- Pyrotechniques increases Polar Melting, which causes 100 pollution per minute each
- Tire Prefire increases Tire Fire, which causes 500 pollution per minute each
- Toxicology increases Dumping, which causes 1000 pollution per minute each (starting at 2500)
- Potent Fuels increases Brownhouse Gases, which causes 2000 pollution per minute each (starting at 10,000)
Therefore, one suggested upgrade order is the following:
- If Toxicology costs less than half as much as Potent Fuels, upgrade Toxicology.
- If Tire Prefire costs less than half as much as Toxicology, upgrade Tire Prefire.
- If Pyrotechniques costs less than one-fifth as much as Tire Prefire, upgrade Pyrotechniques.
- Otherwise, upgrade Potent Fuels.
Global Warming Event was a Double Event, running at the same time as the Black Friday Event.
- Running from November 26 – December 22, 2015 (Taking Down Santa Event)
- 10% Gold/XP/Wood/Stone and double cards for the duration
- Together with Black Hole Friday Event
Global Warming Event next ran from March 31, 2017, by itself. Bonuses of +15% XP and +25% Gold continued from the previous event.
A free Pack can be claimed at 1 Billion accumulated pollution.