When begins the Anthropocene?

The Anthropecene is the geological pewriod when the impact of human becomes desproportionately high. It has been proposed to characterize the present period, with widespread alteration ofg the environment, climate change, imission of radionucldies in the atmosphere. Although the idea begins to be generally accepted, the main problem is when? If the anthropocen has to be an actual geological period and not only a loose word, it must defined precisely in the same way as, for instance, the Pleistocene or the Cretaceous. In an unusually long paper on nature  the author discusses three ideas: the discovery of the Americas, with borad floristic and faunal exchange among the continents, the onset of the industrial revolution or the beginning of atomic testing with rise of redionuclides in the atmosphere. Now a report f5rom WWE suggests another idea: the Anthropiocen has not yet begun. In the next few year, according to recent data, most vertebrates will vanish, with  mass extinction anlagous to that marking the Permian-Triassic border or the Cretaceous-Paleocene. Is 2020 the date of the actual beginning of the Anthropocene?