The air was too dirty to support them. We solved that problem with better technology, not by returning to a 17th century lifestyle. Modern cities are full of beautiful, flourishing trees. That is the model for solving global warming, too, if it can be solved.

That's part of the rationale for carbon credits. (Again, I'm not
claiming the implementation works, just what the theory is, AFAIK).
Someone flies a relatively clean jet (or fires up a relatively clean
refinery), and pays money to those who have relatively dirty ones. They
the money and use it to clean the dirty ones up.

The idea is that it's less expensive to improve the dirty ones than to
get the same reduction in the ones that are already clean.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.