When Erin First Rose

"When Erin first rose from the dark swelling flood,

God bless'd the green island and saw it was good;

The emerald of Europe, it sparkled and shone

In the ring of the world the most precious stone.

In her sun, in her soil, in her station thrice blest,

With her back towards Britain, her face to the West,

Erin stands proudly insular, on her steep shore,

And strikes her high harp 'mid the ocean's deep roar."

(http://www.libraryireland.com/CIL/DrennanErin.php)

It was poet, physician and political radical, William Brennan who coined the term "Emerald Isle" in his poem dedicated to Ireland called When Erin First Rose written in 1795.  Its verdure does not come from its deep forests for they were removed in the massive clearing efforts of the 1600's.  The deep green shade comes from Ireland's lush green grass thanks to its wet climate.  While Ireland is on the latitude of Newfoundland, which receives plenty of snow in the winter, Ireland benefits from the North Atlantic Drift which pushes the warm gulf stream towards the isle, keeping the temperature above freezing. Annual rainfall along the west coast can exceed 120 inches.  The abundance of lush grass is a perfect place for livestock to graze.  In fact, Ireland's eight million sheep and seven million cows outnumber its four and a half million people. (http://wonderopolis.org/wonder/where-is-the-emerald-isle)  

http://www.irishcentral.com/roots/history/how-did-ireland-come-to-be-called-the-emerald-isle