Earth is protecting humanity from the full effects of global warming by soaking up increasing amounts of carbon, research has shown.
Once the forests and oceans become saturated, as scientists predict, the impact of greenhouse gas emissions is expected to double. But no-one yet knows when this time will come.
Researchers in the United States studied global carbon dioxide (CO2) emissions over the past 50 years and compared them with rising levels of the gas in the atmosphere.
They found that while CO2 emissions had quadrupled in the last five decades, natural carbon "sinks" that capture the greenhouse gas doubled their uptake. This had lessened the impact of man-made CO2 emissions on the Earth's climate.
"What we are seeing is that the Earth continues to do the heavy lifting by taking up huge amounts of carbon dioxide, even while humans have done very little to reduce carbon emissions," said lead researcher Dr Ashley Ballantyne, from the University of Colorado at Boulder (CU-Boulder). "How long this will continue, we don't know."
A total of 33.6 billion tons of CO2 were emitted globally in 2010, climbing to 34.8 billion tons in 2011, according to the International Energy Agency.
Much of this carbon is absorbed by the oceans and soil, or captured by green plants.
Plants absorb around 66 billion tons of carbon from the atmosphere each year to generate energy and renew themselves.
Oceans absorb about a third of man-made CO2 emissions, roughly 22 million tons a day.
The new findings were published in the journal Nature.