Narrowing the spread in CMIP5 model projections of air-sea CO2 fluxes.

Lei Wang,Zongci Zhao,Yong Luo,Jianbin Huang

doi:10.1038/srep37548

Abstract

Large spread appears in the projection of air-sea CO2 fluxes using the latest simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Here, two methods are applied to narrow this spread in 13 CMIP5 models. One method involves model selection based on the ability of models to reproduce the observed air-sea CO2 fluxes from 1980 to 2005. The other method involves constrained estimation based on the strong relationship between the historical and future air-sea CO2 fluxes. The estimated spread of the projected air-sea CO2 fluxes is effectively reduced by using these two approaches. These two approaches also show great agreement in the global ocean and three regional oceans of the equatorial Pacific Ocean, the North Atlantic Ocean and the Southern Ocean, including the average state and evolution characteristics. Based on the projections of the two approaches, the global ocean carbon uptake will increase in the first half of the 21st century then remain relatively stable and is projected to be 3.68–4.57 PgC/yr at the end of 21st century. The projections indicate that the increase in the CO2 uptake by the oceans will cease at the year of approximately 2070.

Highlights

Large spread appears in the projection of air-sea CO2 fluxes using the latest simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5)
Using model selection and constrained estimation, the spread projected by CMIP5 models in 21st century is effectively reduced
The carbon sink capacity of the global ocean will increase with the rapid increase in atmospheric CO2 concentrations in the first half of the 21st century and will remain stable with no further growth after approximately 2070

Summary

Methods and Results

We analyzed the air-sea CO2 fluxes simulated by the 13 CMIP5 models that provide both “esmhistorical” simulations and “esmrcp85” projection simulations. In addition to the global ocean, three important regional oceans – the equatorial Pacific Ocean, North Atlantic Ocean and Southern Ocean – are analyzed independently. Total air-sea CO2 fluxes (units: PgC/yr) Global Ocean Equatorial Pacific Ocean North Atlantic Ocean Southern Ocean. The air-sea CO2 fluxes, the largest atmospheric CO2 source region is the equatorial Pacific Ocean, which is located between 30°S and 10°N and releases approximately 40% of the total CO2 emissions from the global ocean. The net fluxes composed of the absorption and emission south of 40°S are considered as the air-sea CO2 fluxes in Southern Ocean, which overall acts as a large atmospheric CO2 sink. A large spread in the simulated total air-sea CO2 fluxes remains in both the historical (1861–2005) and future (2006–2099) projected periods.

Multiples of σSelected models

Conclusion and Discussion

Author Contributions

Additional Information