Abstract
The atmospheric CO2 growth rate (CGR) variability is largely controlled by tropical temperature fluctuations. The sensitivity of CGR to tropical temperature left({{{{rm{gamma }}}}}_{{{{rm{CGR}}}}}^{{{{rm{T}}}}}right) has strongly increased since 1960, but here we show that this trend has ceased. Here, we use the long-term CO2 records from Mauna Loa and the South Pole to compute CGR, and show that {{{{rm{gamma }}}}}_{{{{rm{CGR}}}}}^{{{{rm{T}}}}} increased by 200% from 1960–1979 to 1979–2000 but then decreased by 117% from 1980–2001 to 2001–2020, almost returning back to the level of the 1960s. Variations in {{{{rm{gamma }}}}}_{{{{rm{CGR}}}}}^{{{{rm{T}}}}} are significantly correlated with changes in precipitation at a bi-decadal scale. These findings are further corroborated by results from a dynamic vegetation model, collectively suggesting that increases in precipitation control the decreased {{{{rm{gamma }}}}}_{{{{rm{CGR}}}}}^{{{{rm{T}}}}} during recent decades. Our results indicate that wetter conditions have led to a decoupling of the impact of the tropical temperature variation on the carbon cycle.
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