There's a saying that trouble comes in threes. Earlier this week, the International Energy Administration announced that emissions reached a record high last year, increasing by 1 Gt worldwide. At the Bonn climate talks, experts have warned that the window to curb a global temperature rise of more than 2 degrees is swiftly drawing to a close.

To cap it off, NOAA released the news that carbon dioxide levels have reached a new milestone this spring, tipping the scales over 400 ppm, a concentration the world hasn't seen in the last 800,000 years.

Scientists are seeing these high concentrations at their northernmost stations in the Arctic. Remote sites measure the gas in Alaska, Canada, Iceland, Finland, Norway, and also an island in the North Pacific, Mauna Loa, which has been recording ambient CO₂ concentrations since 1959 (and produced the now-famous Keeling curve).

The global average is still around 395 ppm, but the Arctic is seen as an important indicator for global conditions to come, since it is an ecosystem that is much more sensitive to changing conditions.

“The northern sites in our monitoring network tell us what is coming soon to the globe as a whole,” said Pieter Tans, an atmospheric scientist with NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colo. “We will likely see global average CO₂ concentrations reach 400 ppm about 2016.”