Prime Minister Katrin Jakobsdottir, Environment Minister Gudmundur Ingi Gudbrandsson and former Irish President Mary Robinson took part in the commemoration ceremony.
In 1890, Okjokull covered 16 square kilometers (6.2 square miles) of glacier ice but by 2012, it measured just 0.7 square kilometers.
In 2014, Iceland declared it the first glacier to disappear in the country. This monument must recognize that we know what is happening and know what needs to be done. "Only you know if we did it", the plaque reads.
It's easy to get lost in the numbers like Iceland loses about 11 billion tonnes of ice per year, and though glaciers cover about 11% of the country's surface and are used for renewable energy systems, scientists expect all 400-plus glaciers to be gone by 2200.
Scientists bid farewell to Okjökull, the first Icelandic glacier lost to climate change.
The melted glacier was the subject of the 2018 documentary "Not Ok", produced by anthropologists Cymene Howe and Dominic Boyer of Rice University in the USA state of Texas, who initiated the monument project.
With poetry, moments of silence and political speeches about the urgent need to fight climate change, Icelandic officials, activists and others said their official goodbyes to what once was the handsome glacier of Okjökull.
Howe said that memorializing a lost glacier emphasizes what is being lost and disappearing all over the world. "Perhaps a monument to a lost glacier is a better way to fully grasp what we now face".
One of the mourners was 17-year-old Gunnhildur Hallgrimsdottir. They are also the producers of 'Not Ok, ' a documentary on the Okjokull glacier.
In 2014, "we made the decision that this was no longer a living glacier, it was only dead ice, it was not moving", Oddur Sigurdsson, a glaciologist with the Icelandic Meteorological Office, told AFP.
"The conversation about climate change can be very abstract, with many devastating statistics and sophisticated scientific models that may feel incomprehensible".