If the North and South Poles' ice melted instantly, what would be the effect on humans and other animals? Would the sea creatures thrive? Would a lot of land get covered by water?
Well, the first effect is the temperature on the earth would drop significantly. It takes a lot of energy to melt the ice on the planet, and if it comes from the atmosphere, you get a massive drop in temperatures. (Find that here.)
Second effect...yes the water levels would rise. The north pole is mostly sea ice and this would have little effect on ocean water as the ice displaces the same amount the melted water would. The south pole melting would increase sea levels by around 200-300 feet (pending study you want to accept). Most of humanity does in fact live close to the ocean...a country like Bangledesh goes 47% underwater (that's the highest population density country on the planet). This is around 1/4 of the American population under water as well.
Sea creatures won't necessarily thrive. Most of them have adapted to the salt water concentrations they are used to and a quick adjustment stands to harm them. Otherwise, unless there is something fundamentally helpful (delicious?) for them to take on land, it wouldn't have much a difference. As a more scary alternative, certain nuclear power generation sites could be submerged, potentially flooding the nearby water with radiation.
Your worst case scenario is if this sudden increase in fresh water alters the current (great oceanic conveyor belt if you will). This is the cycle of heat throughout the ocean...certain areas (Europe primarily) remain temperate by warmer tropical currents cycling water to the northern regions. If this cycle was to falter, England would likely freeze over.
Most of these points here are answers to much more specific versions of this question on Worldbuilding.
The ice near the North Pole is floating, so no sea level rise would result from that. The South Pole melt would only have an effect if it reached the ocean. If it was a sea near the South Pole, no effect either.
If you melt all the ice caps on Greenland and Antarctica, a significant sea rise would occur. Usually numbers like 200 feet are quoted.
If the North and South Poles' ice melted instantly, what would be the effect on humans and other animals?
- Humans would be in a bit of trouble as a significant portion of the worlds arable land would be under water. If this all happened at once with no warning that may not be terribly detrimental as the bulk of the world's population would be dead...so thats good.
- Land animals would be similarly in trouble as entire habitats and species would be completely wiped out.
Would the sea creatures thrive?
- Maybe in the long run, the rapid changes to temperature and ocean depth would wreak havoc on ocean environments. Reefs would be in water 200-300 METERS deeper meaning they would have trouble surviving with their food and light sources no longer being available. Similar to land based animals there would be a great upheaval and mass extinctions most likely. In the long run marine life would bounce back, there would likely be a significant increase in algae and other simple water life with the reduction in the numbers of predators. Ocean animals would definitely be the first to bounce back though.
Would a lot of land get covered by water?
- See the map link Vincent provided, its an excellent resource
Some additional notes
- Every communist nation would be either A. Underwater or B. Decimated
- Northern Europe is totally hosed...water joke for you there.
- The US East coast is now an island
- Russia is essentially gone, only the sparsely populated west would remain
- Africa becomes the center of the world as it is the least impacted by the water level rise, its hard to predict how the weather pattern would end up but if you assume the continent gets more moisture in the north it would end up being the population center of the world.
- The pacific rim...more of a lip now
- Japan survives surprisingly well landmass wise
Eventually a new balance would be achieved of course, nature is skilled like that.
Beyond sea level increase, also weather patters will drastically change. After melting Greenland's glaciers, less dense fresh water would stop Gulf Stream which transfers heat from equatorial Atlantic to Europe. Europe would go colder (decrease of agriculture) and hurricanes would get stronger.
Melting permafrost in northern tundra's of Canada, Alaska and Siberia will release huge amounts of methane, which is very potent greenhouse gas (more than CO2) which will increase greenhouse effect.
Salinity of water would not change significantly (amount of added fresh water is small).