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The Increasing Land Sink of the Northern Hemisphere

Paper Reviewed
Ciais, P., Tan, J., Wang, X., Roedenbeck, C., Chevallier, F., Piao, S.-L., Moriarty, R., Broquet, G., Le Quéré, C., Canadell, J.G., Peng, S., Poulter, B., Liu, Z. and Tans, P. 2019. Five decades of northern land carbon uptake revealed by the interhemispheric CO2 gradient. Nature 568: 221-225.

Regular readers of CO2 Science know that there are three key benefits of atmospheric CO2 enrichment, including the plant productivity gains that result from the aerial fertilization effect, plus its transpiration-reducing effect that boosts plant water use efficiency, along with its stress-alleviating effect that lessens the negative growth impacts of resource limitations and environmental constraints. Consequently, we have long maintained that the world's vegetation possesses an ideal mix of abilities to reap a tremendous benefit in response to the atmosphere’s increasing carbon dioxide concentration.

Over the past decade or so, more and more research has been published confirming this hypothesis. Real-world evidence (primarily found in satellite data) points to a great greening of the Earth, as it is often called. But what is most surprising about these observations is the fact that they are even occurring at all —- if you accept the claims of climate alarmists.

Consider, for example, their concerns that since 1980 the Earth has weathered four of the warmest decades in the modern instrumental temperature record, as well as a handful of intense and persistent El Niño events, large-scale deforestation, “unprecedented” forest fires, and episodes of persistent, widespread and severe drought. At the same time, the air’s CO2 content has increased by more than 16% and the human population has grown by over 55%. To global warming alarmists, as well as most journalists and media personnel, the Earth is presently in the throes of a veritable climate Armageddon, doomed and destined for failure because of the aforementioned tragedies.

Of course, concerns about the demise of the terrestrial biosphere are consistently and vastly overstated to the point that observations show just the opposite to be occurring. The section Biospheric Productivity (Global: The Recent Past) in our website’s Subject Index, for example, houses links to reviews of numerous scientific articles published in peer-reviewed journals showing the whole of the terrestrial biosphere is more robust now than at any other time during the Modern Era. And, again, this enhancement has occurred despite the many real and imagined assaults on nature claimed by climate alarmists.

The latest study to further confirm a recent improvement in the vegetative state of the terrestrial biosphere comes from Ciais et al. (2019). Writing in the journal Nature, the fourteen researchers examined five decades of carbon uptake in the Northern Hemisphere using measurements of the interhemispheric gradient of atmospheric CO2 over the period 1958-2016.

The results of their analysis revealed that “the northern land sink remained stable between the 1960s and the late 1980s, then increased by 0.5 ± 0.4 petagrams of carbon per year during the 1990s and by 0.6 ± 0.5 petagrams of carbon per year during the 2000s” (see Figure 1). In regard to this finding, Ciais et al. note that the increasing land sink of the Northern Hemisphere “can be explained by a combination of increasing concentrations of atmospheric carbon dioxide, climate variability and changes in land cover” during the decades of the 1960s through 1990s. After that time (2000-2016), they note the increase is “underestimated by all models, which suggests the need for improved consideration of changes in drivers such as nitrogen deposition, diffuse light and land-use change,” to which we would also add the CO2 fertilization effect, the magnitude of which the models all undervalue. Regardless of the cause or causes behind the recent vegetative enhancement of the Northern Hemisphere, the fact that it has increased over the past five decades reveals the doomsayers have been and continue to be wrong in their estimate of the consequences of rising atmospheric CO2.

Figure 1. Northern Hemisphere land sink (LN) over the period 1958-2016 inferred from a two-box inversion model constrained by measurements of the interhemispheric CO2 gradient and the ocean sink interhemispheric difference from ocean models. Source: Ciais et al. (2019).

Posted 23 July 2019