A number of complex connected physical, chemical and biological processes occurring in the atmosphere, land and ocean determine global climate. The biophysical state of the Earth's surface and the atmospheric abundance of a variety of trace constituents affect the radiative properties of the atmosphere (IPCC, 2007). Such constituents include carbon dioxide (CO2) as well as other active constituents. Processes such as natural and human emissions of gases, transport at a variety of scales, microphysical transformations and chemical, surface uptake by the land and terrestrial ecosystems, and the ocean and its ecosystems determine the composition of the atmosphere (Sarmiento and Grubal, 2006). The rates of biogeochemical cycling processes, are influenced by climate change, and involve interactions in and between the components of the Earth system. These interactions produce negative or positive feedbacks and are generally nonlinear to the climate system.
Past climate evolution studies can explain mechanisms that could generate nonlinear responses to external forcing on different time scale. Specifically, this essay will examine the relationships between the physical climate system and land surface, carbon cycle, concentrations and causes of carbon dioxide, seasonal and latitudinal variation, changes with time, and the effects of carbon dioxide.
Surface climate interacts with biomes, and fire, soil and respiration of vegetation, all of which are important for the carbon cycle. Various processes in terrestrial ecosystems affect the flux of carbon between atmosphere and the land. As temperature, CO2, and precipitation increases, terrestrial ecosystem photosynthetic productivity changes in response. When climate becomes more positive for growth, carbon uptake from the atmosphere is improved (IPCC, 2000).
Carbon dioxide plays a crucial role in a multifaceted global cycle. It is emitted from the interior of the earth and produced by respiration of soil microbia, fuel combustion and oceanic evaporation (Bolin et al, 1979).However, carbon dioxide (CO2) is dissolved and consumed by plant photosynthesis in the oceans. The imbalance between absorption by the oceans, terrestrial biosphere and emission leads to the net atmospheric increase. The exchange between various Earth systems elements and the carbon reservoirs are illustrated by the carbon cycle. Figure.1
Figure 1.Global carbon flow in gigatonnes: 1Gt= 1012kg plus gross annual fluxes (IPCC, 1990 and 2001)
This figure indicates a present comprehension of the system as a general ocean-atmosphere-terrestrial system with quite strong ocean-atmosphere and earth-atmosphere connection and quite weak earth-ocean interchanges. Natural systems, earth-atmosphere and ocean-atmosphere exchanges dominate the gross fluxes within the carbon cycle (Wuebbles and Edmonds, 1991; IPCC, 2007; Bolin, 1986).
Seasonal, Latitude and Time Variations
In 2007, carbon dioxide contents of the air, with a mean of 387ppm has a significant seasonal range in higher latitudes in the Northern Hemisphere coupled with decay and photosynthesis in the biosphere(Barry and Chorley,2010).The mixing ratio ranges from 380ppm in Autumn to 393ppm in spring.
The amount of CO2 and other gas particles in the atmosphere undergo long term change, which play a crucial role in the earth's radiation budget. Since, 1750 the beginning of the industrial period, measurements has shown an increase in trace of all atmospheric gases (Karol, 2004) (Table.1).
Table 1.Human induced changes in concentration of atmospheric trace gases
Annual increase(%) 1990s
Rise paddle, cows
Houghton et al, (1996)
Oxidation of fossil fuel is the primary source of these increasing concentrations. Energy of 5*1020J/y is generated by both transportation, and industrial activities. Thus, natural gas and oil consumption are responsible for 60 percent of global energy and coal account for 25 percent (IPCC, 1992). Combustion of coal and oil releases not only CO2 but also nitrogen. The atmospheric composition can be modified by other factors related to land use change, such as land clearance (Schimel et al, 1996).
Concentration and Sources
The atmospheric concentration of carbon dioxide (CO2) mixing ratio has been stable preceding 1750, between 260-280ppm (IPCC, 2007).Perturbation by anthropogenic activities on the carbon cycle were insignificantly relative to natural variability. Since 1750, annual global atmospheric burden of CO2 concentration has risen. The major reservoirs of carbon are in sediments and fossil fuel. 800*1012kg of carbon, equivalent to a CO2 concentration of 387ppm is contained in the atmosphere (Bolin, 2001). The crucial fluxes of carbon dioxide are a result of photosynthesis, respiration, and dissolution in the ocean. Carbon dioxide average time it takes to be dissolved in the ocean is 4 years. Primary production on land from photosynthetic activity involves 50*1012 kg of carbon/y (Wisniewski and Lugo; IPCC, 2007).
