(a,b) Proxy-based atmospheric CO2 on a log timescale with best fit LOESS and associated uncertainty envelope. (c) Ice core atmospheric CO2 from ref. 82 on log timescale. (d) Atmospheric CO2 on line timescale from ice core and observation record82 and future RCP8 and other41 scenarios (RCP3PD—grey, RCP4.5—orange, RCP6—red, RCP8.5—brown, Wink12k -black)38,40. (e–h) ΔFCO2,sol calculated from data shown in a–d as described in text. In (c) ΔFCO2,sol is calculated from ice core CO2 estimates assuming no change in solar output82. No change in solar output is also applied to the records in h. Graphic: Foster, et al., 2017 / Nature Communications

By Chelsea Harvey
5 April 2017 WASHINGTON (The Washington Post) – Continuing to burn fossil fuels at the current rate could bring atmospheric carbon dioxide to its highest concentration in 50 million years, jumping from about 400 parts per million now to more than 900 parts per million by the end of this century, a new study warns. And if greenhouse gas emissions continue unabated beyond that point, the climate could reach a warming state that hasn’t been seen in the past 420 million years. Some research suggests that, if humans burned through all fossil fuels on Earth, atmospheric carbon dioxide concentrations could hit 5,000 parts per million by the year 2400. The new study speaks to the power of human influence over the climate. It suggests that after millions of years of relative stability in the absence of human activity, just a few hundred years of anthropogenic greenhouse gas emissions are on track to cause unprecedented warming. To come to these grim conclusions, which were published Tuesday in the journal Nature Communications, the researchers constructed a continuous record of atmospheric carbon dioxide concentrations spanning the last 420 million years. They created the record by compiling more than 1,500 estimates of atmospheric carbon dioxide concentrations drawn from 112 published studies. [more]

Carbon dioxide levels could reach their highest point in 50 million years by the end of the century

ABSTRACT: The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm−2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm−2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.

Future climate forcing potentially without precedent in the last 420 million years