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#1) Amazing Spider-Man #636-- Breaking the Web of Life.

Michael Lark and Stefano Gaudiano, Marvel Comics (2010)
The "Grim Hunt" continues as the Kravinoffs intensify their extermination of spiders. Unfortunately, according to Madame Web, these spiders play an important role in a delicate ecosystem (or something). By hunting them, the Kravinoffs have accidentally disturbed the balance of nature, forcing a bunch of angry rats, gorillas, birds, lions, and others to respond by killing more humans.
#2) Irredeemable #15 -- Accidental Earthquakes
It's bad enough that the Plutonian destroyed Singapore, along with several other major cities in the world. Now in his fight against him, Cary has impetuously driven the Plutonian into a fault line, causing a 9.8 quake that's spread as far as 221 miles away to Phoenix. Incidentally, in the last issue the Paradigm (former eminent superhero team in this universe) specifically picked the Grand Canyon as the location of the fight to avoid causing damage and externalities such as this. Whoops.
#3) X-Force #28 -- Golden Gate Bridge
When last we checked in on "Second Coming," the Golden Gate Bridge had been surrounded by a mysterious dome, engulfing the new mutant haven, Utopia, along with a good chunk of San Francisco. We later discovered that the dome was actually a portal, sending "mutant-slaying Nimrod sentinels" back from the future to, well, slaughter mutants. Now it seems the battle is over and the Nimrods are all but destroyed. Except...yeah.
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Feel free to send us your favorite externalities of the week. We'll throw them up on next week's post and credit your name.