Human activities have resulted in increased atmospheric CO2,such as land-use change, biomass burning, and primarily emission of carbon from stocks of natural carbon through the oxidation of fossil fuel and cement manufacture, but also deforestation(IPCC,2007).Current global rates of emission from fossil fuel combustion are approximately 6PgC/y (IPCC,1992;Marland,et al 2006).Existing rates of emission from tropical deforestation, are estimated to be 1.6±1.0PgC/yr(IPPC,1992;Wisniewski and Lugo,1992).
Rates of fossil fuel emission in the 19th century were small relative to present rates, and relative to estimated rates of carbon release from land use change. Emissions from fossil fuel carbon have grown from 0.1 PgC/y in 1860(Boden et al., 1990). Pre-industrial concentrations have been estimated using ice core measurements that indicate that the concentration in 1800 was 280ppm (IPCC, 1990), figure 2.
Figure 2: Atmospheric CO2 concentrations estimates: since 1800 from air bubbles in Antarctic ice core and projected trends for this century (NOAA, 2012).
As regards to change in land use, the basic issue is that increasing population pressures have lead to deforestation acting to increase the earth's surface albedo (Barry and Chorley, 2010).Even as radiative forcing relative to 1750 is a modest-0.2Wm-2, anthropogenic impacts on vegetation cover have a history. Aborigines in Australia have a history of burning vegetation which has been traced over the last 50000years ago, whilst deforestation began during Neolithic times 5000years ago in Eurasia (Sioli, 1985).Deforestation and biomass combustion has contributed about 2*1012kg C/y concentrations. Forest is a sink of carbon, and left alone buffers the carbon dioxide in the atmosphere. Biomass burning is projected to account for 25 percent of the increase in atmospheric carbon dioxide since pre-industrial era (Barry and Chorley, 2010).
The oceans play a crucial role in the global cycle. Carbon dioxide is exchanged between the ocean and the atmosphere. Carbon dioxide as it enters ocean surface reacts with water to form carbonate (CO32-) and bicarbonate (HCO3-) ions. The residence time of carbon dioxide in ocean, comparative to exchange with the atmosphere and physical exchange with the ocean is less than 10 years (Sarmiento and Gruber, 2006).From 1750 and 2008 atmospheric carbon dioxide mixing ratio have increased by 38 percent, from 280 to a highest value for 650,000years of 387ppm (Barry and Chorley, 2010) (Figure 3).Since the mid 1960s, atmospheric CO2 levels are increasing by 1.5-2ppm/y. The main net source is fossil fuel combustion, now responsible for 6.55*1012kg C/y.
Variation in carbon dioxide concentration during the past 400,000 years (historical data from the Vostock ice core).
Figure 3; illustrate evidence contained in ice core samples that atmospheric CO2 has increases since the industrial revolution era (NOAA, 2012)
The Impact of Carbon dioxide (CO2)
The continuous amplification in carbon dioxide, since the last century, has resulted in a changed atmospheric environment for the world's vegetation cover. Hence it appears necessary to consider changes in carbon dioxide enriched environment of vegetation dynamics that occur at the landscape level.
Few coupled climate carbon model demonstrate the possibility of large feedback between future climate and vegetation change(Betts et al,2004).They also indicate that the physiological forcing of stomatal closure by rising atmospheric carbon dioxide concentrations could contribute 20 percent to rainfall reduction (Sioli, 1985).
Carbon dioxide absorption of radiation from the ocean and atmosphere has a major impact on global temperature. Calculations show increase in the 1960s of 320ppm to 387ppm in 2008, increased the mean surface air temperature by 0.6oC.Since 2000, the rate of increase in carbon dioxide is 2ppm/y compared with less than 1ppm,1.5ppm in the 1960s and 1980s(Barry and Chorley, 2010).
Evidence from paleo-climate indicate that surface warming at high latitudes will be 2-5 times the global mean warming (IPCC,2007).The model predicts high latitudes sensitivity and trace it to ice-snow albedo feedback, and greater atmospheric stability, which magnifies warming of near-surface layer(Diaz and Kiladis,1995).
Global warming cannot be expected to result in a uniform temperature increase. Regional differences can be predicted by general climate circulation model. For instance, the upswing of global average temperature from 1975 to 1987 coincided with 2 major El Nino southern oscillation events in 1982-83 and 1986-87(Henderson-Sellers, 1990).Increased storms and more frequent weather disturbances under increased carbon dioxide (CO2) condition and accelerated forest dieback was predicted by Overpack et al., (1990).
To concludes, human activities are responsible for the major increase in carbon dioxide among the Earth system components. Carbon dioxide change with time and has long residence time in the atmosphere. It affects the global climate system through climate feedback and responses to rising temperature leading to global warming resulting in extreme weather pattern and melting of ice-snow.