Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison

Abstract

Eleven coupled climate-carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO 2 for the 1850-2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO 2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO 2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO 2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO 2 levels led to an additional climate warming ranging between 0.1°and 1.5°C.All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.

High Resolution Fossil Fuel Combustion CO2 Emission Fluxes for the United States

“…Because of the reliability of direct CO 2 monitoring and the need for fine time resolution data, we utilize CO 2 Nonroad emissions are structured similarly to the onroad mobile emissions data and consist of mobile sources that do not travel on designated roadways. These data, retrieved from the NMIM NCD, have a space/time resolution of county/month and are reported as activity (number of hour/month vehicle runs), population and a CO 2 emission factor specific to vehicle class (27,32).…”

“…Recent research has highlighted the importance of feedbacks between climate change and carbon uptake in the oceans and land, emphasizing the considerable spread in projected atmospheric CO 2 concentration due to uncertainties in surface-atmosphere exchange (2). The single largest net flux of carbon between the surface and the atmosphere is that due to the combustion of fossil fuels and cement production, recently estimated at 8.4 PgC year -1 (U.S. share is 1.6 PgC year -1 ) for the year 2006 (10,3).…”

“…In most cases, little subnational allocation of the emissions was performed because the initial purposeunderstanding 20 th century global climate change -required little sub-national information. Thus, the most common spatiotemporal distribution of fossil fuel CO 2 emissions occurred at an annual timescale and at the national spatial scale. Starting in the 1980s, research was begun to further subdivide these emissions into finer spatial and temporal scales (6).…”

Storage and Turnover of Organic Matter in Soil

“…Project, or C 4 MIP), all but one of eleven models predicted faster decomposition rates with climate change to 2100 (Friedlingstein 2006). Because modeled NPP did not increase commensurately, most of these simulations predicted decreases or no change in soil carbon stocks and a positive feedback with climate change.…”

The Origin and Limits of the Near Proportionality between Climate Warming and Cumulative CO2 Emissions

“…TCRE expands the quantification of transient response to anthropogenic emissions by amalgamating the notion of carbon sensitivity with TCR ). Carbon sensitivity describes the fraction of emitted carbon that remains in the atmosphere given the strength of carbon cycle feedbacks at a given point in time (Friedlingstein et al 2006). By combining these two quantities, one can directly relate CO 2 emissions to near-surface temperature change.…”