they make a hole in it and jump over the cliff:
One of the best ways to reasonably enjoy your pet and reduce your overall Carbon Footprint is to determine in advance how long your pet should live. As a family, set a date when your pet will be euthanized. One great way to teach children the value of pet euthanasia is to turn the occasion into a family celebration.
Until governments wake up and start passing "one child per-family" laws, the best way you can help reduce the collective Carbon Footprint is through voluntary sterilization.
Read it. It's... disgusting, for lack of a better description right now.
Update: they say it's a spoof. Problem is, the 'get rid of too-many people' stuff is fairly standard greenie dogma; makes it hard to tell