It was a Thursday afternoon just before lunch when I came to the terrifying affirmation that mankind is doomed and it's all our fault.
My epiphany was less a realisation than reluctant acceptance. For all our iPad techno-whizz and hadron-colliding Mars rovers, our species simply isn't equipped with the capacity to combat the most immediate threat to its existence.
This ultimate apocalyptic gravitas struck at a peculiar moment. I wasn't fighting alien attackers nor intercepting a fast-approaching comet before it blew through the atmosphere and decimated existence. I wasn't crawling with the plague or even contemplating the progress of Iran's nuclear programme.
I was standing at the cash register of a budget supermarket with a $2.50 bag of carrots and a stick of peppermint-flavoured gum, when the cheery young man behind the counter double-bagged my groceries.
"Ahh, actually I don't need bags."
"Are you sure?" he said, surprised, as though along with my change I'd politely asked him to punch me a few times in the teeth. "They don't cost anything."
The last time I checked, plastic bags weren't entirely swell for old Mother Earth. Even the most planet-hating climate change denier would have to concede that double-bagging a single bag of bagged carrots is a little unnecessary. It's bad business, although at many stores in the United States it seems to be the norm.
It's been a rough summer here. A filthy, sweaty-shirt-clinging-to-your-back summer in which last month alone more than 3000 national heat records were broken. More than half the nation's counties were labelled natural disaster zones by the Department of Agriculture.
Last week about 40,000 shovelnose sturgeon were found dead in the state of Iowa after their waterways became too warm for them to survive.
Less than reassuringly, veteran climate change scientist James Hansen, who first warned the Senate of global warming in 1988, has fresh research which concludes that this year's heatwave is certainly a result of man-made influences. Hansen says it's our fault it's hot, and he was only mistaken once in his address to the Senate, 24 years ago.
"I was too optimistic." With those words ringing in my ears, I considered returning home with my $2.50 of triple-bagged carrots, turning on the air-conditioning and ignoring the heat. Grocery prices are being driven up by the heatwave so my carrots won't stay that price for long.
Oh, and last week a power plant in Illinois had to shut down a generator after its water intake was blocked by a mass of heat-killed fish. So perhaps I can't rely on the AC either.
The United States isn't the only country to contribute to greenhouse gas emissions. Indeed, all countries do, and it's worth pointing out that right next to the double-bagging supermarket is a seemingly efficient aluminium recycling centre.
But as the country that professes to lead the free world, stronger American leadership in actively reducing greenhouse emissions seems desperately lacking.
Al Gore thought so. It cost him his office.
Barack Obama thought so, too. At least he did before the last election. Then, given four years, not much really changed. The only real difference in his Earth-saving policy this time around is that he's making fewer pledges.
Mitt Romney, on the other hand, supports a greater use of coal energy and says mankind is only "somewhat" responsible for climate change.
The extended forecast then, as the election season heats up, is for plenty of hot air and little immediate change. What's the point in trying to save the world if it costs you an election?