XKCD's hilarious 'What if?' series answers another farfetched question as only they can. The question: If every person on Earth aimed a laser pointer at the Moon at the same time, would it change colour? The simple answer: not if it's a regular laser. But if the lasers were stronger... we might just die.
The question is how strong can we get? XKCD considers the power of green lasers, Nightsuns, IMAX projectors, Luxor Las Vegas beams of light, megawatt lasers and megawatt lasers on every square meter of Asia (that would use up Earth's oil reserve in two minutes to power it all) The best explanation, though, is if we somehow gave everyone on Earth the most powerful laser on Earth (the confinement beam at the National Ignition Facility):
Let's imagine we somehow found a way to power and fire it continuously, gave one to everyone, and pointed them all at the Moon. Unfortunately, the laser energy flow would turn the atmosphere to plasma, instantly igniting the Earth's surface and killing us all.
Read the whole hilarious breakdown at XKCD. [XKCD]