From NASA,

In 1824, Joseph Fourier calculated that an Earth-sized planet, at our distance from the Sun, ought to be much colder. He suggested something in the atmosphere must be acting like an insulating blanket.

In 1856, Eunice Foote discovered that blanket, showing that carbon dioxide and water vapor in Earth’s atmosphere trap escaping infrared (heat) radiation.

In the 1860s, physicist JohnTyndall recognized Earth’s natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations.

In 1896, a paper by Swedish scientist Svante Arrhenius first predicted that changes in atmospheric carbon dioxide levels could substantially alter the surface temperature through the greenhouse effect.

In 1938, Guy Callendar connected carbon dioxide increases in Earth’s atmosphere to global warming.

In 1941, Milutin Milankovic linked ice ages to Earth’s orbital characteristics. 

In 1956, Gilbert Plass formulated the Carbon Dioxide Theory of Climate Change.

At the end of July, 40% of the 4,000-year-old Milne Ice Shelf, located on the north-western edge of Ellesmere Island, calved into the sea. Canada’s last fully intact ice shelf was no more.

On the other side of the island, the most northerly in Canada, the St Patrick’s Bay ice caps completely disappeared. Two weeks later, scientists concluded that the Greenland Ice Sheet may have already passed the point of no return. Annual snowfall is no longer enough to replenish the snow and ice loss during summer melting of the territory’s 234 glaciers. Last year, the ice sheet lost a record amount of ice, equivalent to 1 million metric tons every minute.

The Arctic is unravelling. And it’s happening faster than anyone could have imagined just a few decades ago. Northern Siberia and the Canadian Arctic are now warming three times faster than the rest of the world. In the past decade, Arctic temperatures have increased by nearly 1C. If greenhouse gas emissions stay on the same trajectory, we can expect the north to have warmed by 4C year-round by the middle of the century.

FROM USGS, an official US Government website:
How would sea level change if all glaciers melted?

There is still some uncertainty about the full volume of glaciers and ice caps on Earth, but if all of them were to melt, global sea level would rise approximately 70 meters (approximately 230 feet), flooding every coastal city on the planet.