Astrophysicists predict that the end of the Earth will occur in around seven and half billion years by which time the Sun will have exhausted its core hydrogen and will be in its red giant phase. During this phase, the Sun will expand to around 250 times its current size and also a few thousand times more luminous than today. As it expands, Mercury, Venus and Earth will be engulfed however life will have long been extinct on our planet before this due to stellar evolution. 

There are many possible theories as to how humanity will become extinct. 

Climate change - increasing levels of greenhouse gases from fossil fuels, deforestation and human population growth could result in human extinction. 

Supervolcano - the volcanic winter that would follow the eruption of a supervolcano would be similar to that of a nuclear winter.

Pandemic - previous pandemics such as the Spanish flu is estimated to have killed around 5% of the world's population at that time.

Overpopulation -  the human population is predicted to grow to around 11 billion by 2100.

Nuclear/biological weapons - should World War III ever occur, the nuclear winter that could follow may lead to widespread crop failure and famine. 

AI/nanotechnology - self-replicating super intelligent machines would consume all biomass on earth.

Asteroid impact - asteroids that have collided with Earth in the past have lead to the mass extinction of several species. The Chicxulub asteroid that impacted the Earth at the end of the cretaceous period was around 6 miles in diameter and is estimated to have killed up to 75% of all plant and animal life.

Cosmic event - A gamma-ray burst or solar flare could have devastating consequences for life on Earth. 

Stellar evolution - it is predicted that in around 4 billion years, the increase in the Earth's surface temperature will lead to a runaway greenhouse effect. Eventually the temperature will be hot enough to melt the Earth's surface. 

Extraterrestrial - invasion of a species from another world. 

These are just a few of the many theories that exist.

My question is, how do you think the end of humanity will occur? Or will it occur at all? I'm interested in hearing your thoughts. 

You've made a nice summary of the commonly thought existential risks or risk factors that humanity faces. I think other points to consider how disruptive technologies are outpacing our collective wisdom. (ie. CRISPR and germline editing).

If you are really interested in this topic, I would recommend The Precipice by Toby Ord, who addresses many of these points. Sam Harris' Making Sense Podcast has touched on these topics a lot, Toby was a recent speaker as well several speakers talking about risks associated with nuclear weapons.

There is this quote from Men in Black (not really in context for this):

"A person is smart. People are dumb, panicky dangerous animals and you know it..." My pessimistic side thinks, we will be responsible for our own extinction, right now, we are off track to mitigate emissions and there have been too many close calls with nuclear weapons. I hope I am wrong and we make it a priority to mitigate existential risks, but hard to build that into a 4-year election cycle (USA).

We might not even know of the appearance of artificial intelligence in order to save our lives, but they could help save our lives.
Perhaps, as it's argued in the book The Future of Mind, there are myriad ways that our civilization might use AI to "improve living standards, enhance and prepare" itself.

This is why Musk has called for a universal basic income to remove one of the main risks of AI, economic disenfranchisement.

Thank you Germanicus for the recommendations. I'll definitely have a look at those as its one a handful of topics similar to this that I find interesting. Thank you for your insight. Hopefully we get to hear a few others too. 

You are welcome Edea, you bring up a good point @Anubus regarding AI, it's thought that the continued advances in AI and automation will lead to a "useless class" of people. "Useless" in the sense that algorithms and automation will be better at performing people's jobs than they are. This isn't expected to end humanity but if this isn't addressed (ex. mitigated through UBI), this has disastrous consequences for the individuals specifically impacted, but society is sure to feel the ripples. 

I believe the world is going to end by zombies a new super virus and people will start turning like rabies or something to that extent you will have to survive

I think we will die by a new super disease in time. Not exactly like the plague but similarly. With the overuse of antibiotics etc we will not be able to protect ourselves too much against it.

How ever it will occur, it will be very stupid. That is the only thing of which I am certain. As for the options presented, I'm rooting for extraterrestrial invasion. We'd make great pets.

End of humanity? Well, before I give you my two cents, I am an atheist. Saying this, you should now know if you want to keep reading or not. 

So, I've always been someone highly enthralled by science, moreso, math. This love for science and math helped me hone my logical thinking and helped develop my criticism and skepticism of what are senses perceive. It's also made me able to question things that seem believable at a first glance, in other words, it's helped me disconnect my beliefs from evidence, facts and empirical testing.

With all that said, I believe, for lack of a better word, in what we are able to prove and calculate. Everything else is in the realm of possibilities. (Note that when something is proven, belief plays no part in it. Whether you believe in it or not doesn't change the fact that the fact in itself is true. For example, people can believe that the Earth is flat, vaccines cause autism, etc., but, at the end of the day, they are wrong even if it's what they believe in. I chose the word believe earlier because I've been doing math for the past 10 hours and my brain is fried and I can't think of the correct word right now). 

Now let's get to the meat and potatoes: Without going into detail, what I believe to be the end of humanity is supported by evidence in which that evidence does increase the probabilities of a certain end. These probabilities are what drive me to believe in a certain end. 

First off, the end of humanity will almost certainly happen one day. At the current rate of the change of status on Earth, humanity won't survive much longer unless we change our way of living. If we do manage to survive this ordeal, then we have to worry about the sun. The sun is a star and the star will implode on itself in, from what we currently can calculate, 5 billion years because of the lack of hydrogen. When the star implodes, it will then explode, which means humanity has to get the fuck out of dodge, so to another galaxy that can support life, assuming we haven't crossed into the horizon of a black hole, from which, there is no coming back. After this, from what we know, the only other certainty of the end of humanity is when the universe has expanded so much that matter becomes too thinned out. We are made of matter, so I'll let you think of what that entails. 

Tldr: I believe the end of humanity will happen when we can't adapt to the climate change the Earth will undergo. We can try to prevent the drastic temperatures by changing our way of living. If we do, then the next end of humanity will happen when the sun explodes. If we're able to circumvent this event, the next end of humanity will occur when our universe has expanded too much. 

I do want to say that we can all die in a variety of other ways. Nuclear Armageddon, an asteroid too big for us to handle, etc. 

My last post only talked about events that are certain to happen which means that we are certain to die, unless we can plan around these events.