How are rising sea levels at the present time evidence of global warming?

Please read my entire post before answering; and no offense, but please don't answer if you can't provide scientific detail at least equal to the small, basic amount I've used. First of all, I just want to say I don't consider myself a global warming denier. I don't think there's enough... show more Please read my entire post before answering; and no offense, but please don't answer if you can't provide scientific detail at least equal to the small, basic amount I've used.

First of all, I just want to say I don't consider myself a global warming denier. I don't think there's enough evidence to definitively say that Earth is either warming or not warming at an abnormal rate. It's fact that Earth's average temperature has risen between one and two degrees Fahrenheit since 1900. However, it's also fact that Earth is in a continuous cycle of natural warming and cooling, and fossil evidence indicates that Earth has been both many times warmer and cooler than it is now during its existence, long before the mass emission of greenhouse gasses. And while the Greenhouse Effect is a plausible theory and likely occurring, it remains unproven because it's impossible to construct a scientific experiment on a scale large enough to produce reliable data. So, I don't think it's possible to absolutely confirm or deny that Earth is warming faster than it should. I just wanted to make it clear that I'm not a blind denier.

Now, my question. Many say that sea levels have already risen as a result of global warming due to melting ice sheets at and near the poles. I'm curious as to how this can occur universally if the temperatures in these areas are still minus forty to minus eighty degrees Fahrenheit during the warmest part of the year. I understand that climate change causes changes in the direction of ocean currents, which in turn cause sea ice to melt. However, anyone who's had a little chemistry knows that the melting of any amount of floating ice wouldn't cause sea levels to rise significantly (negligible increase would result from factors such as thermal expansion), because its displacement is roughly the same whether in the solid or liquid state. The significant rise in sea level would come from the melting of ice sheets currently resting on land. But as I previously mentioned, none of the largest land ice formations have been exposed to temperatures anywhere near freezing long enough for noticeable melting during the last century despite the rise in average world temperature, and land ice for the most part wouldn't be subject to direct influence from ocean currents.

So if melting sea ice doesn't contribute to sea level rise and land ice can't be significantly melting yet, how can a recorded rise in sea level already be linked to the one-two degree increase?

Again, no offense, but if my reasoning is incorrect, I welcome your corrections but please be able to provide some basic scientific reasoning of your own. "Common sense" reasoning as I've heard it used in the past on this subject isn't valid and is usually wrong by nature.
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