Concentrations of the main gases blamed for global warming reached record levels in 2010 and will linger in the atmosphere for decades even if the world stopped pumping out emissions today, according to the U.N.'s weather agency.

An ice age is a period when there is a long-term reduction in the earth's surface and atmospheric temperature, which leads to the growth of ice sheets and glaciers.

There have been at least five ice ages on earth. During ice ages there are cycles of glaciation with ice sheets both advancing and retreating.

Officially, the earth has been in an interglacial, or warmer period, for the last 10,000 to 15,000 years, and estimates vary on how long such periods last.

"(Analysis) suggests that the end of the current interglacial (period) would occur within the next 1,500 years, if atmospheric CO2 concentrations do not exceed (around) 240 parts per million by volume (ppmv)," the study said.

However, the current carbon dioxide concentration is of 390 ppmv, and at that level an increase in the volume of ice sheets would not be possible, it added.

The study based on variations in the earth's orbit and rock samples was conducted by academics at Cambridge University, University College London, the University of Florida and Norway's University of Bergen.

The causes of ice ages are not fully understood but concentrations of methane and carbon dioxide in the atmosphere, changes in the earth's orbit around the sun, and the movement of tectonic plates are all thought to contribute.

The world is forecast to grow hotter as greenhouse gases continue to rise, increasing threats such as extreme weather events and sea level rise.

Scientists have warned that global temperature rise should be limited to within 2 degrees Celsius to avoid the worst effects of climate change but delays in curbing emissions growth are putting the planet at risk.

(Editing by Alessandra Rizzo)

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