Washington Post: There are things about summer — long days, shaved ice, fresh-off-the-tree-peaches — that we love. And then there are those things we simply tolerate because, well, the pessimist in us says that life can’t possibly be that perfect, so we must suffer, just a bit. Well, it appears we could be suffering a bit more in coming days. Polar bears might be endangered because global warming is melting their homes on arctic ice shelves, but one species is thriving: poison ivy. A …