Scientists' warning to humanity: microorganisms and climate change

Abstract

In the Anthropocene, in which we now live, climate change is impacting most life on Earth. Microorganisms support the existence of all higher trophic life forms. To understand how humans and other life forms on Earth (including those we are yet to discover) can withstand anthropogenic climate change, it is vital to incorporate knowledge of the microbial 'unseen majority'. We must learn not just how microorganisms affect climate change (including production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. This Consensus Statement documents the central role and global importance of microorganisms in climate change biology. It also puts humanity on notice that the impact of climate change will depend heavily on responses of microorganisms, which are essential for achieving an environmentally sustainable future.

Fig. 1. Microorganisms and climate change in marine and terrestrial biomes.

In marine environments, microbial primary production contributes substantially to CO₂ sequestration. Marine microorganisms also recycle nutrients for use in the marine food web and in the process release CO₂ to the atmosphere. In a broad range of terrestrial environments, microorganisms are the key decomposers of organic matter and release nutrients in the soil for plant growth as well as CO₂ and CH₄ into the atmosphere. Microbial biomass and other organic matter (remnants of plants and animals) are converted to fossil fuels over millions of years. By contrast, burning of fossil fuels liberates greenhouse gases in a small fraction of that time. As a result, the carbon cycle is extremely out of balance, and atmospheric CO₂ levels will continue to rise as long as fossil fuels continue to be burnt. The many effects of human activities, including agriculture, industry, transport, population growth and human consumption, combined with local environmental factors, including soil type and light, greatly influence the complex network of microbial interactions that occur with other microorganisms, plants and animals. These interactions dictate how microorganisms respond to and affect climate change (for example, through greenhouse gas emissions) and how climate change (for example, higher CO₂ levels, warming, and precipitation changes) in turn affect microbial responses. OMZ, oxygen minimum zone.

Fig. 2. Agriculture and other human activities that affect microorganisms.

Agricultural practices influence microbial communities in specific ways. Land usage (for example, plant type) and sources of pollution (for example, fertilizers) perturb microbial community composition and function, thereby altering natural cycles of carbon, nitrogen and phosphorus transformations. Methanogens produce substantial quantities of methane directly from ruminant animals (for example, cattle, sheep and goats) and saturated soils with anaerobic conditions (for example, rice paddies and constructed wetlands). Human activities that cause a reduction in microbial diversity also reduce the capacity for microorganisms to support plant growth.

Fig. 3. Climate change exacerbates the impact of pathogens.

Anthropogenic climate change stresses native life, thereby enabling pathogens to increasingly cause disease. The impact on aquaculture, food-producing animals and crops threatens global food supply. Human activities, such as population growth and transport, combined with climate change increase antibiotic resistance of pathogens and the spread of waterborne and vector-borne pathogens, thereby increasing diseases of humans, other animals and plants.