The changing climate is a reality that comes to be the defining issue of our time. While carbon emissions and rising temperatures have dominated the discourse on climate change, little focus is given to understand the response of microbes—tiny organisms that support the existence of all higher life forms—to climate change. These elusive creatures constituting the life support system of the biosphere have been mainly overlooked in the context of climate change—in both scientific and policy development forums.

More than 30 microbiologists signed a statement published in Nature Reviews Microbiology on June 18, 2019, admonishing the risk of ignoring these organisms. In the report titled Scientists’ warning to humanity: microorganisms and climate change the microbiologists stated that changes in microbial biodiversity and activities would affect the resilience of all other organisms, and hence their ability to respond to climate change. ‘Microbes are themselves also profoundly affected by climate change, but are rarely the focus of climate change research, education, and policy,’ says Britt Koskella, an evolutionary biologist and assistant professor of integrative biology at UC Berkeley who collaborated on the consensus statement. With the consensus statement, scientists anticipate raising awareness about the role and vulnerability of microbes and are calling for the inclusion of microorganisms in climate change research.

How does climate change affect microbes?

Climate change can influence, both directly and indirectly, the structure and diversity of microbes through multiple intertwined factors such as temperature, precipitation, soil properties, and plant input. For example, ocean acidification exposes marine microbes to a pH level that is well beyond their historical range, consequently affecting their intracellular balance system. Scientists posit that lower pH causes bacteria and archaea to change their gene expression to support cell maintenance rather than growth. Moreover, various studies have been conducted to assess the effects of elevated temperature on microbial respiration rate as well as mechanisms and outcomes of adaptation. A study conducted by Roberto Danovaro revealed that the seabed microbes thrive in cold water, and their population plummets noticeably when the ocean water warms. Warmer deep-sea ecosystems possess a low substrate of organic carbon supplied from the surface water, causing the decline. Furthermore, as the temperature increases so do the metabolic rate of microbes, demanding more food for survival, thus the shortage of food in the deep-seabed supports fewer individual microbes. Besides these, because of climate change, the biodiversity of microscopic organisms is declining, which in turn is causing the decline of host-specific microbes’ diversity.

Various microbial groups are specific to a certain temperature range for their growth and activity, and global warming has a profound impact on the composition of such microbial community. A research conducted in the arid soil of the USA, for instance, revealed that, as global temperatures soar, heat-tolerant bacteria outcompete and even supplant the bacteria that would thrive at lower temperatures. Both kinds of bacteria are critical in maintaining the microbial population in the topsoil and controlling soil erosion. Global warming, however, is causing the relative abundance of one type of bacteria, thereby affecting the regulation of specific processes driven by these organisms.

How do microbes affect climate change?

Microbes are the critical component of carbon and nitrogen cycles and are involved in the emission and removal of greenhouse gases like carbon dioxide and methane. Studies have shown that, through the decomposition of organic matter, microbes in soil emit 55 billion tons of carbon dioxide every year, which accounts eightfold more than that by a human. Most importantly, microbial organic matter decomposition is climate-sensitive. The permafrost, one of the most significant reservoirs of carbon in the Earth, harbours a myriad of inactive microbial communities. Global warming has melted the permafrost and activated the dormant microbial community. With the intensified thawing, the degradation of microbial organic matter has accelerated, releasing a higher amount of carbon dioxide and methane gas.

The critical issue, today, is how the change in the microbial diversity triggered by climate change affects the survival of humankind. Microbes play a central role in the biogeochemical cycle, plant productivity, and human health. Variations in microbial diversity, therefore, undoubtedly affect the biogeochemical cycles, agricultural productivity, and human health. Different studies have shown that climate change affects the viability and virulence of pathogenic microbes. A sharp spike in West Nile virus infections in Europe in recent years, severe outbreaks of dengue in more than 100 countries, and an outbreak of anthrax in northern Russia from a 75-year-old caribou carcass thawing out substantiate the findings of such studies.

Furthermore, the spread of crop diseases has brutally threatened global food security. These events foretell the bleak future of humankind, especially if microorganisms are downplayed in climate change research and policy development forums.

The greatest irony is that we worry more about the dire consequences of climate change on polar bears, which have a relatively insignificant role in supporting life in the biosphere as compared to microbes. It is high time we shifted our focus to the ‘unseen majority’ of the Earth. Neglecting these elusive yet influential creatures of the biosphere in climate change research and policy development would only lead to the decimation of humanity. Understanding how microorganisms respond to the changing climate is critical for developing new avenues of climate change adaptation and mitigation strategies. Microbes should, therefore, be considered in policy development and integrated into climate models. 

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