The issue of global warming is not a recent phenomenon but has occurred repeatedly throughout Earth’s history. One such instance took place 304 million years ago during the Late Paleozoic Ice Age. Researchers have discovered evidence of various alarming changes during this period, including increased sea surface temperature, continental ice decline, and the flooding of oceanic environments onto land. These findings shed light on the significance of understanding past climate change to better comprehend the current situation.
A recent study conducted by Dr. Liuwen Xia and his team at Nanjing University in China focused on the impact of methane emissions from alkaline lakes on global warming. Methane, a potent greenhouse gas, has the ability to trap heat 28 times more effectively than carbon dioxide over a century. Approximately 74% of global methane emissions come from methane-producing microorganisms. Therefore, understanding the environmental conditions that enable these organisms to thrive is crucial for comprehending climate change.
To investigate this further, the researchers turned their attention to the Junggar Basin in northwest China. They analyzed methane levels derived from microbial activity by examining core samples from the lake bed and conducting chemical analyses of the rocks. By determining the type of carbon present, they were able to identify its source, whether from aquatic green algae, cyanobacteria, or halophilic archaea (extreme microorganisms that thrive in high salt environments).
The researchers discovered that a particular type of archaea, known as alkalophilic methanogenic archaea, capitalized on the low sulfate anoxic environmental conditions of the lake. This species preserved the heaviest carbon-13 values in the rock, suggesting its preference for these conditions. By producing large amounts of methane in the lake water, the archaea found the energy required for growth. As a result, significant methane emissions, amounting to up to 2.1 gigatons, were released into the atmosphere through microbial activity alone.
Carbon dioxide, originating from volcanic activity and hydrothermal processes, was transported to the lake. In the lake, it underwent a conversion process into bicarbonate and carbonate forms of dissolved inorganic carbon. This conversion increased the alkalinity of the lake, which promoted microbial activity and, in turn, the creation of methane. The availability of dissolved inorganic carbon served as an abundant source of carbon for the algae, cyanobacteria, and archaea, fueling their metabolic processes.
The link between the increased methane supply and the Late Paleozoic Ice Age, characterized by a methane peak 304 million years ago, raises questions about the collective effect of alkaline lakes worldwide on greenhouse gas levels. The researchers propose that, even considering only the lakes in northwest China, methane emissions could have reached a staggering 109 gigatonnes. To put this in perspective, this amount of methane is equivalent to the greenhouse forcing power of up to 7521 gigatonnes of carbon dioxide.
This study underscores the potency of methane in influencing climate change and emphasizes the critical need to identify and monitor alkaline lakes globally. Finding effective solutions to mitigate their methane emissions is vital. Potential strategies include reducing the pH of the lakes to make them more acidic, incorporating specific types of clay, or dredging the lake bottom. However, each solution introduces its own set of environmental consequences. Consequently, finding a clear and effective approach to reducing methane emissions from alkaline lakes remains a significant challenge.
Our understanding of past global warming events, such as the one that occurred during the Late Paleozoic Ice Age, informs our present-day knowledge of climate change. The research on alkaline lakes and their contribution to methane emissions provides valuable insights into the role of microbial activity in greenhouse gas levels. As we continue to explore potential solutions, it is crucial to strike a delicate balance between mitigating methane emissions and minimizing the environmental impact of those mitigation efforts.