The Carbon Budget Reconciliation Challenge - A Joint ESA-NASA Initiative

Despite efforts by the international carbon cycle research community there remain significant differences between the global carbon budget and regionally aggregated budgets of the key greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). These differences relate to the complexity of the carbon cycle, its interactions with other cycles but also differences in methods and data used to generate the budgets. The principal budget calculations are also out of synchrony, with an annual (CO₂) budget, and global CH₄ and N₂O budgets on a longer cycle and the Regional Carbon Assessment (RECCAP) developed every five years.

The challenge for the International Community is:

• to align budget calculations in time
• reconcile the global and regional assessments across the three GHG gases.
• develop regional budget updates for the three GHG gases.

New datasets and satellite-based opportunities are emerging that may contribute to this challenge. Space-based measurements of atmospheric concentrations of CO₂ and CH₄ and observations of both the terrestrial and ocean carbon cycle are increasing in frequency, range, and detail. With the planned launches of key carbon relevant satellites by NASA, ESA and others, these observations will provide a unique capability to provide a dynamic reconstruction of the carbon cycle at unprecedented scales in space and time.

The ESA-NASA Carbon Budget Reconciliation Initiative has been established to help coordinate the EO satellite contributions to RECCAP and GCB internationally by:

• providing a satellite ‘backbone’ to help resolve current discrepancies between global and regional GHG budget estimates.
• providing key satellite-based updates on carbon cycle state and change, with appropriate latency, in the periods between the current and future RECCAP exercises.
• providing training for the next generation of carbon cycle scientists in preparation for future global and regional budget assessments.

Discussions will provide a forum for understanding new observations and GHG reporting methods.