I don't like the Asteroid.
Better with a Comet, 75% CO2,
So something like this, My interpertation, not Cannon,
Condottiero, would control that
1492
late in 1492, After Columbus is long gone from Spain. Comes in high over England, then crosses Egypt, enters lower astrosphere just south of equator, Breaking up, peppers Antarctica with hundreds of Fragments, triggers massive earthquakes & Ice Slides. this triggers lots of small volcanoes, Circumpolar air Currents trap the ash so it falls across the ice cap, the Currents also help trap the CO2 from the Sublimating fragments of the Comet.
1500
the volcanoes are subsiding, and the last of the Comet, has sublimated away, Most of the ice cap has a several inch coating of black ash.
there have also been several massive summer melt lakes formed, freezing over in the winter, and growing each summer, eventually several of these reach the shore, there the water drains out into the oceans,
Cuba settled
1525
the water level has risen about six inches, this puts a massive strain on the edges of the ice shelves, and calving increases, as these bergs drift from shore, they encounter more sunlight, and the black coating, causes rapid melting. a small feedback loop has been set up.
Elsewhere the coating wasn't thick enuff to cause massive melt lakes, but it is enuff to start warming the ice, instead of a 2 mile thick chuck of ice at 40o C, you now have a chunk at 39o C
[[Actually it take thousands of years, climatologists tell us that the heat from the start of this interglacial is just now getting to the bottom of the Antarctic cap.][But whe will ignore this inconvenient little fact]]
Mexico Conquered.
1550
There is an extremely massive lake forming behind the Ross Shelf slowly melting its way thru. late that Summer a very large Berg Calves, and as it drifts away, the pressure from the lake, causes the remainder of the Shelf to crumble. A channel opens up, several Million cubic Kms of water flood out. Within months, high tides are inundating Buildings from Venice and Amsterdam, to the Basements along the shores of all the worlds port cities.
The rising water has started to effect Greenland as the water lefts the edges of the cap increasing the rate of calving. Spanish sailors tell of icebergs following them across the ocean from England south to Spain.
The rising water has flooded low shorelines along the Gulf, increasing the area of warming, the increased water vapor adds to the Green house effect. It also adds to the Rainfall, In Panama a major yellow fever outbreak kills 80% of the population of the Colony, and leads to its abandonment. 2 years later an outbreak will lead to the abandonment of the Florida Colonies.
1575
The lifting of the ice over areas of Antarctica, has lead to a second round of volcanoes, The water has risen close to 4 feet, this has had the effect of removing most of the sea ice around the Cap. What are left is the edges of the great glaciers, some a thousand feet high, setting on the sea bed miles out from shore. But even here there is an affect, as the ice is now at 14 degrees C.
There is a massive building of new seawalls and Dykes around the world.
1592
it has been 100 years, and a tipping point is reached, Several of the Glaciers start melting, Not just forming melt lakes on their top but melting all over their top and sides, like a giant ice cube, millions of Kms of water flow off them during the summer, the water is enuff to raise the level another 2 feet. In much of Venice, the water is licking at the top step, of most buildings, and any storm can bring it lapping at the door.
Winter brings an end to the melting, but allows another dusting of ash.
1600
Venice is Abandoned. And the last summer storm brought the water over the banks of the Thames and flooded half of London, the water just keeps rising, dikes 20 feet high, built just 10~15 years ago are now over flowing during storms, Thousands of Farmers have been forced off their shoreline farms,
1625
Most of the Glaciers on Iceland are gone, either washed away by the rising water, or melted by the new Volcanoes, caused by the rebounding land. Most of the attempts at dike building have been abandoned. The Forest of Holland, lovingly nurtured and protected for hundreds of years are gone, ruthlessly cut down to build ships. Thousands are being carried to the Dutch East Indies. Thousands of others are streaming into New Amsterdam or Reclife in the Americas. Most of the Danes are gone, their Forest went the same way, thro most of them simply moved to the Norway half of their country. Along the Don river the water has been rising, now it carries over its bank and runs down the Volga, faster than any flood , cutting a Channel over ten miles wide. Millions of Indians from the Ganges are flooding north into Himalayas, While their countrymen on the Indus as doing the same into Pakistan, and Afghanistan.
1650
The Japanese here didn’t close themselves of in 1640 OTL, instead they Conquered Korea, they are moving across the Sea of Japan, returning to the land they first left 3.000 years before, others are crossing to Asia where the rising Amur River is forming into a Strait.
The Chinese are moving south into the Himalayas, and west into Tibet,
The French have moved into the Alps, overwhelming the Swiss, by sheer numbers. Except for a few Scots in their Highlands, and Irish in their Hills, England is empty, having arrived on the American shore, from Labrador to Texas, they keep going into the Catskills, Appalachians and Ozarks.
The Gulf of Ababa had been creeping northward over and around, the high ground in its way, now it had breached the last hill, rolling down the slope to the Dead Sea 1500 feet below.
1675
The melting was slowing, mostly because most of the ice was Gone, over the next 25 years the level would rise another 25 feet, but most of that would come from Greenland, as the new warmth pushed and the new water level pulled at the Cap. By 1700 it would be over, and the new nations would slowly come to terms with the great change in their world. There would be new powers, Winners and Losers, and it would be years before it was clear which was which.
