What happens if all the icebergs melt?

Answer 1

sea levels will rise which will cause flooding to the crustal plates. flooding leads to loss of life, destruction of infrastructure and vegetation

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This is, in part, the wrong question; and that, in turn, stems from a misconception about the difference between icebergs and glaciers.

Icebergs are floating masses of ice in the ocean. As such, their melting would NOT raise sea levels. The same goes for masses of sea ice such as that found in the Northern Polar regions. They already displace a volume of water equal to their weight, such that when they melt, they do not significantly increase the volume of the oceans. Given a large enough volume of melting ice, however, it might locally affect temperature and salinity, which can have an effect on ocean currents (see below for more on that).

Glaciers, on the other hand, are masses of ice on land. The mass of water contained within them is not already part of the ocean. Most glacial masses flow downhill slowly; they also melt/retreat seasonally and are replenished by snowfall (whether they are replenished at the same rate they melt is another matter entirely).

The largest ice sheets (glacial masses that cover more than 50,000 sq. km) exist on Greenland and Antarctica. If those and the major mountain glaciers (such as the ones in the Alps and Himalayas) were to melt, sea levels WOULD rise by several meters.

In addition, if they melted, the coastline flooding, while significant, could be the least of humanity's worries. Temperature and salinity of the oceans at the edge of the ice masses could be drastically affected by the influx of meltwater. This, in turn, could have a major impact on ocean currents. The movie The Day After Tomorrow (over)dramatized this in typical Hollywood fashion.

The theory goes that a major release of fresh cold water into the North Atlantic could disrupt the Thermohaline circulation (also known as the Ocean Conveyor Belt). This current is instrumental in transporting heat north from the equatorial regions. If it were disrupted, a sudden climate shift would follow, potentially involving a new ice age in the (presently) temperate parts of the Northern Hemisphere. Such changes would most likely occur over a matter of years or decades (still terribly sudden in climatic and geological terms), rather than months or weeks as depicted in the movie.

As a matter of fact, there is a significant body of evidence indicating that similar events have occurred in the past. Large influxes of low density meltwater from Lake Agassiz (an immense glacial lake) and deglaciation in North America are thought to have led to a disruption of deep water formation and subsidence in the extreme North Atlantic and caused the climate period in Europe known as the Younger Dryas - a period of intense, dry cold lasting approximately 1300 years.

Some recent experiments with carbon dating of peat cores from Ireland indicate that the Younger Dryas may, in fact, have come on quite suddenly, over a matter of months or a year or two at most.

None of this is predicated one way or the other on whether or not the current spate of warming is human-caused or human-influenced at all. Obviously, humans were not pouring several gigatons per year of extra carbon dioxide and methane into the atmosphere way back before the Younger Dryas. That is NO reason to suppose that we couldn't be influencing the process now.

Bottom line: If all the icebergs/sea ice melt, it sucks for the polar bears and seals but not much else. On the other hand, if those all melt, the chance of major impacts on the ice sheets is high. If the ice sheets start to go, significant sea level rise is probable. If the thermohaline circulation is significantly disrupted, the impacts of our current warming trend are nothing compared to what humanity could face over the next century or two from the onset of a minor ice age. Consider the probable geopolitical impact of the rise in global grain prices from our current drought in North America; now, extend that to include massive crop failures worldwide for decades at a time. A trifle unnerving, no?

Are we looking at the extinction of the human race? Most likely not. Could it cause mass starvation, war, and the collapse of civilization as we know it, to the tune of billions of deaths? Quite possibly. Serious political problems and resource wars worldwide, suffering on a global scale? At the very least.