Humans can rearrange the shape of our planet almost as easily as the furniture in your living room (or the deck chairs on the Titanic). Of course, it doesn't always work out as planned.
A lot of Earth terraforming is a simple matter of moving water to places where there was no water, and moving land to places that were previously landless. On the surface, this kind of terraforming seems generally beneficial, especially compared to some of the more harmful methods mentioned in part 1.
The earliest artificial islands are Neolithic in origin. Scots were building crannógs 5,000 years ago. These small islands were built up with timber, stone and earth until a stable, round structure suitable for building a house upon was formed. 20th and 21st-century artificial islands are much larger. They can be tourist destinations (Montreal's Île Notre-Dame), urban neighborhoods (San Francisco's Treasure Island), industrial centers (Seattle's Harbor Island), or even entire provinces (Flevoland in the Netherlands). Most of them are constructed using fill dredged from nearby bodies of water or leftover material from construction projects such as grade leveling or tunneling. Île Notre-Dame, for instance, was built from 15 million tons of rock cleared from the digging of the Montreal Metro tunnels.
These kinds of artificial islands are relatively innocuous (I'm sure the level 5 vegans among us can dredge up some objections). U Thant Island isn't really hurting anyone. If you build your fake island on a landfill, however, you've got problems. Landfill islands seem like a win-win. Take tons of garbage and make it into something useful, a nice green island where we can go casino gambling all day long. Unfortunately, chemicals tend to leach out of landfills into nearby groundwater. Plus, landfills are giant methane factories. The vent pipes sticking out are part of our grand experiment to see if we can alter global climate with greenhouse gases.
It's also kind of weird when islands are given symbolic shapes, like the Dubai Waterfront project, which will be shaped like a giant Islamic crescent, or Dubai's Palm Islands, which are clearly alien face huggers. It isn't quite writing your name on the moon with a laser, but it still feels a bit like planetary defacement.
Irrigation is a technology that's tough to talk trash about – human civilization wouldn't have made it very far without it. It's allowed us to settle previously barren areas, and more importantly made crop yields more resistant to short-term rainfall fluctuations. We need irrigation. But just to prove that you really can have too much of a good thing, massive irrigation projects played out over the course of decades have devastating environmental effects. Sometimes we can't see the effects – the Ogallala Aquifer has greatly diminished water levels – but they're still there. Other times the effects are all too obvious. Have you seen the Aral Sea lately? Neither has anyone else. In the 1960s, the Soviet Union started diverting water from the Aral and the rivers that feed it. Today, for all intents and purposes, the Aral Sea no longer exists.
The above NASA image shows the Aral Sea's remnants in 2008, with the sea's approximate 1989 area outlined in blue.
So we can move things around. We can expand our cities with reclaimed land (and there are those greenhouse gases again). We can irrigate deserts. But at human scales, Earth is a closed system. We can drain in decades what took millennia to fill, and there's no easy way to put it back. Consider that the Earth itself is really sturdy. We can add millions of tons of water to an area by creating a reservoir, or build a landmass where there wasn't one, and the planet doesn't really sweat it too much. What happens when we start messing with ecosystems? We'll get to that in part 3.