Today is Blog Action Day, an annual event where bloggers worldwide combine their energies to highlight a specific issue. Over 10,000 sites from more than 150 countries, are participating in this years discussion on climate change.

As part of EarthTrends contribution we will be highlighting a few key climate change trends and statistics.

Human influences have caused the levels of carbon dioxide in the atmosphere to rise dramatically over the course of the last 100 years. The concentration has increased from 299.2 parts per million by volume (ppmv) in 1909 to 385.34 ppmv in 2008, almost a 30% growth.

The chart above shows the top 10 historical emitters. Together these countries are responsible for more than 70% of the total cumulative carbon dioxide emissions in the atmosphere between 1900 and 2005. The United States alone is responsible for over 29% of the world total followed by the European Union (27) at 25% and China at 9%.

The question of historic emissions raises a number of equity and justice issues and has been a key point of contention at the UNFCCC negotiations. The world's developing nations, who have done least to add to historic emissions, want a treaty which focuses on these differentiated contributions. However a number of the industrialized nations argue that all countries share a common responsibility and should be making reductions.

China was the top emitter of greenhouse gases, contributing 18.72% of the world’s total followed closely by the United States at 18.33%. Things look very differently however when considered on a per capita basis which causes China’s ranking to drop from number 1 to 72!