The Great Thaw

500 years have now passed since the end of the Mid-Ultimocene, since the massive coal-seam fire was inadvertently set ablaze underneath Serinarcta. It is still actively burning more than a hundred million years worth of accumulated carbon and now spread over most of the landmass sometimes above, but primarily below the ground. The enormous fire smolders underground constantly, occasional forming shorter-lived surface fires that spread over the land and extend the fire's reach into new underground seams. So protected from the wind and the rain, such hidden subterranean fires will continue to burn as long as these enormous reserves of fuel still exist. Subterranean heat over such a wide area began melting the northern glaciers within a century, forming a layer of liquid water beneath the glaciers and causing them to slide and break apart, and now the permanent ice is gone over much of the northern continent. Dark soil now absorbs more solar heat instead of white ice reflecting it, and the heat is retained in the atmosphere newly filled with large quantities of carbon dioxide from the continuous blaze. Additionally, pockets of methane produced by bacteria and once locked beneath sea ice are now released in huge amounts; though its presence in the atmosphere is short-lived, it functions briefly as an even stronger greenhouse gas, hastening an already rapid change of climate.

Vegetation quickly reclaims melted land, and for the hardiest land animals that made it this far, the hard times are now behind them. But this reversal of climactic course brings with it its own destruction, as melting ice and extreme temperature differences between poles and equator begins to cause rapid sea level rise and the formation of powerful, turbulent currents. The ocean age ends ironically with the increase in depth of the oceans, causing the death of the widespread underwater meadows that relied on shallow sunlit water to grow. Almost all of the sea's specialized herbivores as well as the carnivores that hunt them are doomed. As the range the vegetation can grow recedes to rapidly expanding coastlines there is now much less food available, and the water along the new coasts is becoming far warmer than they were adapted to, causing die-offs and subsequently severe algae blooms, including toxic red tides. Water quality is worsened by acid rain, acidifying the oceans severely. Along coasts worldwide, marine creatures continue to wash up dead and dying. The oceans will still get worse before the world recovers again and adjusts to its new normal, with more than 95% of their endemic life ultimately becoming extinct in the worst mass-extinction event since the Thermocene-Pangeacene boundary.

On Serinaustra, a continent locked in ice for millions of years, the death of the sea feeds new life on the land. Snowscroungers marooned on the ice for millions of years and foxtrotters that arrived here just five centuries ago now feast on the dying sea animals that wash up on their shores. Glacier ravens are joined in the buffet by their larger relatives, imperial sea ravens recently flown over from the Meridian islands. So much meat is now available the animals don't need to fight over resources either amongst their own kinds or with each other, and even solitary snowscroungers begin to associate in groups. All of the carnivores now bear large, healthy litters, with most of their young surviving to adulthood, and for them life is good.

Their once icy world is now unrecognizable, for there is now thawed land and vegetation. Hardy low-growing sunflowers, clovers and puffgrass have crossed the widened sea on the wind from the north, and taken root on a melted coastal plain. They have been followed already by the first wayward pairs and groups of small grazing archangels, which were the melted continents' first grazers. Now however more are arriving - duck-billed sealumps, fleeing the collapsing oceanic ecosystem, now arrive in large numbers and graze upon the land in a place where no predators yet threaten them. With still-functional legs, they alone are saved the fate of their other aquatic relatives that lost the means to walk above the waves to find food, and which will very soon be extinct.

In Serinarcta, the glaciers are now gone over nearly all of the northern landmass. Vegetation has returned, dominated by puffgrasses, and wide open plains now cover the continent, supporting herds of several million nimicorn thorngrazers and their sawjaw predators. Nearly all surviving animals here benefit from the warming, yet for a few which depended upon sea ice, and which lacked the competitive edge to survive anywhere beyond their refuge, this becomes their nail in the coffin. Icefisher gravediggers, isolated and widely dispersed, are unable to survive alongside their much larger savage relatives. Only one species of this once widespread genus now carries the torch to go on in the new world that they face.

The loss of all that ice now brings forth its own novel dangers even to less specialized species. A new self-perpetuating cycle has been initiated which will continue to warm Serina for millions of years to come, even after the coal fire dies out. A jackal carnackle in fast pursuit of three steppe snoots, evolved from the snow snoot, is stopped in its tracks by a boiling torrent of exploding water rising from the earth. A deafening blast and a cracking deep in the crust, then the whistling of scorching hot steam. The horrified hunter stops inches short of being burned alive by the birth of a geyser, and the snoots make their safe escape. A skewer is startled into flight from its resting place in the tall grass, while a lumpus, unable to run, can only look on in what may be horror or just passive indifference - it's rather hard to tell.  The sudden relief on the moon's crust from the crushing pressure of all that heavy ice pack now initiates Serina's final burst of volcanic activity, and triggers eruptions all across the northern hemisphere that add even more greenhouse gas to the atmosphere. 

Millions of years of built-up ice over the land exerted an extreme force upon Serina's crust, deforming it and forcing what little active volcanism still existed near the surface into concentrated subsurface pockets. With the pressure now relieved, magma rises to the surface. The first sign of changes to come is the formation of geysers where explosive boiling-hot water erupts from the newly-thawed earth, throwing rocks at high speed into the air and turning the plains into a deadly minefield. Next to come is the magma itself, as new volcanoes come to life after tens of millions of years of dormancy. Massive cinder cones erupt and form in just days, towering up to one hundred and fifty feet into the air. The next few hundred thousand years will be turbulent, with volcanism producing clouds of debris in the atmosphere that will reduce the amount of solar warmth reaching the ground on the very short timescale, but ultimately releasing huge quantities of carbon dioxide, which will result in even more rapid global warming than the massive burning coal seam alone can produce.

This guest illustration was done by Troll Man 

The hothouse age will soon begin. Though this shift of climate is impermanent, it will be much longer-lasting than the ocean age, for even though volcanism is still weakening below ground, the Serinarctan subsurface fire and ongoing northern volcanic eruptions induced by the disappearance of glaciation will continue filling the atmosphere with enough carbon dioxide to delay the onset of the next ice age for twenty-five million years.