In the past 20 million years the atmospheric CO2 level seems to have never exceeded 300 parts per million (ppm), fluctuating between 180 ppm during glacial periods and 280 ppm during interglacial periods (Rost and Riebesell, 2004). Atmospheric CO2 values before the industrial revolution were also 280ppm. Today´s measurements from the NOAA are 396.8 ppm. By the year 2100 they are projected to range from 660 to 790 ppm, (IPCC, 2007).
As mentioned in the brief explanation of major changes in the carbonate chemistry, under more acidic conditions, the equilibrium of the carbonate system – which encompasses all the carbonate forms into which CO2 dissociates in water- will go towards higher HCO3– and CO2 while CO3– concentrations and pH level will go down. The last two are expected to decrease by about 50% by the end of our century.
The IPCC (Intergovernmental Panel on Climate Change) has released the different scenarios for future atmospheric CO2 conditions. Many works in biogeochemistry have used the IS92 series of scenarios published in 1992. But most present scenarios are reports in the SRES published by IPCC. The following figure (taken from Raupach et al., 2007) shows the observed emissions (black lines) by two investigation centers (CDIAC and EIA) compared with IPCC scenarios. Two of these scenarios were stabilization of the CO2 emissions are reached at 450 and 650ppm. The 6 others (A and B) are from the IPCC scenarios. As you can see, in the last years considered in the curve, the observed emissions were in the upper edge (worst) of the IPCC scenarios and, unfortunately, it even exceeds the predictions.
And extending the time scale….
The A scenarios are characterized by economic globalization while the B scenarios assume assume regional economic development. The number ‘1’ behind each A and B scenarios focus on an economically-oriented development and the ‘2’ scenarios emphasizes on an environmentally responsible management of resources. Within the A1 scenarios, A1F1 considers intensive dependence on fossil fuels, in A1T alternative technologies largely replace fossil fuels and in A1B there is a balance between fossil fuels and alternative energy technologies.
Although several uncertainties make it difficult to evaluate exactly how much atmospheric CO2 there will be in the atmosphere and in the ocean of our planet, one thing is for sure: it has already increased a lot and at unprecedented rates. In the last 55 million years, we humans have never experienced this before. Not to mention major changes in ocean carbonate chemistry that are coming along with it ! How will the oceans respond? That is why we are in Villefranche now!