Scientists at the Beijing Normal University studied the link between climate factors and changes in plants' net primary productivity — a term used to evaluate the net reserve energy plants need during growth — between 1982 and 1999.

"If the net primary productivity of a plant is high, it means the plant grows more healthily," says lead author Zhu Wenquan of the College of Resources at the university.

Zhu and colleagues analyzed climate-observation data for the period alongside remote-sensing data on plantations in different regions in China. They then determined the specific climate factors — sunshine, temperature and precipitation — that had the biggest impact on plant growth in these regions.

They found that low temperatures in northeast China and the Tibet–Qinghai highlands contribute most to poor plant growth. In northwestern China it is reduced precipitation. And in southern and eastern China it is lack of sunshine that hinders growth.

But over the period studied, temperature, precipitation or sunshine increased markedly in these respective regions — effects that the scientists attribute to global warming.

"We are not denying the role of other factors, but the three factors (sunshine, temperature and precipitation) have played a much more important role than others," Zhu told SciDev.Net.

As a result, the net primary productivity of land plants in China grew by 11.5 per cent because of climate change, which the authors say is consistent with the global trend of an increase of about six per cent worldwide.

Zhu says this does not contradict the widely believed negative impacts of global warming. "For crops, for example, the growth in net primary productivity does not necessarily translate into increased output. The plant stem may grow more than fruits, for example."

He adds that climate change could cause severe disasters in individual regions, which would not be offset by increased plant productivity.

A previous study, published in 2004 by Gao Zhiqiang and colleagues from the Institute of Geographical Sciences and Nature Resources Research at the Chinese Academy of Sciences, concluded that climate change between 1978 and 1998 had caused a decrease in plant productivity in northeast China.

Referring to Zhu's studies, Gao says various aspects of climate change could combine to complicate the impact on plant growth, and it is difficult to associate a change in net primary productivity with variation of a single "major" climate factor.