Personally, I worry about a lot. Global warming, not so much. It will have an impact on coasta cities but that aside, it really isn't that big a deal. We have much bigger risks to worry about (both environmental and otherwise).
then again this is one reinforcing feedback loop among several others.
Are you familiar with the concept of planet albedo, and how it is changing on earth due to melting polar cap? Ever heard of ocean's anoxic events and their consequences ?
And the list goes on.
The reason I'm citing this is not because I think we shouldn't worry, but because if the methane is released (and this depends on the release speed as well) we might have a period with an atmosphere with high concentrations of methane, then a sudden reduction.
Runaway greenhouse gas concentrations and higher temperature might trigger (the reason being we know some things, but we don't know everything) a runaway CO2 capture process. It sounds SciFi, and it probably is, and it seems Nitrogen is a limiting factor. But I wouldn't say it is impossible. Or it could be possible with human help.
Then at the end of this period we could end up with less CO2 in the atmosphere, with oil running out and the clathrates emptied.
So on one hand expect large scale migrations and/or massively expensive programs to mitigate the problems. On the other hand expect far more extreme weather far inland.
The idea it will only affect coastal cities is a dangerous one.
There are some cities (New Orleans, Venice, Boston to an extent, to name a few), which are highly vulnerable to sea level rise, but most coastal cities are at high enough elevation that a sea level rise of a few meters wouldn't be the end of the world - it would require better levees, dikes, etc.
Contrast with such risks as increased capability of biological warfare, the persistent risk of nuclear warfare, or, ecologically, declining natural forestation and vegetation due to heavy use of land for cultivated agriculture.
As for extreme weather, it's not like the Earth naturally has less extreme weather at colder temperatures. Warmer temperatures will cause changes in weather patterns, and some places are getting more extreme weather than before, but there is no reason it will be net worse for the whole world.
A lot of cities face issues with follow on effects like that.
It won't be 'the end of the world' if its just a few meters, but it is still enough that cities like London face multi billion flood defence upgrades, and towns housing hundreds of thousands will face increased flood risks as a consequence of anything done to upgrade the defences.
And you're severely underestimating the direct damage. Many of the highest population density areas in the world are at risk,and many of the areas at worst risk are also among the poorest, like Bangladesh.
As for extreme weather, yes indications are that we're heading for more overall extreme weather, not just changes.
Inform yourself and learn that one of the current issue we face is a continental increase of temperature and shift inseason that would make agriculture impossible in about 50 years.
There are reinforcing feedback loops that will push the change past a threshold where cascading effects would make life on earth surface near impossible.
Life on earth is a complex interdependent system and the larger animals are the first to go, guess what's next now that elephants, whales, tigers, and pretty much every animal larger than humans is on the brink of extinction.