Watching the Earth breath from space: OCO-2 and measuring CO2

The OCO-2, aka, Orbiting Carbon Observatory 2, is a satellite that measures CO2 in the atmosphere, using a spectrograph.

From a news article in today’s Science, “One of the crowning achievements of modern environmental science is the Keeling curve, the detailed time series of the concentration of atmospheric carbon dioxide (CO2) begun in 1958 that has enabled deep insights into the mechanisms of global climate change. These measurements were difficult to make for most of their 60-year history, involving the physical collection of air samples in flasks at a small number of sites scattered strategically around the globe and the subsequent analysis of their CO2 inventories in a handful of laboratories throughout the world.”

The purpose of the OCO-2 was to make these measurements much more accurate and efficient, and to provide more granularity in the details. The space craft was launched in July 2014, replacing an earlier OCO (OCO-1, if you like) which was launched in 2009.

Do not tell Donald Trump about this satellite. He’ll have it shot down.

Anyway, the current issue of Science is a collection of papers that provide the initial OCO-2 results, “covering the detection of CO2 emissions from specific point sources; measurements of CO2 variations associated with El Niño, on land and at sea; and solar-induced fluorescence measurements of photosynthesis for determining gross primary production by plants.”

There has been material published already, listed here.

Here I’m just going to give you the highlights of some of the results, cribbed from a selection of the various papers. You’ll want to get a copy of this issue of Science, at the library, to head into the weeds.

From Contrasting carbon cycle responses of the tropical continents to the 2015–2016 El Niño by Liu et al,

Our results indicate that the global El Niño effect is a superposition of regionally specific effects. The heterogeneous climate forcing and carbon response over the three tropical continents to the 2015–2016 El Niño challenges previous studies that suggested that a single dominant process determines carbon cycle interannual variability, which could also be due to previous disturbance and soil and vegetation structure. The similarity between the 2015 tropical climate anomaly and the projected climate changes imply that the role of the tropical land as a buffer for fossil fuel emissions may be reduced in the future.

From The Orbiting Carbon Observatory-2 early science investigations of regional carbon dioxide fluxes by Eldering et al:

Earth’s carbon cycle involves large fluxes of carbon dioxide (CO2) between the atmosphere, land biosphere, and oceans. Over the past several decades, net loss of CO2 from the atmosphere to the land and oceans has varied considerably from year to year, equaling 20 to 80% of CO2 emissions from fossil fuel combustion and land use change. On average, the uptake is about 50%. The imbalance between CO2 emissions and removal is seen in increasing atmospheric CO2 concentrations….The measurements from OCO-2 provide a global view of the seasonal cycles and spatial patterns of atmospheric CO2, with the anticipated year-over-year growth rate. The buildup of CO2 in the Northern Hemisphere during winter and its rapid decrease in concentration as spring arrives (and the SIF increases) is seen in unprecedented detail. The enhanced CO2 in urban areas relative to nearby background areas is observed with a single overpass of OCO-2. Increases in CO2 due to the biomass burning in Africa are also clearly observed.

From OCO-2 advances photosynthesis observation from space via solar-induced chlorophyll fluorescence by Sun et al:

Reliable estimation of gross primary production (GPP) from landscape to global scales is pivotal to a wide range of ecological research areas, such as carbon-climate feedbacks, and agricultural applications, such as crop yield and drought monitoring. However, measuring GPP at these scales remains a major challenge. Solar-induced chlorophyll fluorescence (SIF) is a signal emitted directly from the core of photosynthetic machinery. SIF integrates complex plant physiological functions in vivo to reflect photosynthetic dynamics in real time. The advent of satellite SIF observation promises a new era in global photosynthesis research. The Orbiting Carbon Observatory-2 (OCO-2) SIF product is a serendipitous but critically complementary by-product of OCO-2’s primary mission target—atmospheric column CO2 (Embedded Image). OCO-2 SIF removes some important roadblocks that prevent wide and in-depth applications of satellite SIF data sets and offers new opportunities for studying the SIF-GPP relationship and vegetation functional gradients at different spatiotemporal scales.

Our analyses suggest that SIF is a powerful proxy for GPP at multiple spatiotemporal scales and that high-quality satellite SIF is of central importance to studying terrestrial ecosystems and the carbon cycle. Although the possibility of a universal SIF-GPP relationship across different biome types cannot be dismissed, in-depth process-based studies are needed to unravel the true nature of covariations between SIF and GPP. Of critical importance in such efforts are the potential coordinated dynamics between the light-use efficiencies of CO2 assimilation and fluorescence emission in response to changes in climate and vegetation characteristics. Eventual synergistic uses of SIF with atmospheric CO2 enabled by OCO-2 will lead to more reliable estimates of terrestrial carbon sources and sinks—when, where, why, and how carbon is exchanged between land and atmosphere—as well as a deeper understanding of carbon-climate feedbacks.

