In Terms of Life on Earth, Which Cycle Changes are More Significant: Water or Carbon? - Akshaya

Both the carbon and the hydrological cycle are vital to life on earth and are essential for the processes on the planet. Waterways support many species and thus increase biodiversity, as well as being an excellent store for carbon. Carbon is also necessary for life, as it is needed for photosynthesis. Both cycles interlink significantly and constantly affect each other.

Carbon is integral for life, and is formed as carbon based molecules in various forms; carbon dioxide and methane in the atmosphere, organic matter in the pedosphere, in carbon rich rocks, and in vegetation. Carbon is the basis of all life and is part of all the main molecules that form organisms (such as proteins, nucleotides, etc.), thus highlighting how carbon is necessary in all aspects of life on earth.

Water covers 69% of the world’s surface area, therefore it’s presence and the state of it greatly effects global systems. During colder periods of time, when much of the world is covered in ice such as during ice ages, there is a much greater albedo. This affects global temperature, as more sunlight is reflected away, creating a positive feedback loop and cooling the earth further. The opposite can also occur, where during warmer periods, such as the Medieval Warm Period, there is much less ice and therefore less albedo and the earth warms. Therefore, which sphere water is stored in (hydrosphere, cryosphere) greatly affects all life on earth. Both the cryosphere and hydrosphere are highly significant, as they both sequester carbon.

The importance of water storage on a smaller scale can be seen with the Exmoor Mires Project, where the aim is to restore the peat bog environment. Peat bogs are carbon sinks, and are short term stores of carbon. They increase water table height, which leads to more water retention and no decomposing micro fauna. Peat bogs can only exist and store carbon when water is present, as when dry, peat oxidises, which releases carbon; burning dry peat also releases carbon dioxide. Draining peat bogs can also lead to flash floods and erosion downstream. Peat bogs are highly important in reducing atmospheric carbon, and their presence is dependent upon water, once again highlighting the significance of the water cycle.

A predominant part of the fast water cycle is precipitation. Rainfall patterns are essential as they effect agriculture, business and life in an area. Climate change is causing rainfall patterns to alter, with some regions receiving more rain and others receiving much less than has been normal. Rainfall is vital for the biosphere, as rain is needed for photosynthesis (however, as is carbon). This is one of the most important processes for life on earth. Rainfall patterns are predicted to change as climate bands move away from tropical zones. This will lead to droughts in some areas and flash floods in others. Climate change is also likely to result in increased evaporation from oceans in tropical areas, with an increase in the intensity, extent and frequency of tropical storms causing severe damage to the natural and built environment where they are experienced.

Deforestation in the Amazon results in the feedback loop where more carbon dioxide results in higher temperatures, thus enhancing global warming. There is more carbon dioxide, due to the release of the stored carbon in the biosphere, and also by the process of slash and burn. This also sometimes leads to wildfires and further increases the carbon dioxide concentration, which is currently at 400ppm.

Water vapour is also a greenhouse gas; the impact of deforestation on the exchange of water vapour and carbon dioxide between the atmosphere and the terrestrial land surface hugely affects the climate system. Deforestation has decreased global vapour flows from land by 4%, and even a slight change in vapour flows can disrupt natural weather patterns and change current climate models. Therefore, the water cycle is also significant when discussing global warming. Sea level rise through thermal expansion of existing ocean volumes plus cryospheric water storage melts are forecast to lead to low lying coastal land being flooded, human crises, mass migration and environmental damage in the coming decades. Thus, showing the importance of water movements for humans and the environment.

Climate change greatly affects the water cycle, as the tropical Atlantic warms due to global warming, the large parts of the Amazon may see higher temperatures and less rainfall. These changes could dramatically affect the region’s ecosystem, by killing trees and leaving forests more vulnerable to fire. Many areas will experience longer periods of drought leading to environmental issues, such as soil erosion, fires, tropical disease extension and issues for food production. During the 2005 drought in the Amazon, many rivers dried up, remote communities were isolated, commerce slowed to a standstill. Droughts also affect the species composition of the forest, as some species, like fast-growing, light-wooded trees, are particularly vulnerable to reduced rainfall. Social and economic deterioration and mass migration also can occur as a result of drought. Thus, changes in the hydrological cycle have dramatic effects upon the earth.  

This 2005 drought had a huge effect on the carbon cycle, as thousands of kilometres squared of land burned for months, releasing over 100 million metric tonnes of carbon into the atmosphere. The drought and associated fires resulted in a net flux of 5 billion tonnes of carbon dioxide into the atmosphere, which is more than the combined annual emissions of Japan and Europe. Therefore, this is a positive feedback loop, where climate change affects the water cycle by evaporating waterways into the atmosphere, which results in an increase in carbon dioxide emissions, thus enhancing the greenhouse effect even more.

In conclusion, both cycles are hugely significant to life on earth, and we could not survive without the presence of both. It is difficult to evaluate which cycle is more meaningful, as they both interlink in countless ways and are constantly affecting one another. However, it does appear that the carbon cycle is slightly more important and has a greater effect, with carbon being part of all significant organic compounds. The carbon cycle also plays a greater part in climate change, which affects global processes considerably, and much of the water cycle’s importance is rooted in its ability to store carbon. Thus, the carbon cycle is fractionally more significant, but it is difficult to compare two cycles that are so tightly entwined.