"What Is The Biggest Possible Threat To Humanity?"!

That's Quite A Sidebar Title -
 - I think you'll admit.  There is, lest you be unaware, quite a list of things that might cause Hom. Sap. to shuffle off this mortal coil en masse.  As a mild diversion, and because I can't remember the name of the splendid Dutch website that listed all the myriad ways of deadly demise, I shall explicate some of them.
     1)  Major impactor.  Either a meteor, stray asteroid or comet, anything beyond a critical mass will cause a mass extinction event for all life on planet Earth.  It's happened before, it will happen again, and the only question is when?  Art?

Way back when

     If there's sufficient warning, a robotic probe carrying a multi-gigaton warhead might be able to divert the killer rock, but - don't bet on it.
     2)  Global Thermonuclear War.  Not as dangerous as it used to be, when NATO, the Warsaw Pact and Communist China were all pointing lots of these weapons at each other.  The end result today would be several orders of magnitude less than, say, in 1980, but it would immediately put civilisation back to 1850.  Not good.

Sounds like a plot-line, however ...

     3)  A.I. and sentient robots.  This one is theoretical at present, yet coming closer every year, to the point that scientific bods are e'en now pontificating about whether Marvin the Paranoid Android should be given psychiatric counselling or a reboot.  An A.I. sufficiently developed would potentially see all you us mobile meatbags as threats to it's own existence, and thus Skynet.  Or, sentient robots would see us as potential competitors for resources; potential competitors with weaknesses like pain, hunger, fear, oxygen, water, food and Banana Flavoured Twinkies, who would thus be easy to sweep out of the way.  

The thin end of the wedge, believe me.   THE THIN END OF THE WEDGE!

     4) Alien invaders.  Rather more in the realm of enormously speculative, because any such invasion would involve slower-than-light travel, and we'd all probably be long dead by the time our sinister slinking extra-terrestrial overlords arrived.
     Still, we only have to be wrong once ...

Of course, some are more invader-y than others.

    5)  Ecological collapse.  You know, the icecaps melt, sea levels rise, the ozone layer disappears, the bees all die, pollution kills off plankton.  Makes for a fascinating novel, much less entertaining to actually live through.
     "But - what is this threat you teased us with, Conrad?" I hear you question.
     Ah yes.  Art?

Intriguing sideline, hmmm?

     The thing is, after taking this photograph and getting on with work, the Beeb's website moved the article.  Could I find it afterwards?
     Well, of course I could, because I am Conrad: nothing if not dogged and persistent, though it took 10 minutes to locate it.  What did I find at the webpage?

"The flu that killed 50 million people"

     An article about one disaster I omitted - a global pandemic of flu.  It is 100 years since the outbreak of Spanish Flu whilst the First Unpleasantness was still raging, and the article begs the question as to whether a similar outbreak might happen again.
     What?
     This is the source of that title?  "We might get flu".  Well - what a disappointment!  I expected an atom-bombed Moon fragmenting and bombarding the Earth, or -

But Then Again -
There is an effective short story by Stephen King called "Night Surf", where the story is a narrative as told by one of the survivors of a "Superflu", codenamed A6, that came out of South-East Asia and destroyed the world.  Only those who previously suffered and survived another flu strain, A2, are immune - or so they think.

Based on the colour palette alone, you know this isn't going to be all lovely cuddly bunnies.

Well, haven't we been all grim and foreboding!  The death of practically everyone and everything.  Of course, if a global pandemic finished off Russell Brand and Alan Carr it would almost be worth it.  Almost, but not quite.  Not unless you can guarantee that it'll also finish off that flat-chested stripper (?) ass-waggler (?) surely not a musician (!)  Miley Cyrus as well.

"Influenza"
Whilst we're on the subject, this is the full name of what we normally abbreviate to "Flu", apart from me, because I speak proper.  It comes from the Italian for "Influence", because folks in times long past thought that perceived relationships between fusion furnaces thousands of light years apart - a.k.a. "Astrology" - caused the illness.

I predict - a riot!

     When people eventually sobered up, or stopped eating wheat contaminated with ergot, they realised astrology was as scientific as the study of goat's entrails when it comes to causation, so it became "Influenza di freddo" or "Influence of the cold", which is howlingly ironic.  Why so?  Because the only regions where it is endemic all year round are the hot ones around the equator.
Okay, enough of disease, depression and misery.  Time to lighten things with a treatise on LITHIUM WAFER BATTERY DESIGN!
     Why aren't you laughing?