Isn't it really cold?

Yes -- riding in the Winter is cold.  I wear long johns, strong wind resistant mittens, a balaclava (facemask), and two layers of long sleeves.  When I first step outside I am cold and it is just ready to get riding.  Once I get about 5 minutes in, my legs are moving, and my body is really starting to warm up.  On the really cold days, my face does get cold.  

Yes -- riding in the Summer is hot.  

Isn't it dangerous?  New York streets are scary for bikers!

It is historically true that New York City is a dangerous place to be a cyclist, but New York is much different when it comes to cycling than it has been in the past.  Miles of bike lanes, protected lanes, buffered lanes, and greenways have been added to the city's network allowing for some rides in the city to not be in conflict with car traffic at all.  Cycling has taken off as a form of transportation for people across the United States and New York City has been one of the leaders in new ideas about cycling in the city and how infrastructure can accommodate those new ideas.  

That said, there are parts of the city that are always going to be a challenge to get through, whether it is on foot, in a car, or on a bike.  Much of Midtown Manhattan and areas nearest highways in the outer boroughs, among other areas, are still places that require a bit more attention and care when riding through them.  If these areas can be avoided, this is best.  If you need to cycle through these areas, plan your route out carefully, and plan out your moves through tough intersections.