What are they? Chris Chan answers that in the latest Gilbert Magazine.
As you probably guessed, the portents of doom are today's media outlets, designed to upset you and let you know how environmentally irresponsible you probably are. Which links in nicely to the News with Views article about the secret (how secret could it be if we found out about it?) meeting between the US's richest people, gathering to pray at the altar of over-population, birth control and environmentalism where it concerns having fewer people around to breathe the rest of our oxygen.
This all ties back in nicely to Chesterton's "Social Reform Versus Birth Control" article in the early pages of the issue.
It's probably a coincidence, or do you think the editors actually planned all those neat connections? Huh, I just don't know. ;-)