“The MMCO [Middle Miocene Climate Optimum] was ushered in by CO2 levels jumping abruptly from around 400ppm to 500 ppm, with global temperatures warming by about 4°C and sea levels rising about 40m (130 feet) as the Antarctic ice sheet declined substantially and suddenly. ” — Skeptical Science
(Fossil fuel carbon emissions are about 100 times that of volcanoes during any given year. And so much heat trapping carbon dumped into the atmosphere is forcing the world’s climate to rapidly change. Image source: The Union of Concerned Scientists.)
Human beings have never seen atmospheric CO2 values that are so high as they are today. They significantly predate our species — even preceding our distant relative Australopithecus by about 7 million years. And weather and climate conditions to which we are not adapted — either as individuals or as a civilizations — are well on the way as atmospheric CO2 levels are ramping up into the lower range of those last seen during the Middle Miocene of 14-16 million years ago at 404 parts per million during 2016.
For the first 11 months of the year, 2016 atmospheric carbon dioxide concentrations exceeded those of 2015 by an average of 3.45 parts per million. With no sign evident that the pace of increase has slackened — despite a transition to La Nina during the fall — it now appears that the world is set to experience a 3.3 to 3.5 part per million jump in the atmospheric CO2 measure for this year.
(Atmospheric carbon dioxide concentrations will rise by a record rate during 2016 to an annual average of around 404 parts per million. Levels during 2017 could peak at around 410 to 411 parts per million in April and May before averaging between 406 and 407 parts per million. Image source: NOAA.)
All this fossil fuel burning has largely helped to push atmospheric CO2 values for 2016 into an average range of 404 parts per million. This is 124 parts per million higher than the pre-industrial value of 280 parts per million. Meanwhile, peak monthly values during April-May of 2017 could strike as high as 410 to 411 parts per million.
(15 million years ago, atmospheric CO2 levels in the range of 400-500 parts per million produced Antarctic melt resulting in substantial sea level rise. The above image shows the estimated location of the U.S. eastern coastline at the time. Image source: Colorado Geosystems.)
These atmospheric concentrations are now roughly equivalent to the lower range CO2 levels of the Middle Miocene climate epoch of 14-16 million years ago. Meanwhile, atmospheric CO2 equivalent concentrations, which include other greenhouse gasses like methane, averaged 485 parts per million in 2015 and likely were around 490 parts per million during 2016. These CO2e values approach the upper Middle Miocene range.
During the Miocene of 14-16 million years ago, atmospheric CO2 levels, which had hovered around 400 parts per million for about 10 million years jumped higher due to volcanic activity. Global temperatures rose from about 2-3 C hotter than Holocene values to around 4 C hotter. Antarctic ice melted and seas which were around 60 feet higher than today lifted to around 130 feet above present day levels.
By continuing to burn fossil fuels, this is the climate context we enter more and more. It is why, for example, we are seeing so many impacts from expanding droughts, to declining ocean health, to more extreme weather, to rapidly destabilizing glaciers in Antarctica. And it is this burning along with a related warming of the Earth System that is causing atmospheric carbon values to jump so rapidly into ranges to which we are unaccustomed.