evidence: In his second claim, Dr. Plimer posits that the present-day atmospheric CO2 increase is from the ocean releasing CO2 in response to past natural warming, not human emissions. However, this claim fundamentally overlooks multiple sources of evidence showing a massive influx of anthropogenic CO2 to the climate system. While the ocean does respond to warmer temperatures by outgassing CO2 during glacial-interglacial transitions on timescales of hundreds-to-thousands of years, this mechanism does not explain observations of the rapid and unprecedented rise of atmospheric CO2 concentrations since the onset of the industrial era. [...] Several atmospheric measurements provide further corroboration that human emissions are the source of rising global atmospheric CO2 concentrations[4],[10]. Figure 5, top, shows observations of monthly CO2 concentrations at Mauna Loa Observatory and the South Pole, with concentrations at both stations continuously increasing since measurements began in the late-1950s. Another feature is that CO2 concentrations at Mauna Loa have increased by a few ppm compared to the South Pole, indicating higher CO2 input from the land-dominated northern hemisphere, where most industrialized regions are located. Furthermore, measured atmospheric oxygen (O2) concentrations have been steadily decreasing globally since regular observations began around 1990 (Fig. 5, bottom). Atmospheric O2 concentrations are not affected by ocean CO2 outgassing, so the decreasing O2 concentrations indicate that increasing atmospheric CO2 is primarily driven by an oxygen-consuming process, namely combustion, but also respiration.