I had an insane idea for an expansion pack: Anno 2070 - The Troposphere
 This is the staggering result!
The concept is that we add a third layer of map, called the Sky. You zoom out to it in two magnifications just like you can zoom in toward the undersea level. You see the blurred image of the ground and your ground islands underneath, over heavy layers of cloud.
The story: some scientist or inventor experiments with gases lighter than air and by accident raises portions of land (say, those that have some mineral under them) to the sky, and these stay afloat indefinitely. He now wants help from Ark Captains to explore the land above and carry out tests etc. And of course the Eden Initiative and GT are eager to exploit the possibilities.
Skyland is just like your land islands, complete with links to the land, a new mineral type or two, and new buildings and vehicles. Transport ships in the air are Zeppelins and airships, carrying goods from land to skyland and in between sky-islands. The ecosystem would be different in that land islands affect airborne islands and vice versa. The rest I still have to figure out...
Okay I expanded a bit, here it is!
After the human race's millenia-long destruction of the ecosystem, a single person managed to up the scale even higher. Literally.
Dr. Derek, a former S.A.A.T scientist who has been relieved of his position for reckless experimentation, has engineered a massive and catastrophic change to the planet. Deposits of Thorium all over the world have drastically expanded and somehow reversed their gravimetric properties, tearing vast chunks of earth the size of a smaller tectonic plate out of the ground and lifting whole landmasses in the air, as high as 4-5 kilometers and some are still rising!
Most of the "new continents" as they are now called have raised the ground from under the Ocean-water and settlements now spread so thin over many small islands resulted in almost non-existant casualties, yet the Eden Initiative has called a planet-wide alert to caution the population to not approach any of the concerned sites and Global Trust is actively monitoring the global emergency situation.
A previously non-existant type of metal has also been revealed to form on any remaining supplies of Thorium, when asked Dr. Devi of Scientific Academy for Advanced Technologies said "The chemical we call Derium is highly dangerous and radioactive, we advise against handling it, if that is, you know what's good for you!", and is now collected by S.A.A.T and The Eden Initiative Arks. Dr. Derek has not been found since the incident, but with his whole lab and equipment arsenal missing, he's suspected to have fled to Troposphere-level ground to escape Earth authorities.
Now, 2 months later, the islands in the Sky seem to have settled and the Troposhere's harsh windy world needs to be explored, changes in wildlife and atmosphere documented, and Dr. Derek found! Welcome toAnno 2070 - The Troposhere!
Raw Gas: Extracted from the newly formed islands by the Extraction Plant, raw gas can be turned into functional form in the Bottling Factory. Three common gases may be produced from Raw Gas:
- Helium (white gas) which is used to power airships,
- Hydrogen (blue gas) which is used in conjuction with
- Thorium (mined from abundant Derium deposits) to create Shuttle Fuel
- and Nitrogen (yellow gas) which is used with Copper and Steel to create Cryo
New buildings are buildable by unlocking standard Tech construction. They will be found in a new tab next to Underwater buildings. Extraction Plant, it fills your stocks with Raw Gas. The Bottling Factory processes Raw Gas to turn it into various Gases. The Atmosphere Base is a new research building, offering new formulas and discoveries. The Airstation is the airborne equivalent of harbors on the Seas, it assembles new vehicles, which in turn power your explorations in the air. But exploration is no longer bound to the Troposphere using the new Tech Monument! The Space Center is now constructable on any new continent land, allowing you launch expeditions into Space!
The science of Dr. Derek has turned out to be scattered all over the lands of new continents, and using clues from S.A.A.T scientists new vehicles are now buildable for air-service. Airship manufacture requires Helium stockpiles as well as Building modules and Tools combined with Carbon. The standard Airship is equipped with 4 slots of storage and is most commonly used for transport, the advanced Zeppelin is a state-of-the-art airborne barge with 2 equipment slots and plenty of storage, and the high-tech Aerospace Glider allows for both ground-and airborne combat. Rumours are floating of sights of a gigantic airborne vessel which some said resembled a flying trimeran...