Rainbow Mars

From back cover Tor paperback May 2000:

Hanville Svetz was born into a future Earth that matches the sorriest predictions of Greenpeace. With most of Earth's original species extinct, Svetz travels back and forth in time retrieving them. Svetz learns that Mars was inhabited, and how the sapient Martian species were wiped out. He foresees that Earth could soon fall victim to the same fate.