The Kyoto Protocol invented the concept of carbon emissions trading in a flexible mech­anism whereby developed countries could use carbon credits to meet their emission reduc­tion commitments. The world carbon market is based on a cap-and-trade system. According to Mark Lazarowicz (2009), under cap-and-trade, a cap is set on emissions, as explained fur­ther by the author: "Allowances are provided, either through purchase or allocation, to emit­ters covered by the cap. These emitters are required to submit allowances equal to the amount of greenhouse gases emitted over a predetermined period. The difference between expected emissions and the cap creates a price for the allowances. Emitters who can reduce emissions for less than the price of an allowance will do so. If, however, abatement costs more than the price of an allowance, it makes sense to purchase the allowance. The transfer of allowances is the ‘trade.’ The relative difficulty of abatement or scarcity of allowances sets the price of carbon. In theory, those that can reduce emissions most cheaply will do so, achieving the reduction at the lowest possible cost." For this reason, the carbon market seems to be a tem­porary alternative while cleaner technologies are developed, including new ones and improvement of the existing ones.

The carbon market jumped from $63 billion in 2007 to $126 billion in 2008, which means almost 12 times the value of 2005, according to the World Bank report of 2009. Credits were sold for 4.8 billion tons of carbon dioxide, a value 61% higher than that of the previous year. By 2020 the market could be worth up to $2-3 trillion per year (Point Carbon, Carbon Market Transactions in 2020: Dominated by Financials?, May 2008).

The world carbon market is mainly dependent on energy-use policies. The focus is to replace existing high dependence on fossil fuels with renewable ones; around 90% of total global CO2 emissions are from fossil fuel combustion (excluding forest fires and woodfuel use; Olivier et al., 2011). The principal technical means of reducing fossil fuel consumption (and conse­quently emissions) are substituting fossil fuels with renewable or less carbon-content sources of energy and improving energy efficiency. Renewable energy’s share of the global energy supply increased from 7% in 2004 to over 8% by 2009 and 2010 (Olivier et al., 2011).

According to the "Long-term trend in global CO2 emission, 2011 report," total global CO2 emissions had increased 30% since 2000, to 33 billion tones, and 45% since 1990, the base year of the Kyoto Protocol. In 1990 the industrialized countries, with a mitigation target for total greenhouse gas emissions under the Kyoto Protocol (including the United States, which did not ratify the protocol), had a share in global CO2 emissions of 68% versus 29% for developing countries. In 2010 the large regional variation in emission growth trends resulted in shares for 54% of developing countries and 43% for mature industrialized countries.

Microalgae can play a very interesting role in this context. While fixating carbon during growth (to be traded in the market), some species can accumulate lipids, which can be use for direct combustion or transformed in biodiesel to replace fossil sources. This is one of the developing technologies that receives more attention from the scientific community around the world.

The carbon market for microalgal carbon mitigation processes is a big challenge. Its en­trance in this market will coexist with other renewable energy technologies that are receiving lots of investment, which means that it must be more advantageous or differentiated. Trades of carbon papers are carried mainly based on agriculture and forestry (reforestation, land management, reduced emissions from deforestation). Great efforts are being made in the de­velopment and implantation of renewable energy technologies (wind power, solar photovol­taic, and vegetable-based biodiesel technologies).

In terms of development of more efficient and sustainable industrial processes, microalgae can play an interesting role through combining the use of domestic and industrial wastewater (mainly that lacking fermentable carbon) and industrial gaseous wastes with cogeneration of valuable products, reducing carbon emissions and generating tradable carbon papers. According to the mass balance (Equation 4.3), where the biomass composition is given as CH178 No.15Oo.52 (analysis made in CHNS analyzer carried at the Bioprocess Engineering and Biotechnology Department, Federal University of Parana, Brazil), around 1.8 gCO2 is con­sumed for each gram of dry biomass produced during microalgal growth. This means that, for producing 1 Carbon Paper (1 ton CO2), an area less than 1,000 square meters is needed (considering a biomass concentration in the culture of 3 g L-1 and a pond with 20 cm high of liquid).

0. 815 H2O + CO2 + 0.15 HNO3 ! CH1.78 N0.15O0.52 + 1.37 O2 (4.3)