Many scientists are certain that as the figure rises Mankind is edging closer to triggering runaway climate change, a catastrophe that could last hundreds of years and our descendants would be powerless to stop.
So no wonder the slogan we see for the World Environment Day 2008 on June 5 is: Kick the habit! Towards a low carbon economy.
Building a low-carbon economy has become one of the central challenges of our age. It will require the restructuring of the global energy industry through unprecedented technological, economic and policy innovations.
According to the report "State of the World 2008 - Innovations for a Sustainable Economy" released by the World watch Institute earlier this year, the first step in establishing the viability of a climate-safe energy strategy is assessing the available resources and the potential role they might play.
Several reports show that resource availability will not be a limiting factor for the efforts to replace fossil fuels.
A global assessment by the McKinsey Global Institute shows that the greatest potential is in buildings, the most basic element of the energy economy, which could be improved with better insulation, more-efficient lighting and better appliances.
On the supply side, one of the low-carbon energy sources receiving much attention these days is nuclear power, which already plays a major role in some countries. Taken as a largely carbon-free energy source that could in theory help phase out fossil fuels, more than 300 nuclear plants currently provide 15 percent of the world's electricity.
Several studies have assessed the scale of the major renewable resources and their practical contribution to the low-carbon economy in the future. A study by the U.S. national Renewable Energy Laboratory shows that solar thermal power plants built in seven southwest U.S. states could provide nearly seven times the country's existing electric capacity from all sources.
The U.S. Pacific Northwest Laboratory found that the land-based wind resources of Kansas, North Dakota and Texas could meet all the electricity needs of the U.S.
To seriously de-carbonize the current energy economy, the greatest challenge perhaps lies in how to integrate the new energy resources into the existing energy infrastructure that was designed around fossil fuels.
Electricity is the most important element of today's energy system. Mostly produced by coal-fired power plants, it also happens to be the largest and most easily replaced contributor to carbon emissions because almost all renewable sources, including solar, wind, geothermal, ocean and bioenergy, are all able to produce electricity.
After reliance on coal is reduced in the decades ahead, the World Watch Institute recommends a combination of three strategies: add local generating capacity using micro turbines and fuel cells; move to digital "smart" grids that are more flexible in their ability to balance demand and supply; and develop the capacity to store energy economically.
A "smart" power grid could respond in real time to decisions made by users. For instance, it could lower the electricity supply when the customer is not at home, and it could also allow unneeded devices to be turned off when electricity prices are high or renewable resources are not available.
The new generation of micro-power generators, such as fuel cells, could further aid the "smart" electricity grids. In Japan, many families are generating electricity with solar cells which send power to the local grids and draw from them at the same time.
Another challenge in tackling climate change lies in the policy decisions made at international, national and local levels.
According to many energy economists, the relative lower cost of fossil fuels compared with the alternatives is the reason why they dominate energy consumption today. Therefore, putting a price on carbon emissions, such as a tax or a cap looks like a good idea to tackle climate change.
However, the large difference of the carbon price label demonstrates much more is needed to be done. In Europe, the current price of a carbon credit is about 32 dollars (US) per ton, while the U.S. caps the price of carbon at only 12 dollars.
Consumers are also facing many obstacles while planning to make investments in energy efficiency, spurring a requirement for more government mandates. For instance, many countries require home appliances, motor vehicles and buildings to meet some efficiency standards in order to be sold.
The policy-makers around the world also need to think about how to make the energy markets reward innovation and investment that strives to achieve the best possible performance.
As people around the world have come to understand that a low-carbon economy could be more effective than today's form, the political agreements on climate change are advancing more rapidly compared with the paralysis situation several years ago, however, the world is yet to reach a point where it can ensure an economic transition to a low-carbon society.