How Well Do We Understand the Land‐Ocean‐Atmosphere Carbon Cycle?

Abstract

Fossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO2) abundance by about 50% since the beginning of the industrial age. The atmospheric CO2 growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO2. As these CO2 emissions grew, uptake by the ocean increased in response to increases in atmospheric CO2 partial pressure (pCO2). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO2 uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid‐ and high‐latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship‐based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean‐atmosphere fluxes and interior ocean carbon storage on policy‐relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO2 in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.

Tracking CO2 emission reductions from space: A case study at Europe’s largest fossil fuel power plant

“…Here we present the quantification of CO 2 emission reductions at the European Union's largest CO 2 point source, the Bełchatów Power Station in Poland, by adapting the Nassar et al (2021) method for the Orbiting Carbon Observatory 3 (OCO-3), thus demonstrating CO2M's second objective in a case study on a large power plant. Baseline CO 2 observations near Bełchatów were made in March 2017 with OCO-2 (Nassar et al, 2021;Crisp et al, 2022). Using the new CO 2 mapping capability of OCO-3 (Taylor et al, 2020) at Bełchatów from April 2020 to June 2022, we determine emission reductions consistent with reported hourly power generation changes.…”

Explicit Physical Knowledge in Machine Learning for Ocean Carbon Flux Reconstruction: The pCO2‐Residual Method

“…Observation-based products that incorporate observations of surface ocean pCO 2 include both natural and anthropogenic carbon in the resulting pCO 2 and CO 2 flux product. This is the net CO 2 flux (F net = F natural + F ant ) (Crisp et al, 2022). The natural outgassing of riverine carbon is understood to be the dominant component of F natural (Aumont et al, 2001;Crisp et al, 2022;Hauck et al, 2020).…”

“…This is the net CO 2 flux (F net = F natural + F ant ) (Crisp et al, 2022). The natural outgassing of riverine carbon is understood to be the dominant component of F natural (Aumont et al, 2001;Crisp et al, 2022;Hauck et al, 2020). Additional non-riverine components such as outgassing due to ocean circulation change have been proposed for 1994-2007 (Gruber et al, 2019), with large uncertainty in magnitude and no evidence of long-term impact (Crisp et al, 2022); these are assumed to be zero here.…”

“…Since the beginning of the Industrial Revolution, the ocean has absorbed about a third of the total anthropogenic emissions (Khatiwala et al, 2013;Sabine et al, 2004). The processes governing the large-scale distribution of ocean pCO 2 and the drivers of seasonality are well understood (Crisp et al, 2022;Takahashi et al, 2002Takahashi et al, , 2009). Yet, the quantification of year-to-year variability and long-term changes in this carbon sink remains a challenge (…”

On the use of Earth Observation to support estimates of national greenhouse gas emissions and sinks for the Global stocktake process: lessons learned from ESA-CCI RECCAP2

“…The past few years have seen a drastic increase in EO data available for monitoring the atmospheric concentration of trace gases, vegetation cover, status and biomass and other relevant ECVs such soil-moisture, fires, permafrost, etc. [ 16 , 28 , 74 ].…”