Of course there's cremation, which is popular here and in Japan, but even with efficient new cremators, it's not an environmentally-friendly option. Other new methods of disposal include bio-cremation and freeze-drying, but they still use energy, which is also is increasingly short supply.
Dealing with the problem of burial space shortages means dealing with death and with the population problem; two subjects that most people would rather not know about. It's not going to be easy.
Here lies father and mother and sister and I,
We all died within the space of one short year;
They all be buried at Wimble, except I,
And I be buried here.
Headstone in a Staffordshire churchyard.
Photo of headstone fragments by the wall of St. Peter's Church, Elmsett, Suffolk © M Nelson.
Photo of bones in an ossuary in Sedlec near Kutná Hora in the Czech Republic from the Czech Tourism website.