The tragedy of the commons goes like this: if you have a common use pasture that all farmers can use, the logical thing to do is put more cows on that pasture because the economic benefits are exclusively the farmer’s, while the costs are shared by the entire community. It is therefore more profitable to try to over exploit the pasture, if all farmers do this, and logically they should, then the whole pasture fails from over exploitation.
In reality, this doesn’t happen in small communities. The reason is simple- if everyone knows everyone else, there ARE greater costs to over exploiting and using more than your fair share- social penalties. If you ruin the whole thing for everyone else, you damage your own social standing, which in a known community can harm you more than you’d gain.
In large communities this doesn’t work however, as anonymity undermines the social repercussions effectiveness.
At this point the argument is made that the answer is private ownership is the answer- after all, then the only person you harm by over exploiting is yourself, right?
It’s actually no different. Mentally divide the common pasture up into “land that has already been fed off” and “land that has not been fed off” adding an extra cow won’t increase the amount of pasture available to your cows either. Your cows suffer as much from under feeding as everyone else’s. Does this benefit you? You can’t guarantee that just because you have more cows, that they’ll get more of the available food than everyone else’s cows.
With many resources, private land ownership does not mean you’ve stopped this, as environments do not stop at land boundaries. If you cause salinity and erosion on your land from over exploitation, that could still have impacts on nearby land.
When you get to aquatic systems this becomes even more profound.
Just look at the gulf oil spill or fukushima’s radiation spread. You can’t just divide something up into pieces and expect everything to be fine any more than cutting a house or all your furniture in half makes them reasonable to split along arbitrary lines.
Privatisation of natural resources does not mean they will be better managed or preserved, it just makes the over exploitation devoid of any personal responsibility for the degradation and undermines the efforts of other, responsible management schemes through fragmentation or spreading effects, particularly through shared resources such as water (ground, river, lake or oceanic) or air, wildlife or seed distribution.