A two-fold increase of carbon cycle sensitivity to tropical temperature variations

Area of Science:

• Climate Science
• Earth System Science
• Carbon Cycle Research

Background:

• Earth system models predict a shrinking tropical land carbon sink due to warming and drought, potentially creating a positive climate feedback.
• Limited data currently hinders testing of these predictions regarding tropical carbon balance shifts.
• Long-term atmospheric carbon dioxide data offer a global record integrating interannual variability, largely driven by the terrestrial biosphere.

Observation:

• Year-to-year variations in the atmospheric carbon dioxide growth rate (CGR) are primarily linked to tropical land carbon flux fluctuations.
• Analysis of Mauna Loa and South Pole CGR records reveals a significant increase in CGR sensitivity to tropical temperature variability over the past five decades.
• This sensitivity has amplified by a factor of 1.9 ± 0.3, indicating a heightened response of the carbon sink to temperature changes.

Findings:

• The sensitivity of CGR to interannual temperature variations has demonstrably increased over the last 50 years.
• This temperature sensitivity is amplified under drier conditions in tropical land regions, suggesting moisture regulation.
• Existing terrestrial carbon cycle models do not accurately represent the observed enhancement in CGR sensitivity.

Implications:

• Enhanced CGR sensitivity in tropical ecosystems indicates a potentially stronger positive climate feedback than previously modeled.
• The regulatory role of moisture highlights the complex interactions within the tropical carbon cycle.
• Improved understanding of tropical ecosystem responses to drought and warming is crucial for accurate future climate and carbon cycle projections.