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.