This phase takes place right after a season change.
In Autumn, each Industry tile also causes the humidity of its own space and all surrounding spaces to drop by 1.
Aridification does not lower the humidity of a space below 0 and does not stack; only the largest humidity drop per space actually takes place.
Furthermore, at the start of Autumn global warming is increased. Each populated tile causes a number of spaces to gain a Chaos counter; every City tile generates 2 counters, every Industry tile 5 counters, every other populated tile 1 counter, and every Rubble tile also generates 1 counter. If a space would gain a Chaos counter but already has one, a random tile other tile will gain the counter instead. Forest tiles cannot gain Chaos counters directly; these Chaos counters are discarded. However Forest tiles can gain Chaos counters indirectly when a Chaos counter would be put on a space that already has Chaos. Once every space has a Chaos counter, no more Choas counters are generated.
Then, spaces gain or lose weather effects depending on Humidity and Chaos. Snow occurs in Winter if a space has 1 or more Humidity and in other seasons when a space has 4 Humidity. Frostbite occurs in Winter on all Grass, Dirt, Desert, Rubble, Soil and Crops tiles if at least 20% of the map is covered by Chaos. Firestorm occurs in Summer at random on 4% of the map for every 40% of the map that is covered by Chaos, prefering Grass, Forest, Soil, Crops and Trenches tiles and avoiding other tiles if possible. Bonedrought occurs on Desert tiles if at least 60% of the map is covered by Chaos. Bonedrought also occurs on City, Town, Farm, Barracks, Industry, Airfield and Rubble tiles if at least 80% of the map is covered by Chaos. Once 100% of the map is covered by Chaos, Death is placed at random on a number of populated tiles equal to 1% of the map. Death stays on those spaces until the end of the game.
After these weather changes, natural tiles can grow or transform. Only one effect can take place in each space. In spaces without humidity, Grass tiles become Dirt and Crops tiles become Soil; if at least 40% of the map is covered by Chaos, Dirt and Soil tiles become Desert. Soil tiles in spaces with humidity and without snow transform into Crops tiles. In Spring, Grass tiles in spaces with humidity and without snow have a 50% chance to transform into Forest tiles with one tree; Forest tiles in such spaces have a 50% chance to gain a tree.