(Annual mean CO2 growth rate for 2016 is likely to hit even higher than records seen during 2015 due to the influence of a record El Nino on the world ocean system’s ability to draw down excess atmospheric carbon and due to the fact that global CO2 emission remain near record high levels set in 2014. Image source:
NOAA ESRL.)
In 1998, during a then record El Nino and at a time when global carbon emissions from human sources were significantly lower than they are today and during a period when the global carbon stores appeared to be mostly dormant, atmospheric CO2 levels rose by a then record 2.9 parts per million. During 2015, as a record El Nino ramped up and as the global carbon stores continued their ominous rumbling, annual average increases hit a new high of 3.05 parts per million. But with the strongest El Nino impacts hampering ocean carbon draw-down extending on into the current year, it appears that 2016 average rates of atmospheric CO2 increase are likely to be even higher. Due to this, hopefully temporary, reduction in the ocean’s ability to take in atmospheric carbon, we’re likely to see May 2016 CO2 levels at Mauna Loa hit a range of 3.1 to 5.1 parts per million (407 to 409 ppm in total) above previous record high levels of around 403.9 parts per million for the same month during 2015.
The Last Time CO2 Values Were So High Was During the Middle Miocene — 15 Million Years in the Earth’s Deep Past
By any yardstick, these are extreme annual rates of atmospheric CO2 increase.
Rates that are likely at least an order of magnitude faster than during the last hothouse extinction — the PETM — 55 million years ago. Just a few years ago, the scientific bodies of the world voiced serious concern about atmospheric CO2 levels equaling those seen during the Pliocene period — a geological epoch 3-5 million years ago when Earth temperatures were 2-3 C warmer than they are today and atmospheric CO2 levels ranged between 390 and 405 parts per million. But in just a brief interval, we’ve blown past that potential paleoclimate context and into another, more difficult, much warmer, world. A period further back into the great long ago when human civilization as it is today couldn’t have been imagined and a species called homo sapiens had millions of years yet to even begin to exist.