FACTBOX - How scientists are trying solve the carbon riddle

REUTERS - For decades, scientists have been measuring carbon dioxide and other greenhouse gases to gauge annual increases as well as to better understand how mankind is changing the world's atmosphere.

But scientists have struggled to build an accurate picture of how the gas is continuously shifted around by the atmosphere or precisely how much is soaked up by oceans and plants or emitted by rotting and burning vegetation and other natural processes.

Add to the mix mankind's carbon dioxide emissions from burning fossil fuels, deforestation and agriculture. This complex picture makes independently monitoring a specific region's natural take up of CO2 or a country's carbon emissions currently impossible on a near-real time basis.

HOW MUCH CARBON DOES MANKIND ADD?

The amount of CO2 that moves in and out of natural sources and sinks in the global carbon cycle is much greater than the emissions from mankind's emissions from industry, transport and agriculture. But every year, more and more of mankind's emissions stay in the atmosphere, with plants and oceans unable to absorb all the extra gases.

Mankind's CO2 emissions total about 30 billion tonnes per year. Of this, about half stays in the atmosphere, while about 7.5 billion tonnes is taken up by the oceans and roughly the same amount by land plants.

But exactly how much is taken up by specific regions, such as the Amazon rainforest, remain unclear.

Since 1750, the start of the Industrial Revolution, mankind's emissions have caused the concentration of CO2 in the air to increase by about 100 parts per million (ppm) to nearly 390 ppm. It took until the 1970s to reach the first 50 ppm increase. The next 50ppm increase occurred in the following 30 years, according to the U.N. Climate Panel.