Complete Ice Age is an achievement that can only be won with the Scenarios DLC.
How to get this achievement?
I found the achievement via ProjectSix and worked perfectly on Pc
Use the Neurax Worm virus. You can get this achievement playing on casual difficulty.
Metabolic Jump (feel free to use Metabolic Hijack if playing on casual) Genetic Mimic Native Biome Extremophile Trans-Stasis.
1. Start in India
2. Evolve ALL the transmissions, but evolve these five Transmissions and this Ability first:
Genetic Swap Corpse Feeder 1 and 2 Mutative Regeneration 1 and 2 Trojan Planes 1
3. From here on out, send the planes to any island (you'll see an orange plane icon pop up from Trojan Planes, click it then select the country to infect) if they haven't been infected yet. Start in Greenland, then Iceland, then Caribbean. You choose the islands after that. Just hit Y for the world screen and see which countries aren't infected. If all the islands are infected, then go after healthy countries next. If every country is infected, go after the biggest research contributor.
4. Evolve Cold Resistance 1 & 2, then Drug Resistance 1 & 2
5. Evolve these Symptoms if they haven't mutated yet (the first two are basically always mutated by this time): Neural Breach Cerebral Tendrils Frontal Mesh Immaturity Mania Obsession Devotion Adoration Transcendence
6. Rest of the DNA can go to whatever you choose. I prefer going after the evolutions that increase infectivity, though. If for some reason your cure % is getting high, you can use Genetic ReShuffle 1 & 2 if necessary.For more information, please see Ice Age.