The annual variation of atmospheric CO₂ concentration observed in the northern hemisphere

Abstract

Records of the annual variation of the atmospheric carbon dioxide concentration at Mauna Loa, Point Barrow, and Weathership P are examined for secular changes. The amplitude of the annual variation appears to have increased in recent years with a best estimate of the rate of change, based on the Mauna Loa data, of 0.45±0.42% yr−1. This change is discussed in terms of changes in biospheric respiration and photosynthesis and the use of fossil fuels. The analysis does not allow for the separation of several possible causes of amplitude change. However, if the change is interpreted as reflecting enhanced biospheric growth, the effect is equivalent to a 8% change in the net summer uptake of carbon over the years 1959–1978 and to a growth of the northern hemisphere seasonal biosphere of 0.5×1012 kg of carbon per year. Such a conclusion is consistent with recent inventory studies, which indicate that temperate zone forests have acted as a net sink of about 1012 kg of carbon per year in recent decades.

Downward Regulation of Photosynthesis and Growth at High CO2 Levels

“…Indeed, when Havelka et al (7) grew soybeans in the field, in clear-plasticwall open-top chambers such as ours, they measured significantly higher net photosynthesis rates in their C02-enriched plants throughout the entire growing season, which they noted was "in contrast to some [and they could well have said "most"] published data." Likewise, whereas Mauney et al (16) Essentially everyone who has studied this phenomenon has acknowledged that the only plausible explanation for the increasing amplitude of the air's annual CO2 cycle is that the photosynthetic activity of the world's plant life is growing ever more robust as a result ofthe ever-increasing CO2 content ofthe atmosphere (3,4,13,18 In view of these observations, we feel that downward regulation of photosynthesis and growth at high CO2 levels may be an experimental artifact of the manner in which most CO2 enrichment studies have been conducted. As such a finding would have profound implications for terrestrial carbon sequestering, in view of the potential for CO2-induced greenhouse warming, further study of this important topic should be a high priority of future research.…”

CO2-induced global warming: a skeptic's view of potential climate change

“…Because of this stimulatory effect of elevated carbon dioxide on plant growth and development, the productivity of the biosphere has been rising hand-in-hand with the recent historical rise in the air's CO 2 content (Idso 1995), as is evident in (1) the ever-increasing amplitude of the seasonal cycle of the air's CO 2 concentration (Pearman & Hyson 1981, Cleveland et al 1983, Bacastow et al 1985, Myneni et al 1997, (2) the upward trends in a number of long tree-ring records that mirror the progression of the Industrial Revolution (LaMarche et al 1984, Graybill & Idso 1993, and (3) the accelerating growth rates of numerous forests on nearly every continent of the globe over the past several decades (Kauppi et al 1992, Phillips & Gentry 1994, Pimm & Sugden 1994, Idso 1995.…”

Drivers of multi-century trends in the atmospheric CO<sub>2</sub> mean annual cycle in a prognostic ESM

“…The amplitude of the mean annual cycle of atmospheric CO 2 , an indicator of seasonal terrestrial and ocean carbon exchange, has increased over the Northern Hemisphere (NH) since observational records began in the late 1950s (Pearman and Hyson, 1981;Cleveland et al, 1983;Bacastow et al, 1985;Conway et al, 1994;Keeling et al, 1996;Randerson et al, 1997;Graven et al, 2013;Liu et al, 2015). The largest increases of 40-50 % were observed over the northern high latitudes via surface monitoring (Keeling et al, 1996) and from aircraft observations of the free troposphere (Graven et al, 2013).…”