We're currently at 390 ppm and projected to hit 650 ppm by the end of this century.

但现在我们这一数字已经达到百万分之390, 而且预计到本世纪末会达到百万分之650。

After 400 ppm, who knows what will happen?

400/100 万之后，谁知道会发生什么？

A rock from the region was found to carry 180 ppm of water, much drier than those found on Earth.

该地区的一块岩石被发现携带 180 ppm 的水，比地球上发现的要干燥得多。

For example, a concentration of just 35 ppm of carbon monoxide in the air is poisonous to us.

例如，空气中浓度仅为 35 ppm 的一氧化碳对我们来说是有毒的。

The last part of the inscription was 415 ppm CO2, the record level of carbon dioxide in the atmosphere that was recorded in May.

铭文的最后一部分是“415ppm的二氧化碳”，这是5月份记录的大气中二氧化碳的最高水平。

AT NOON on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm).

5月4号中午，夏威夷莫纳罗亚观测站测量到其附近大气层中，二氧化碳的浓度达到400ppm。

This is a big change from a hundred years ago when the concentration was just 300 ppm, below which it had stayed for more than 800,000 years.

相较于 100 年前，这是巨大的变化（那时的浓度只有 300/100万，保持了 80 万年之久）。

In some respects, 400 ppm is just an arbitrary figure, an attractively round number like the four-minute mile or the 7 billion mark for world population, but it indicates that we have reached a new phase of our experiment.

从某些方面考量，400/100 万只是一个武断的数字，一个吸人眼球的大致数字，就像四分钟一英里，或世界人口 70 亿标志一样，但它可以表明：人类的实验到达了一个新的阶段。