Does gay marriage raise divorce or species-extinction rates?

A tentative "no" to the first, says Nate Silver, after an analysis using CDC data.

Specifically:

Overall, the states which had enacted a constitutional ban on same-sex marriage as of 1/1/08 saw their divorce rates rise by 0.9 percent over the five-year interval. States which had not adopted a constitutional ban, on the other hand, experienced an 8.0 percent decline, on average, in their divorce rates. Eleven of the 24 states (46 percent) to have altered their constitutions by 1/1/08 to ban gay marriage experienced an overall decline in their divorce rates, but 13 of the 19 which hadn't did (68 percent).

There is a lot more, none of which implies that states which permit gay marriage pay a consequent divorce-rate penalty.

Regarding gay marriage and environmental issues, Eduardo Peñalver reports that the pope, as a part of his disappointment over failure to reach a climate change agreement in Copenhagen, said:

Creatures differ from one another and can be protected, or endangered, in different ways, as we know from daily experience. One such attack comes from laws or proposals which, in the name of fighting discrimination, strike at the biological basis of the difference between the sexes.

Peñalver reasons his way through the associated papal moral logic, concluding:

There seems to me to be a consistent failure here to acknowledge the existence of a point of view that largely accepts the Pope’s suspicion of liberal rights and autonomy talk, but that nonetheless supports gay marriage (and contraception) on grounds rooted in the same traditional beliefs in duty, the family and public morality on which the Pope relies. I don’t support gay marriage because of a radical conception of individual autonomy, but because I don’t think homosexuality is immoral. And, because I don’t think it is immoral, I think the law should encourage and assist gay couples, as it does for heterosexual couples, to root their sexual lives in the stability of legally sanctioned marriage.

Very different paths through altogether different thickets to very similar conclusions.