Man made deserts

My friend has faith in the unsustainable lifestyle that is so common in big cities and areas of major population. In one of our discussions I heard the statement that bot every desert is man made. Is there any scientific evidence that the deserts of the world are man made? I am particularly wondering about the Sahara, Mojave and the Gobi deserts.

There are many factors that make a desert, but latitude is a big one. Look at a globe and you'll see that there are other deserts that correspond to the Sahara in latitude and that there are corresponding desert areas south of the Equator. Distance from the ocean it's also a major factor. The center of continents are generally drier than the coastal regions. One huge exception to this is the Atacama Desert. It is the world's driest and it borders the coast. There is a narrow band, where fog feeds a plant community. This is also common in other deserts. Prevailing winds are a major factor. The windward side of mountains receives most of the rain. On the big island of Hawaii, there's a spot that gets more rain than anywhere else on Earth. The leeward side is a desert.

Grasslands bordering on the world's deserts, are highly prone to desertification, with human intervention. The Sahel area of Africa and portions of the American West, have been dried out through human activity. Chinese and Russian agriculture have created vast wastelands . The internet is full of information concerning this, so I won't write a book here.

Check out anything on this site or on the Internet concerning Greening the desert. Most of this will involve reclaiming areas destroyed through human activity.

Some deserts are very old, and were certainly not created by humans. It's believed that the Namibian desert is 80 million years old. Older deserts have thousands of species of plants, animals and insects, that are well adapted. Newer deserts tend to have far fewer species.

It would be pretty hard for humans to create all the things necessary to create a true desert as Dale has mentioned, many things have to come together in order to form a desert.

The one thing humans do that does help desertification along is the removal of Old Growth Forest, that changes the climate in many ways.

We are very efficient at killing soil, but that doesn't make it a desert, that just makes it barren dirt.
Even this will be reclaimed by nature once humans are gone from the area.

There are deserts now that used to be covered with trees, once the trees were cut down in clear cut method, the other variables that create deserts were able to do the rest.
One of the best examples would be Lebanon, they used to have great forests of cedar trees but in ancient times there was great demand for Lebanese cedar, now there are none and where the forests were, is desert land.

Most deserts will have areas of Oasis, these can be considered natures greening of the desert.

I don't know about making whole deserts but from my observations I have seen the damage goats do and it looks like desertification. Doing nothing more than fencing an area off in my part of the world gives it a good shot at going green, at least in places. I guess at some point here there were no goats, then man brought them in. I guess before that it was almost all forest, and now its pretty desolate. Lot's of guessing here but I've seen that trees can grow here unaided once established, and I've seen that unfenced, they don't get the chance to become established due to goats.

The Mojave is the product of the rain shadow caused by the Sierra Nevada mountains. California has some of the most extreme and obvious examples of rain shadows in the world. The most popular is probably Death Valley. In less than two hours, you can drive from the town of Lone Pine in the shadow of Mt. Whitney, the highest point in the contiguous United States covered in tens of feet of snow and arrive in Death Valley, the lowest point in North America — one of the hottest and driest places on earth. Man has had no part in the creation of these places. Rain shadows are largely responsible for large deserts. Geology creates geography that alters moisture patterns in the atmosphere, robbing a large area of rainfall, and a desert is born.