According to Pieter Tans, the doyen of the field at NOAA, the country currently has 17 or 18, so that will improve things by a factor of four.

据NOAA的元老级人物彼得。坦斯称，美国目前为止有17,18台，所以增加的监测器可增加到原来的4倍。

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The last time the worldwide carbon level probably hit 400 ppm was about 2 million years ago, said Pieter Tans of the National Oceanic and Atmospheric Administration.

NPR: Experts: CO2 Record Illustrates 'Scary' Trend

The last time the worldwide carbon level was probably that high was about 2 million years ago, said Pieter Tans of the National Oceanic and Atmospheric Administration.

NPR: Greenhouse Gas Milestone; CO2 Levels Set Record