It appears that the threat is quite real and overwhelmingly agreed upon by those who devote their lives studying the details of this issue. It's empirically true that greenhouse gas levels are at levels not seen in literally hundreds of thousands of years (specifically carbon dioxide), and this will impact ocean levels, the ocean food chain, storms formation, seasonal patterns, animal migration, farmland use, etc.
The Earth has always had periods of global warming and global cooling. We as a species are just speeding up the process of the global warming and cooling. These trends in the weather are only the natural way of the Earth. So we can choose to speed up the process or slow it down. That is up to you.
No, greenhouse gases are not as big of a deal as scientists are making them out to be, because greenhouse gases do not have a large impact on the environment. Compared to the rest of the universe, humans are small and insignificant. Humans only wish that they could control the world. What humans do does not make a big difference.