阅读理解 The ability of forests to absorb man-made CO2 is weakening, according to an

阅读理解

The ability of forests to absorb man-made CO₂ is weakening, according to an analysis of two decades of data from more than 30 sites in the frozen north．

The study was conducted by a team of Canadian, Chinese and European researchers and published in the science journal Nature on January 3．The findings mean that more of the CO₂ we release will end up affecting the climate rather than being safely locked away in trees or soil．

As plants take up more CO₂, that should put a break on CO₂ increases, scientists once thought．However, the new data suggest that this idea is too simplified．The research team monitored the date in autumn at which the forests switched from being a net sink for carbon into a net source．Instead of moving later in the year as they had expected, this date actually got earlier－in some places by a few days, but in others by a few weeks．

“This means potentially a bigger warming effect,”said Timo Vesalai, who led the study．The precise effect the trend will have on future warming is hard to predict．But the research could partly explain why the amount of CO₂ in the atmosphere is increasing faster than expected．

Currently, half of the man-made CO₂ is absorbed by oceans and ecosystems on land．

Between 1970 and 2000, the CO₂ concentration(浓度)in the atmosphere rose by 1.5ppm．Since 2000 the annual rise leap to an average of 1.9ppm－35％ higher than expected．

In China, the average temperature in 2007 was 1.3℃ higher than the average temperature between 1970 and 2000．

So, it is time for us to take action now．

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