From Influence of El Niño on atmospheric CO2 over the tropical Pacific Ocean: Findings from NASA’s OCO-2 mission, by Chatterjee et al:

The Orbiting Carbon Observatory-2 (OCO-2) is NASA’s first satellite designed to measure atmospheric carbon dioxide (CO2) with the precision, resolution, and coverage necessary to quantify regional carbon sources and sinks. OCO-2 launched on 2 July 2014, and during the first 2 years of its operation, a major El Niño occurred: the 2015–2016 El Niño, which was one of the strongest events ever recorded.

El Niño and its cold counterpart La Niña (collectively known as the El Niño–Southern Oscillation or ENSO) are the dominant modes of tropical climate variability. ENSO originates in the tropical Pacific Ocean but spurs a variety of anomalous weather patterns around the globe. Not surprisingly, it also leaves an imprint on the global carbon cycle. Understanding the magnitude and phasing of the ENSO-CO2 relationship has important implications for improving the predictability of carbon-climate feedbacks.

The high-density observations from NASA’s OCO-2 mission, coupled with surface ocean CO2 measurements from NOAA buoys, have provided us with a unique data set to track the atmospheric CO2 concentrations and unravel the timing of the response of the ocean and the terrestrial carbon cycle during the 2015–2016 El Niño….

The strong El Niño event of 2015–2016 provided us with an opportunity to study how the global carbon cycle responds to a change in the physical climate system. Space-based observations of atmospheric CO2, such as from OCO-2, allow us to observe and monitor the temporal sequence of El Niño–induced changes in CO2 concentrations. Disentangling the timing of the ocean and terrestrial responses is the first step toward interpreting their relative contribution to the global atmospheric CO2 growth rate, and thereby understanding the sensitivity of the carbon cycle to climate forcing on interannual to decadal time scales.

From Spaceborne detection of localized carbon dioxide sources b Schwander et al:

Although the carbon budget is often presented in terms of global-scale fluxes, many of the contributing processes occur through localized point sources, which have been challenging to measure from space. Persistent anthropogenic carbon dioxide (CO2) emissions have altered the natural balance of Earth’s carbon sources and sinks. These emissions are driven by a multitude of individual mobile and stationary point sources that combust fossil fuels, with urban areas accounting for more than 70% of anthropogenic emissions to the atmosphere. Natural point-source emissions are dominated by wildfires and persistent volcanic degassing.

Spaceborne measurements of atmospheric CO2 using kilometer-scale data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) reveal distinct structures caused by known anthropogenic and natural point sources, including megacities and volcanoes. Continuous along-track sampling across Los Angeles (USA) by OCO-2 at its ~2.25-km spatial resolution exposes intra-urban spatial variability in the atmospheric Embedded Image distribution that corresponds to the structure of the urban dome, which is detectable under favorable wind conditions. Los Angeles Embedded Image peaks over the urban core and decreases through suburban areas to rural background values more than ~100 km away. Enhancements of Embedded Image in the Los Angeles urban CO2 dome observed by OCO-2 vary seasonally from 4.4 to 6.1 parts per million (ppm). We also detected isolated CO2 plumes from the persistently degassing Yasur, Ambrym, and Aoba volcanoes (Vanuatu), corroborated by near-simultaneous sulfur dioxide plume detections by NASA’s Ozone Mapping and Profiler Suite. An OCO-2 transect passing directly downwind of Yasur volcano yielded a narrow filament of enhanced Embedded Image (Embedded Image ? 3.4 ppm), consistent with plume modeling of a CO2 point source emitting 41.6 ± 19.7 kilotons per day (15.2 ± 7.2 megatons per year). These highest continuous volcanic CO2 emissions are collectively dwarfed by about 70 fossil fuel–burning power plants on Earth, which each emit more than 15 megatons per year of CO2.

OCO-2’s sampling strategy was designed to characterize CO2 sources and sinks on regional to continental and ocean-basin scales, but the unprecedented kilometer-scale resolution and high sensitivity enables detection of CO2 from natural and anthropogenic localized emission sources. OCO-2 captures seasonal, intra-urban, and isolated plume signals. Capitalizing on OCO-2’s sensitivity, a much higher temporal resolution would capture anthropogenic emission signal variations from diurnal, weekly, climatic, and economic effects, and, for volcanoes, precursory emission variability. Future sampling strategies will benefit from a continuous mapping approach with the sensitivity of OCO-2 to systematically and repeatedly capture these smaller, urban to individual plume scales of CO2 point sources.

Wow, that’s a lot of Science in one day. All from THIS issue.

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