What happens in one city in one month is only a very very small part of the picture. You can make very little inference on global warming based on the weather in one city in one month.
You can make a little more inference on global warming based on the weather around the world in one month.
And we can say a lot about global warming based on the world's weather over a 30-year period.
A lot of heat got released from the ocean last year in the El Niño event: heat that had been accumulating in the oceans for a few years. That heat is now getting distributed around the world, which is why we're seeing rises in global surface temperatures - a similar thing happened back in 1997/8. The Earth has been accumulating a lot of heat for years, and it's now showing up as rises in surface temperatures.
The accumulation of heat is happening because the Earth has been absorbing more energy than it has been radiating away into space. That has happened because of human emissions of greenhouse gases, in particular, but not exclusively, carbon dioxide and methane.
Unnatural global warming started decades ago. Now, it's accelerating.