Icehouse Apterra

The Sea

It has been 100,000 years since the Late Muricene concluded. The Ice Age extinction event has begun in earnest, with no corner of Apterra left untouched. Before, climate change occurred gradually, but a chain reaction was set off sometime in the last 50,000 years. Cold spells at the equator led to massive swathes of algae dying, after which a new mat would regrow, only to be killed again by the next freeze. With each die-off and regrowth, more carbon was removed from the air, causing additional cooling, killing still more algae and sequestering greater amounts of carbon. This hyperaccellerated biological pump depleted atmospheric CO2 at rates never seen on Earth. At the height of the feedback loop, carbon dioxide concentrations dropped by over a hundred parts per million in just a few centuries. Algal growth stalled due to the lack of available carbon, so the sequestration process subsided, but not before carbon dioxide levels reached their lowest point at 140 parts per million, making the global ecosystem grind to a halt.

The Plants

When the Great Decarbonisation struck, most land plants immediately died, suffocating from the lack of this vital component of photosynthesis. Pseudoforests and grasslands were wiped out, and animals followed soon after, dying from a combination of starvation and oxygen deprivation. After a few centuries, the influx of rotting organic matter brought CO2  back to a liveable 160 ppm, and it will likely hover around that level for the remainder of the Ice Age. By that point, though, much of the damage had already been done. About 10% of all plant species went extinct in a span of about three hundred years following the initial collapse.

No major plant families were entirely lost during this first wave of extinctions, but some groups were hit harder than others. The tropics have ceased to exist, so all species that could not survive at least the occasional freeze have been destroyed. Even among those that could handle the new climate, it was common to see whole populations wiped out by the Decarbonisation. Luckily, caches of years-old seeds remained alive underground, germinating upon the return of survivable conditions and preventing thousands more extinctions. 

In Apterra's new atmosphere, slow growth rates are the best way for a plant to survive. For example, wax-palms have almost fully replaced basket-bushes in the taiga, as the latter no longer has the advantage of fast-growing blades. One of the hardest-hit groups was the skystalks; their nectar production required large supplies of atmospheric carbon, and over half of all Late Muricene species no longer exist. Sweetstalks were an exception, with their conservative use of nectar giving them an advantage over the rest of their subfamily, and they are among the only plant genera currently expanding their range. 

The Animals

During the floral collapse that kicked off the Ice Age, oxygen levels also declined due to the lack of photosynthesizers. Many animals could not withstand this, and unlike the plants, most could not simply enter dormancy and wait for oxygen to return. Consequently, animals (especially large-bodied ones) saw great losses, with more than a quarter of genera going extinct. The survivors were mostly those that, for one reason or another, were resilient to an anoxic environment. Alpine species like mountain kiwis and rattaloxen, already adapted to breathe thin air, expanded into the lowlands. Burrowers like Subterrapteryx, accustomed to the stale air of their dens, were similarly prepared for this event. Oceanic birds like seawis, capable of holding their breath for up to 15 minutes, had little trouble when O2 decreased, simply reducing the length of their dives in response.

Overall, birds were more likely to survive than mammals. With their one-way lungs and an extensive system of air sacs, most managed to avoid suffocation. Rats, on the other hand, lost more than half their diversity; besides the rattalox, all that weighed over a few dozen kilograms died out. This one surviving megafaunal species is now responsible for the upkeep of all of Apterra's rat-grasslands, which are now a nearly even mixture of prairie rat-grasses and rat-grains. With grainzelles, shuckertooths, and millertooths dead, the loss of the rattaloxen would at this point result in the total collapse of rat-grassland biomes everywhere. Thankfully, the herds are stronger than ever, and with them, rat-grasslands have expanded greatly. After the sharp decline of sodstalks and amber skystalks, woodlouse-grasslands failed to recover in most areas, being quickly replaced by their Magnigranaceous counterparts. Central Ailuropia, now almost fully cut off by glaciers from the rest of the world, is the final holdout of the woodlouse-grassland and its endemic animals. What was once Gecko Isles also possesses a few tracts of skystalk prairie, but large terror kiwis, skeeter-snappers, kiwizelles, and other unique woodlouse-grassland fauna are not present there, being restricted solely to the Ailuropian lowlands. Raspbirds, meanwhile, find great success in the expanding taiga, a biome that now covers more than 30% of Apterra's land. 

The Land

A further drop in sea levels has exposed the continental shelf around the Gecko Isles, eradicating the seabasket forests and creating a single landmass called Aglirium. This remains distinct from nearby Abeli's shore due to the latter's steep slopes and the continued erosion of sediment from its northern estuary. While the Isles' old tropical climate is gone, cold-tolerant lizards flourish here like never before, with huge monitor geckos prowling the pseudoforests and spine-backed Sentisaurus expanding across the plains. Thalassaurs have begun to spread throughout the Medithalassic, breeding on the Abelian and Loxodian coasts and even venturing as far as the Ailox on their migrations. 

Land has also risen above the waves in the west, creating a permanent land bridge to Choeropica. Abeli, Sub-Abeli, and Loxodia now have no meaningful separations, with thin connections growing into broad, low-lying tracts of rat-grassland. Overall, Apterra's land has never been more physically united; hypothetically, an individual could freely walk across unimaginably long distances, traversing entire continents within a single lifetime. In reality, habitat fragmentation prevents such journeys; habitable land is mostly found around the margins of continents, and vast stretches of a single productive biome are mostly a thing of the past. Even some shorter crossings, like the once-brief trip from northern to southern Abeli, are blocked by walls of ice. With so much water trapped in solid form, rainfall is at an all-time low worldwide, and cold deserts dominate many inland regions. Nearby, what remains of the ten-year desert is Apterra's only remaining hot climate, though colder arid conditions now occupy much of its former area.

The alpine ice caps of the Muricene have expanded into continent-spanning glaciers. Northern Loxodia is mostly covered by the East Ailox ice sheet, while the western continent has two: the Northern and Southern Ailurentide ice sheets. Abeli's two mountain ranges, as well as much of the nearby lowlands, are connected by the Gillywog Glacier Chain. Smaller ice sheets also exist across Panapterra, the Northern Isles, and Unciolis; only Choeropica and Aglirium are ice-free. Unciolan lakes have begun to freeze over, then solid, stifling any complex life within. This will soon be the fate of both lake Ailox and the lake where great red stoutlings breed, forcing their endemic life to either flee or die. Sea ice, on the other hand, is still rare, as Apterra has no land at either of its poles, and fast-moving currents prevent large floes from amassing.