Global warming effects on carbon sinks
Carbon completes its life cycle passing through the oceans, soils, vegetation and atmosphere. In these pathways, carbon is absorbed, stored and released in different processes. This pathway is known as the carbon cycle. The balance of the carbon cycle has made our life possible on earth as we are now. But if the balance of carbon from soil to the atmosphere is disturbed by more emissions, then the carbon cycle becomes imbalanced and affects the whole ecosystem, which is not expected for human welfare, as the ecosystem services and living systems will be partially disturbed or lost.
Nearly 30% of carbon increased from the year 1850 to 1998, contributing more than 176 GtC in the atmosphere. The increasing trend has a strong relationship with the industrial revolution. Rapid industrialization (carbon emissions from those industries) and land-use change (deforestation, urbanization, agricultural practices) increase the carbon concentration in the atmosphere; in the meantime, they also destroy the significant carbon sinks in soil and forest. Now, the annual emission of carbon in the atmosphere is about 7.9 Gt. The net emission (more than 40 percent) from the terrestrial ecosystems is much higher than the absorption (slightly more than 30%).
The focus of the study
The carbon storage and release is a fundamental dynamic for living organisms and biodiversity, which is profoundly affected by climate change. This paper will focus on how climate change can change the carbon balance in global major carbon storages.
Scoping of the study
This writing considered only the temperature increasing component of climate change; so, mostly how global warming would destroy the present carbon sinks.
Background of the study
Changes of an ecosystem and land use planning change the capacity of carbon capturing and emission from the sinks. An ecosystem can be a sink or source, which depends mostly on the chemical and biological processes of that ecosystem. Those chemicals and biological processes are very temperature-dependent. Global warming is changing those processes and making ecosystems from carbon sinks into sources. The vulnerability of those ecosystems to carbon balance is a serious concern for future transformation and management perspectives to mitigate global warming.
Distribution of Global Carbon: 1. Land: Amount of carbon in Gt - 2100-2200, 2. Atmosphere: Amount of carbon in Gt - 720-800 and 3.Ocean: Amount of carbon in Gt - 38000-40000. Source: IPCC 1996:63.
Global warming is affecting the carbon sequestration and storage mechanism. Exploring how vulnerable we are to global warming led me to this investigation.
Soil carbon pool
Soil stores many times more carbon than plants. The soil organic carbon has a long residence time. Still, global warming could decrease the residence time by increasing microbial decomposition of soil organic matter, which will release more CO2 or CH4 into the atmosphere, which has a positive feedback loop to increase temperature again.
Carbon budget in soil depends on the balance between photosynthesis and respiration, specifically autotrophic root respiration and heterotrophic soil microbial respiration (RD Bardgett et al, 2008).
Soil vs Vegetation: 1. Soil: Amount of carbon in Gt - 951-1555 and 2. Vegetation: 262-880. Source: IGBP.
Soil respiration is sensitive to various factors including complex interactions and feedbacks between climate, plants, herbivores, symbionts and microbes (RD Bardgett et al, 2008). Even soil respiration is more temperature-sensitive than primary production (Schimel et al, 1994) Release of CO2 to the atmosphere and exports of dissolved organic carbon by hydrologic leaching will increase (RD Bardgett et al, 2008).
Warming could affect this process in two ways; firstly, the plants’ production, the diversity which alters soil physicochemical conditions, the supply of carbon to the soil. Secondly, the structure and activity of microbial communities involved in decomposition processes and carbon release to the atmosphere.
Carbon distribution in terrestrial ecosystem: 1. Agroecosystem: Amount of carbon in Gt - 263-487, 2. Grassland: Amount of carbon in Gt - 412-820, 3. Forests: Amount of carbon in Gt - 487-956 and 3.Other: Amount of carbon in Gt - 51-170. Source: IPCC 1996:639.
The issue becomes much more complicated when microbes are treated as important determinants of plant community diversity and productivity and the quality and quantity of carbon input to soil. (RD Bardgett et al, 2008)
Oceanic carbon pool
Due to global warming, the oceanic thermohaline circulation could be weakened or collapsed, which will reduce the uptake of carbon from the atmosphere excluded biological processes (Jorge L et al, 1996). As the stratification is temperature-dependent and due to global warming, more precipitation could occur in high latitude, which will decrease the salinity.
Warm water holds less dissolved gases. Due to warming, the holding capacity of carbon dioxide by marine water will also decrease. The biological cycle could compensate for this decrease by the downward mixing of carbon, except when thermohaline circulation collapses (Fortunat Joos et al, 1996).
The ocean can remove CO2 from the atmosphere, which is dependent on the atmospheric carbon dioxide pressure, mixing of oceanic water. These two are very much temperature-dependent. So global warming could reduce the carbon uptake at a significant level. Thus, atmospheric carbon will increase and give positive feedback to warming. These changing behaviours of the ocean could change the phytoplankton growth (significant sinks of carbon in marine water) as well as carbon storage capacity as biomass. If the ocean absorbs more carbon, then the pH will decrease which is very corrosive to the calcium carbonate shell which will ultimately affect the oceanic food web.
Temperature is a critical component of the climate which depends on many biotic and abiotic factors, and it has direct and indirect effects on biogeochemical cycles as well as ecosystem functioning. Global warming could trigger some feedback loops of carbon storage in a way which could imbalance the total ecosystem in such a way for which we are still not prepared.
Ashraful Haque is a system analyst. He started working as a research officer at ICCCAD in October 2018. He has earned several Masters, including in Environmental Sciences; Disaster Management; Sustainable Development. He also holds an MPhil in System Dynamics at the Universityof Bergen, Norway.