Английская Википедия:Early Eocene Climatic Optimum

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The Early Eocene Climatic Optimum (EECO), also referred to as the Early Eocene Thermal Maximum (EETM), was a period of extremely warm greenhouse climatic conditions during the Eocene epoch. The EECO represented the hottest sustained interval of the Cenozoic era and one of the hottest periods in all of Earth's history.

Duration

The EECO lasted from about 54 to 49 Ma. The EECO's onset is signified by a major geochemical enrichment in isotopically light carbon, commonly known as a negative δ¹³C excursion, that demarcates the hyperthermal Eocene Thermal Maximum 3 (ETM3).

Climate

Following some climate models, the EECO was marked by an extremely high global mean surface temperature, which has been estimated to be anywhere between 23.2 and 29.7 °C, with the mean estimate being around 27.0 °C. In North America, the mean annual temperature was 23.0 °C. The mean annual temperature range (MATR) of North America may have been as low as 47 °C or as high as 61 °C, while the MATR of Asia was anywhere from 51 to 60 °C. Clumped isotope measurements from the Green River Basin confirm a high seasonality of temperature, contradicting climatological predictions of an equable climate under greenhouse conditions. Mean annual precipitation (MAP) in North America was about 1500 mm. Sediments from San Diego County, California record a MAP of 1100 ± 299 mm, notably drier than the region was during the Palaeocene-Eocene Thermal Maximum. The high elevation areas of Asia, Africa, and Antarctica saw elevation dependent warming (EDW), while those in North America and India saw elevation dependent cooling (EDC).

Although sea surface temperatures (SSTs) are often believed to have had a shallow latitudinal temperature gradient, this is likely to be an artefact of burial-induced oxygen isotope reequilibration in fossilised benthic foraminifera.

Climate modelling simulations point to a carbon dioxide concentration in the atmosphere of about 1,680 ppm to reproduce the observed hothouse conditions of the EECO, although geochemical proxies suggest only 700-900 ppm. Additionally, methane concentrations in the Early Eocene may have been significantly higher than in the present day.

Causes

The EECO was preceded by a major long-term warming trend in the Late Palaeocene and Early Eocene. It was initiated by a series of intense hyperthermal events in the Early Eocene, including Eocene Thermal Maximum 2 (ETM2) and ETM3.

The emplacement of the Pana Formation, a volcanic rock formation in southern Tibet that may represent the product of a supereruption, has also been proposed as a source of excess carbon flux into the atmosphere that drove the EECO.

Biotic effects

The final phase of the Angiosperm Terrestrial Revolution occurred during the EECO. The supergreenhouse climate of the EECO fostered extensive floral diversification and increased habitat complexity in North American terrestrial biomes.

In South America, the EECO coincided with the Itaboraian South American Land Mammal Age. Cingulates diversified over the course of the EECO.

The euryhaline dinoflagellate Homotryblium became superabundant at the site of Waipara in New Zealand during the early and middle EECO, reflecting the occurrence of significant stratification of surficial waters as well as increased salinity.

Comparison to present global warming

Because the pCO₂ values of the EECO could potentially be reached if anthropogenic greenhouse gas emissions continue unabated for three centuries, the EECO has been used as an analogue for high-end projections of the Earth's future climate that would result from humanity's burning of fossil fuels. Based on the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2150 CE, the climates across much of the world would resemble conditions during the EECO.

See also

• Palaeocene-Eocene Thermal Maximum
• Middle Eocene Climatic Optimum
• Middle Miocene Climatic Optimum
• Middle Pliocene Warm Period