The most recent instance of global warming in Earth's history occurred 304 million years ago, during the Late Paleozoic Ice Age (which lasted from 340 to 290 million years ago). Studies have found evidence of rising sea surface temperatures, a retreat of the continental ice cap, and land inundation from oceanic habitats at the period.

In study that was published in Geology, Dr. Liuwen Xia of Nanjing University in China and colleagues investigated the impact of a significant injection of methane from alkaline lakes (pH 9 to 12) into the atmosphere.

Because methane is a powerful greenhouse gas that traps heat 28 times better than carbon dioxide over a century, it is present in large quantities in the atmosphere and contributes to global warming. Understanding the environmental factors that enable methane-producing bacteria to not only survive but also grow is crucial for understanding climate change because they are responsible for 74% of the world's methane emissions.

Methane levels produced by microbial activity were measured in order to study the Junggar Basin in northwest China. In order to identify the type of carbon present and its origin from aquatic green algae, cyanobacteria (photosynthesising microorganisms), and Halophilic Archaea (an extreme microorganism that lives in high salt environments), the researchers took core samples from the lake bed and conducted chemical analyses of the rock.

The algae, cyanobacteria, and archaea preferentially take up the lighter form (carbon-12) when the lake has more dissolved inorganic carbon (a form without carbon and hydrogen bonds), which means the heavier carbon-13 stays in the lake water and is deposited, resulting in distinct differences in the measurements taken from the rock.

Alkalophilic Methanogenic Archaea were shown to have a competitive edge in the low-sulfate, anoxic lake environment, keeping the highest carbon-13 values in the rock, according to the study's findings. This species flourished by creating copious amounts of methane in the lake water, which it subsequently released into the atmosphere in order to get the energy needed for growth. It has been estimated that methane emissions from microbial activity alone might have reached 2.1 gigatons.

By becoming bicarbonate and carbonate (forms of dissolved inorganic carbon), carbon dioxide that was produced by volcanic activity and hydrothermal processes and transported to the lake was noted to enhance the production of methane as it encourages microbial activity. Algae, cyanobacteria, and archaea can virtually always get the carbon they need for their metabolic processes from dissolved inorganic carbon.

Linking this steady increase in methane supply to the Late Paleozoic Ice Age, when atmospheric methane levels peaked 304 million years ago, may therefore imply that the combined contribution from many alkaline lakes around the world may have had a significant effect on global greenhouse gas levels. According to the researchers, methane emissions from just the lakes in northwest China may have reached 109 gigatonnes, which is equal to up to 7521 gigatonnes of carbon dioxide's greenhouse-forcing power.

This clearly demonstrates the impact of methane on our climate, and in particular, the significance of finding alkaline lakes around the world in order to track their present emissions and develop countermeasures. This may involve raising the acidity of the lakes' pH, adding specific kinds of clay, or even dredging the lake bottom, all of which have a variety of unavoidable negative impacts on the environment. As a result, it's possible that there isn't yet a clear solution for lowering lake methane emissions and minimizing their potential to cause global warming.