Transient period of global warming that occurred approximately 54 million years ago
Eocene Thermal Maximum 2 (ETM-2), also called H-1 or Elmo (Eocene Layer of Mysterious Origin), was a transient period of global warming that occurred around 54 Ma.[1][2][3][4][5] It was the second major hyperthermal that punctuated long-term warming from the Late Paleocene through the Early Eocene (58 to 50 Ma).[6]
The hyperthermals were geologically brief time intervals (<200,000 years) of global warming and massive input of isotopically light carbon into the ocean and atmosphere.[7][8] The most extreme and best-studied event, the Paleocene-Eocene Thermal Maximum (PETM or ETM-1), occurred about 1.8 million years before ETM-2, at approximately 55.8 Ma. Other hyperthermals likely followed ETM-2 at nominally 53.6 Ma (H-2), 53.3 (I-1), 53.2 (I-2) and 52.8 Ma (informally called K, X or ETM-3). The number, nomenclature, absolute ages and relative global impact of the Eocene hyperthermals are the source of much current research.[9][10]
In any case, the hyperthermals appear to have ushered in the Early Eocene Climatic Optimum, the warmest sustained interval of the Cenozoic Era.[11] They also definitely precede the Azolla event at about 49 Ma.
^Slotnick, B.S.; Dickens. G.R.; Nicolo, M.J.; Hollis, C.J.; Crampton, J.S.; Zachos, J.C.; Sluijs, A. (2012). "Large amplitude variations in carbon cycling and terrestrial weathering during the latest Paleocene and earliest Eocene: The record at Mead Stream, New Zealand". Journal of Geology. 120 (5): 487–505. Bibcode:2012JG....120..487S. doi:10.1086/666743. hdl:1911/88269. S2CID55327247.