Eocene Thermal Maximum 2

Eocene Thermal Maximum 2 (ETM-2), also called H-1 or the Elmo (Eocene Layer of Mysterious Origin) event, was a transient period of global warming that occurred around either 54.09 Ma or 53.69 Ma. It appears to be the second major hyperthermal that punctuated the long-term warming trend from the Late Paleocene through the Early Eocene (58 to 50 Ma).

The hyperthermals were geologically brief time intervals (<200,000 years) of global warming and massive input of isotopically light carbon into the atmosphere. 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 55.5 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. In any case, the hyperthermals appear to have ushered in the Early Eocene Climatic Optimum, the warmest sustained interval of the Cenozoic Era. They also definitely precede the Azolla event at about 49 Ma.