dry trade winds clear the clouds; rain shadows form in the lee of mountains; coastal deserts such as the Atacama sit beside cold ocean currents. Polar deserts cover nearly 5 million km².

In our pretend world, every desert gets plenty of rain.

What would happen to camels and foxes? And to faraway forests?

In our pretend world, every desert suddenly gets enough rain to stop being a desert. That's a huge change: it would mean the air no longer sank and dried out near 30 degrees, and mountains no longer blocked rain.

Follow the paths in the lab: where deserts come from, the animals that live there, and the desert dust that feeds a rainforest far away. Each card says whether it's a fact or an idea.

Eliminating deserts is not a local change. It would require a different global circulation, without subtropical subsidence, and different relationships between mountains, ocean currents and moisture. The scenario therefore treats 'no deserts' as a premise and follows its consequences for ecosystems and nutrient transport, labeled as ideas.

Desert animals are special. Fennec foxes have giant ears that help them stay cool.

Camels can go a long time without drinking water.

Deserts are home to animals with amazing tricks. Fennec foxes, the smallest members of the dog family, have the biggest ears for their size of any of their relatives; the ears let heat escape and help them hear prey under the sand. They can go a long time without drinking, getting water from their food.

A camel can go a week or more without water and then drink up to 145 liters at once. Its hump stores fat, not water. Without deserts, animals like these might lose the homes they're suited to.

The Smithsonian's National Zoo describes fennec foxes as the smallest canids, with the largest ears relative to body size in the family, used to shed heat and locate prey beneath sand; furred paws grip sand and insulate against hot ground, and they hydrate largely from food.

San Diego Zoo Wildlife Alliance notes that camels can survive a 40 percent weight loss and then drink up to 145 liters in one session; humps store fat as an energy reserve. USGS adds that deserts' dryness makes them ideal for preserving fossils and human artifacts.

Wind lifts dust from the Sahara Desert. It flies across the ocean!

Some lands in the Amazon rainforest. The dust has food for plants in it.

Here is one of the most surprising links on Earth. A NASA satellite called CALIPSO measured dust blowing out of the Sahara Desert from 2007 to 2013. On average, about 182 million tons left the Sahara each year, and about 27.7 million tons landed on the Amazon rainforest across the Atlantic Ocean.

That dust carries phosphorus, a nutrient that works like fertilizer. Scientists estimate it brings the Amazon about 22,000 tons of phosphorus a year, about as much as the rainforest loses to rain and floods.

NASA's CALIPSO lidar data (2007–2013), analyzed by a team led by Hongbin Yu, show winds lifting an average 182 million tons of dust a year past 15° W; 132 million tons remain aloft near 35° W, 27.7 million tons deposit over the Amazon basin and about 43 million tons continue past 75° W toward the Caribbean.

Using phosphorus fractions from dust sampled at the Bodélé Depression, Barbados and Miami, the team estimated about 22,000 tons of phosphorus delivered to the Amazon each year, roughly matching losses to rain and flooding.