Unlike elsewhere on the globe, temperature in the tropics has increased systematically. From observed tropical temperature, numerical simulations have reproduced the observed evolution of atmospheric CO2, including its annual cycle. Much the same has followed empirically from the observed covariance between tropical temperature and net emission of CO2 – the component of emission that actually changes CO2. Intensified over tropical land, the robust coherence between those observed features establishes that the changes of tropical temperature do not follow from changes of CO2, but rather produce them.
Here, we investigate the physical mechanisms through which observed warming in the tropics
can produce the observed evolution of CO2. The conservation law governing atmospheric CO2, supported by the observed temperature dependence of surface fluxes and observed temperature in the tropics, is used to calculate the time-varying response of CO2 net emission.
Thermally-induced emission is found to account for the preponderance of CO2 net emission and, thereby, for the vast majority of anomalous CO2. Magnified over tropical land, it represents interannual intensifications of net emission, notably during episodes of El Niño. Represented equally well is the long-term intensification of net emission during the last half century. That intensification alone accounts for about half of the observed increase of atmospheric CO2. Anomalous CO2 introduced by the calculated net emission closely tracks the observed evolution of atmospheric CO2.
Having similar dependence on temperature is methane. Like net emission of CO2, net emission of methane is intensified by tropical warming. The simultaneous intensification of CO2 and CH4 emission provides a unified understanding of their joint increase, one that follows naturally from thermally-induced emission.
Continue reading: Theory of Increasing Greenhouse Gases. By Murry Salby and Hermann Harde.