CMP4 – Developing a tropical carbon cycle observatory for Amazon and Africa

Tropical land regions are key components of the coupled carbon cycle climate system because of the large sizes of their carbon pools, particularly rainforests, the potential for human alteration and for positive climate feedbacks. Despite this it is widely recognised that it is precisely these regions where the largest observational gaps remain. This has effectively prevented robust CCDAS activities for these regions, for example, there is not even agreement on the sign of the net tropical terrestrial flux. Indeed the only true integrator of all surface CO2 fluxes, the atmosphere, is very poorly sampled in the tropics, particularly over tropical land. Similarly key characteristics of land vegetation functioning remain to be determined, like e.g. the western Amazon basin characterised by relatively rich soils. The great uncertainty of the net carbon balance and trends of tropical land carbon pools is also a key stumbling block towards a truly global view and synthesis of the state and trajectory of the carbon cycle.

The focus of CMP4 is towards closing this tropical data gap, with a major South American component and an innovative African component by building on and extending current recently established measurement programs.

The overall strategy followed in the CMP is to provide the large-scale flux integrating constraint, the troposphere GHG (Greenhouse Gas) concentration distribution in space and time, through vertical aircraft profile GHG sampling with sectoral estimates of pools and pool changes. These include those of old-growth forests including their natural disturbance processes and recovery, those related to land-use change and fire, and those related to river out-gassing based on measurements available through the NERC AMAZONICA project for tropical South America. We will also provide major novel constraints on ecosystem functioning closing key remaining knowledge gaps. All these data constraints will then feed into CCDAS systems – both at the global (CMP2) but also at the regional scale (Amazon and tropical Africa). Regional CCDAS are attractive because they permit high resolution in space and time, and avoid at the same time propagation of potential atmospheric transport biases from far-remote regions. Altogether the new data and CCDAS systems are designed to provide a coherent assessment of the Carbon Cycle in the two major regions of the tropics, thereby advancing substantially our knowledge of the carbon cycle. CMP4 is also to “provide long-term possibilities for sustaining such a system beyond its research and development phase,” as the call for 6.4.1 requests.

Furthermore, in conjunction with CMP1, this Component will build on existing regional initiative and resource to generate new observations to produce pan-tropical datasets for assimilation, as highlighted as the ‘Expected Impacts’ in the call. Finally CMP4 will share a post-doctoral researcher with CMP2 to advance a regional CCDAS for tropical South America and Africa exploiting fully these large-scale observational data.