Climate Change Impacts on Plant Biomass Growth

Plant biomass plays an important role in sustaining environment and life including human life on earth. The earth system is a closed system except for its absorption of solar energy. Green biomass is the only component of the earth system that captures bursts of solar energy, converts them, and allocates them to flows to other components and consumers of the ecosystem. In an ecosystem, where green biomass is the primary producer, humans occupy almost all positions, primary, secondary, or tertiary, within the consumer chain. Humans derive their essentials – food, fiber, fuel, and fodder – directly from green biomass and indirectly through other primary and secondary consumers of green plants. Hence, performance of green biomass growth in an ecosystem is not only important for smooth functioning of all components of the earth system but also for human existence in a befitting manner.

Climate change is a very well-discussed phenomenon. Still, we appear to be shocked when we hear about it. By climate change, we understand detrimental effects in environment – emission of pollutants, temperature rise, precipitation change, sea level rise, flooding, intensified cyclones, abrupt frequency of events, ozone layer depletion, biodiversity loss, vegetation change, and drought – almost all negative impacts. Indeed, climate change is an umbrella concept. Scientific evidence that humans were changing the climate first emerged in the international public arena in 1979 at the First World Climate Conference (WCC) (Depledge J, Lamb R. Caring for climate: a guide to the climate change convention and the Kyoto protocol. Climate Change Secretariat (UNFCCC), Bonn, Germany. 27 pp, 2005). Since then, it did not take long to reveal the dreadful consequences of climate change. By 1988, when IPCC was formed, the dangerous consequences of climate change became clearer.

In 1986, Swedish chemist Svante Arrhenius built the theoretical foundation of what has become known as the “greenhouse effect.” With remarkable prescience, he argued that if the carbon dioxide (CO₂) levels in the earth’s atmosphere were to increase to double the present average level, the average temperature could increase by around 4–6 degrees centigrade (°C) with critical implications for the earth’s climate (Falk JA, Brownlow A. The greenhouse challenge: what is to be done. Penguin Book, Ringwood, 1989). Indeed, industrialization and escalating global populations over the last two centuries have placed unprecedented pressure upon the natural cycle of the earth. Agricultural and industrial activities have given rise to changes in the chemistry of the lower atmosphere as a result of gaseous emissions in quantities beyond the capacity of the earth’s recycling systems. Certain gases in the atmosphere have a warming effect on the earth’s surface, due to their ability to absorb heat being radiated back out to space – “radiative forcing” as it is called by Reid (Research and technology opportunities for energy related reduction of greenhouse gas emissions in Australia. In Greenhouse and energy. In: Swaine DJ (ed) Greenhouse and energy. CSIRO, Canberra, pp 31–46, 1990). The irreversible effect of temperature increase due to this “radiative forcing” action of certain gases in the atmosphere is popularly known as the “greenhouse effect.”

The effect of climate change on vegetation is expected due to changes in the temperature, rainfall, and climate pattern as a result of which nutrient cycles, microbial activities, as well as physiological activities of plants will vary. Changes in precipitation may change moisture regimes. Soil erosion, salinity, acidity, and other physical and chemical factors may be affected as well. All these factors are closely related to vegetation growth. For example, with global temperature projected to rise to 3°C by the year 2030, this could cause the height of the sea level to rise by 0.8–1.8 m over the next century mainly due to thermal expansion of water and the melting of glaciers. A 1-m rise in sea level could jeopardize one-third of the world’s cropland either through direct flooding or through salt water intrusion and would enhance the emission of greenhouse gases further.

There are four principal reservoirs of regions of the earth through which carbon flows systematically: the atmosphere, the terrestrial biosphere, the oceans, and the geosphere, which include all forms of fossil. Carbon can be transferred between reservoirs and forms a network called the carbon cycle. The burning of fossil fuel, for example, currently generates an amount of CO₂ equivalent to 5 gigatons (10¹⁵ g = 1 Gt) of carbon annually. This carbon represents an additional transfer from the geosphere to the atmosphere relative to the balanced natural exchange of about 100 Gt C annually between the atmosphere and each of the remaining major carbon reservoirs resulting in a net increase of CO₂ concentration in the atmosphere (Blasing TJ. Background: carbon cycle, climate and vegetation response. In: White MR (ed) Characterization of information requirements for studies of CO₂ effects: water resources, agricultures, fisheries, forests and human health. United States Department of Energy, Washington, DC, 1985). Similarly, when a forest absorbs CO₂, deforestation, especially when the forest is burnt, adds considerable quantities of CO₂ to the atmosphere. CO₂ is also released when the forest vegetation decays and through the drowning forest. For example, a single dam, reservoir of the Balbina dam in the Brazilian Amazon, will yield as much CO₂ as would be produced by a coal-fired plant with a similar generating capacity operating for 100 years (Anon. Rainforest destruction: causes effects and false solutions. World Rainforest Movement, Malaysia, Jutaprint, 1991).

The area of the world’s managed forest is increasing at a rapid rate to meet the demand of a growing population with which natural forests cannot cope. An estimated increase of global population and the demand for wood is provided in Table 6.1 from which it is clear that managed forests are important in meeting the future demand of timber.

From the rotational curve presented in Fig. 6.3, we can understand that estimation of climate change impact may reveal different results on short-term and long-term bases. In practice, increase in the concentration of CO₂ is a slow process, and it may take a long period to predict any change in the biomass growth from the CO₂-induced effects. But both short- and long-term resolutions are important for management purposes. Positive management of climate change effect may be possible by looking at the reduction of greenhouse gas emission which can be a short-term as well as a long-term project or by improving the adaptability of green biomass through genetic manipulation which may be a long-term project. We are considering here the different aspects of short- and long-term resolution of climate change impacts on vegetation.

An attempt has been made in previous chapters to describe the impact of an increase in atmospheric CO₂ concentration on vegetation growth. The climate change effect is expected to bring some complex secondary changes in a series of environmental factors, and these changes may play a significant role in biomass production as well as in maintaining genetic diversity. Climatic change would influence biodiversity in two main ways:

There are arguments both for and against the effects of change in greenhouse gases on climate. If the assumption of a climatic effect is valid, the change in the regional climate may have some impact on the socioeconomic condition, and this may be particularly acute in some developing countries such as Bangladesh. The socioeconomic impact may also cover social health of the people. As there is some likelihood of a significant impact, strategic measures to prevent or control the greenhouse effect are becoming more important day by day. The importance of these strategic measures varies from society to society depending on their socioeconomic conditions. For example, given the dense population and poor social conditions in Bangladesh, there will be less awareness of the greenhouse effect than in Australia. The study of socioeconomic development is an important factor in strategic planning to combat the climatic impact of a single nation (several global organizations are already working on this issue). In order to improve the socioeconomic conditions of poor countries, a unified global action is needed so that the measures to combat the climate change effect do not appear as a hindrance to the development of such nations.

Climate change effects are complex phenomena involving water, soil, atmospheric gases, sunlight, and heat. An increase in the concentration of certain gases in the atmosphere causes the greenhouse effect. However, it has been established that there are sinks as well as sources for those gases in the atmosphere. The greenhouse gases may react with each other and with other gases in the atmosphere and partially nullify themselves. Scientists were divided on whether the greenhouse effect will actually happen or not, though on a short-term basis, it is certain that the concentration of different greenhouse gases in the atmosphere is increasing. This increase in greenhouse gas concentration could bring some changes in the growth of vegetation, and if the greenhouse effect develops and strengthens, climate change could bring about a drastic change in the growth and distribution of vegetation.