The position of this prophecy in the order of events, namely that it's following a fiery hailstorm and a gigantic asteroid, possibly even two of them (wormwood may be an asteroid), it doesn't take much imagination to picture the cause of this judgment against Earth.  If you've been following the wildfires out west in Oregon and beyond, you'll notice an interesting phenomenon.  For anyone who has heard of either "Atomic Winter" or "Volcanic Winter", both of which are conditions where so much dust and debris, and even smoke, has been thrown into the atmosphere that it blocks out the sun causing either most or all of the light and heat being sent to Earth to be reflected back into space.

As such, this will cause an incredible cold that will impact the entire planet.  Those who are used to having to survive super cold winters won't have as much of a problem getting through this.  But if the world has indeed been turned on its axis and the crust shifted considerably, such as is believed to happen during in the 6th seal judgment, even that may not protect some people. However, even if the crust does not shift, and all remains the same, there will still be many who will freeze to death because of the extreme cold that will occur at this time.  Even the tropics will be affected.

And it's very likely that this and the prior three judgments will all be concurrent with each other, meaning that first the hail and fire mixed with blood will fall, and while people are dealing with that the mountain cast into the sea (possible mega asteroid) will fall and destroy a third of the sea, and while they're dealing with the consequences of that, wormwood will fall and poison 1/3rd of the drinkable water.  And then to add insult to injury, this powerful, cold, winter like plague of darkness (appropriate given the time period) will cover the entire Earth plunging the temperatures into the negative digits as far south as the equator.