What they're trying to convey is that human activities greatly affects the rate of the cyclical change of the Earth's climate. CO2 may be beneficial to all living things, yes, but doesn't CO2 contributes to the Greenhouse Effect? If more and more CO2 are trapped in our atmosphere, the possibility is that the temperature of the planet may increase and result to a much faster ice meltdown, which may cause the ocean level to rise (not that much, though).
You are right CO2 emission may contribute to the Greenhouse Effect : "Greenhouse gases—including most diatomic gases with two different atoms (such as carbon monoxide, CO) and all gases with three or more atoms—are able to absorb and emit infrared radiation"
But "if an ideal thermally conductive blackbody were the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C" so hopefully we have the Greenhouse effect
I don't see any evidence that a rise of a few degrees of the temperature will not be beneficial overall; a significant raise of the ocean level is not a reasonable consequence of a small rise in temperature
Sea level has varied widely over timeframes in terms of millions of years, i would imagine it will continue to. Man has located many huge cities right next to the oceans, thus creating something of an economic problem if in the vicinity of those cities, sea levels were to rise on a scale faster than the rebuilding and renewing of the city infrastructure. But that's a multi hundred year timeframe.
The idea that is being promoted by governments, that taxpayers give them money and they will roll back the oceans, is utterly ridiculous.
