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Plants are slowing the effects of climate change far more than expected, researchers have found.

They said the impact of rising CO2 levels on plant growth has been underestimated by 16 per cent, as they thrive with more CO2 in the atmosphere.

And as plants absorb CO2, this has led to overestimates of how much of the greenhouse gas is left in the atmosphere.

Researchers say the impact of rising CO2 levels on plant growth has been underestimated by 16 per cent.

The study was conducted by climate and earth scientists at the University of Texas at Austin and Oak Ridge National Laboratory in Tennessee.

It says a 16 per cent 'correction' would be 'large enough to explain the persistent overestimation of growth rates of historical atmospheric CO2 by earth system models'.

'Our study will lead to improved understanding and modelling of carbon–climate feedbacks,' the paper says.

Lianhong Gu, from the Climate Change Institute at Oak Ridge National Laboratory in the United States, said most carbon-cycle models had over-predicted the growth rate.

Dr Gu said the growth rate of carbon levels had been over-predicted by 17 per cent over a 100-year period.

The study in the Proceedings of the National Academy of Sciences focusses on the slow diffusion of CO2 in plant leaves, with particular attention to the mesophyll or their inner tissue.

It concludes: 'Carbon cycle models that lack explicit understanding of mesophyll diffusion will underestimate historical and future terrestrial carbon uptake.

'Consequently, they will overestimate historical and future growth rates of atmospheric CO2 concentration due to fossil fuel emissions, with ramifications for predicted climate change.' 

Professor  Peter Cox, Professor of Climate System Dynamics at the University of Exeter, said even if the study was correct, the effect will be 'relatively small' compared to uncertainties about how much carbon will be absorbed by plants and soil.

Researchers said the growth rate of carbon levels had been over-predicted by 17 per cent over a 100-year period.

He said: 'Avoiding 2C of global warming is a huge challenge for humanity even if this effect is taken into account.' 

Prof Richard Betts, Head of Climate Impacts Research at the Met Office and Chair in Climate Impacts at the University of Exeter, said:

'This is a very interesting paper adding to our understanding of plant physiology. 

'The authors remark on the potential importance of their results for global carbon cycle modelling, and this is indeed relevant, but as a priority for improving carbon cycle modelling there are other processes which current models treat either very simplistically or not at all. 

'Fire disturbance, for example, is not included in some of the models examined here – its inclusion could be more important than any improvements in modelling CO2 fertilization, as it seems likely to be an important feedback on climate change. 

'Changes in global soil respiration at the global scale are also poorly understood.

'So while this is an interesting and useful contribution, it should be put into context with the bigger picture – disturbance mechanisms as well as physiological processes are important.'

In a separate study, reported in the same journal, scientists artificially elevated CO2 levels in a US prairie grasslands ecosystem for eight years. 

They found that the added carbon had increased the overall volume of the plants and promoted the ecosystem's stability by reducing the growth of normally dominant plant species.