Islands come and go all the time - geologically speaking. That has always been, and most likely always will be, the case. The erosion and disappearance of delta islands especially, is quite common. For one famous example, the swampy low-lying islands at the mouth of the Mississippi river have been disappearing for decades, but their disappearance has nothing to do with rising sea levels (levels, by the way, which have risen by approximately 1 inch in the past 150 years). They are disappearing because the natural processes which build them up against the constant erosion of current and waves has been altered by humanity's need to control flooding in those areas. When the floods stop depositing new layers of sediment, the constant erosion eventually wins out and they slip back beneath the waves altogether. Many $Billions have been spent to attempt to reverse that process, while simultaneously maintaining the desirable flood-control features, but success has been somewhat limited so far.
As for the broader question of Global Warming, I don't think anyone disputes the fact that the world is a little warmer than it was 35 years ago - when many of the same scientists who today screech about warming were earnestly warning us of the impending ice age. But the current warming trend started in the early to mid 1800s, when humanity was a mere pimple on an elephant's posterior. In fact, most of the post-1840 warming happened before 1940, when humanity's carbon emissions were a trifling small fraction of what they are today.
Same goes for the glacial retreat the warmists get so shrill about. Periodic surveys of the glaciers in Glacier National Park showed that the glaciers there lost roughly 50% of their mass between 1870 and 1910 - some more, some less, but all lost significant mass.
Do a little research to verify my statements above, then ask yourslef: If the globe started to warm almost 100 years prior to the beggining of our modern age, how can the carbon emissions associated with our modern age possibly be the primary cause?
That is one of the major questions the promoters of Man-Made Global Warming have either been unable or steadfastly unwilling to answer, while simultaneously insisting that we must put our faith in their computer models. Their computer models have been proven unreliable over 5, 10 and 15 year periods, but we are told that those models are akin to Revealed Truth over multi-century time horizons!?! Such silliness cannot be taken seriously, yet we are told to BUY NOW, before it's too late.
Another of the major quesitons which the promoters of Man-Made Global Warming have vigorously avoided is how humanity caused the dozens, if not hundreds, of similar warming and cooling spells throughout geological history. The island of Manhattan, for one well-known example, has at various times in geologic history been burined under several thousand feet of glacial ice for a spell, then warmer than the tropics are today for a spell, then back under the ice for a millenia, then back to the tropics, and so on. Humans did not even exist on this planet for most of those cycles, so how cane a rational person believe that we are driving the changes this time? The fact that so many do believe in such a weak theory is a triumph of marketing over reason.
Lastly, the biggest question the promoters of Man-Made Global Warming will never answer or debate is, on balance, would humanity be better off with temperatures a little warmer than they are today? I know you've seen the Hollywood version of warmer temperatures causing sudden and massive calamaties, but that is not the way it works in the real world. In reality, such changes take place over multiple centuries. Will there be some draw-backs? Certainly. But might the benefits more than outweigh the problems? Would it be such an awful thing if, 200 years from now, the northern plains of Canada and Russia were open to agricultural development; if we could grow Citrus in the central plains of the U.S.; if Virginia was as warm as South Carolina is today; if trees and other plants grew faster; if the shipping lanes of the Northwest Passage were open for several months every year; etc, etc, etc. The alarmists want us to focus on the threats of all the bad things which might happen if we don't give them tens of $Trillions and immense power over the life-style choices of every human, but they will never engage in a rational discussion of the potential benefits of a warmer climate. IF their worst-case scenarios come to pass, we will certainly lose some low-lying coastal land, but we will gain millions of acres which are now locked in permafrost.