The unprecedented global increase in greenhouse gases can decrease rainfall in the equatorial region with associated shift and vegetation, and also replace India’s biodiversity hotspots consisting of evergreen forests in the Western Ghats, northeast India and the Andamans into deciduous forests, shows a new study.

Deep time hyperthermal events are considered potential analogs for future climate predictions. However, data of these hyperthermal events are mainly known from the mid- and high latitude regions. However, there is lack of quantitative data from the equatorial or tropical regions.

Researchers from Birbal Sahni institution of Palaeosciences (BSIP), an autonomous institute of Department of Science and Technology, used fossil pollen and carbon isotope data from the Eocene Thermal Maximum 2 (ETM-2), also known as H-1 or Elmo, a period of global warming that occurred around 54 million years ago, to quantify the terrestrial hydrological cycle during that period.

It was during this period that the Indian plate lingered near the equator during its journey from the southern to northern hemisphere.  This makes the Indian plate a perfect natural laboratory that offers a peculiar opportunity to understand the vegetation-climate relationship near the equator during the ETM-2. On the basis of availability of fossils from ETM2, the researchers selected the Panandhro Lignite Mine of Kutch in Gujarat and collected fossil pollen from there.

Analyzing the pollen, they found that when atmospheric carbon dioxide concentration was more than 1000 ppmv near the palaeo-equator, the rainfall decreased significantly, leading to the expansion of deciduous forests.

The study published in the journal Geoscience Frontiers raises important questions about the survival of equatorial/ tropical rainforests and biodiversity hotspots under increased carbon emissions. It can help understanding the relationship between CO₂ and hydrological cycle and aid in the future conservation of biodiversity hotspots.

Fig. 1. The diagram shows the changing patterns of rainfall vis-à-vis vegetation under varying carbon dioxide concentration during the pre-hyperthermal, hyperthermal and post-hyperthermal events of the early Paleogene.

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