The alternative (burial) impacts the environment considerably as well. There is plenty of land devoted to cemeteries. Trees or metal are used (once) for the casket. In many places, you also need a concrete vault, which would add to the impact.
This page says it's equivalent to a 500 mile drive, which is much more believable: http://www.naturaldeath.org.uk/index.php?page=cremation
That's exactly what I'd want my ashes used for.
In Manhattan, the place that is now Washington Square Park was once the location of mass graves for people who died of yellow fever during an epidemic. Before that, it was used as farmland.
That said, this is far from the norm in the US - New York is one of the few places where this could happen, due to the scarcity of space, and it's also unclear whether people remembered the locations of the graves at the time the park was constructed.
Cemetery land gets reused all of the time. In my city, the main park (1890) and high school (1970) were both built on cemetery land. The land gets seized by eminent domain or purchase, bodies exhumed and rebutted elsewhere.
I'm sorry, but what?
https://en.wikipedia.org/wiki/Lichen
>When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil. While this contribution to weathering is usually benign, it can cause problems for artificial stone structures. For example, there is an ongoing lichen growth problem on Mount Rushmore National Memorial that requires the employment of mountain-climbing conservators to clean the monument.
and
>The lichen exudates, which have powerful chelating capacity, the widespread occurrence of mineral neoformation, particularly metal oxalates, together with the characteristics of weathered substrates, all confirm the significance of lichens as chemical weathering agents.[96]
It's believed lichen may be as old as 2.7 billion years, so they may have beat out every other form of biodegradation by a good margin.
Near where I live, there are boulders that were dragged down a valley by retreating glaciers 10,000 years ago. They've been exposed to the elements for that time, are are materially intact.
That time is a century or more. The US national cemetery (Arlington) is nearly full. Even after 150 year nobody would dare suggest reusing even the oldest plots.
Most US car owners drive at most 10,000 miles a year. A half year's driving? That's only a trivial energy use by 1st and 0th world standards.
Human composting seems like a good idea to me: http://www.nytimes.com/2015/04/14/science/a-project-to-turn-...