Global warming is perhaps not the best term for what seems to be happening. Global climate change might be a better name for it. Changing weather patterns will bring about local ups and downs on a temporary basis, but the general trend, over a longer time scale, is what the concern is about.
There will always be those who will argue, even with hard facts, but there can be little, or no, doubt that polar ice is diminishing and sea level is rising, but, of course, it has all happened before, so those with a vested interest in activities which increase our carbon footprint have plenty of scope for argument.

There never was nothing.