New Insights From OCO-2 Showcased in Science

High-resolution satellite data from NASA’s Orbiting
Carbon
Observatory-2 are revealing the subtle ways that carbon
links everything on
Earth – the ocean, land, atmosphere,
terrestrial ecosystems and human
activities. Scientists using
the first 2 1/2 years of OCO-2 data have published
a special
collection of five
papers today in the journal Science that
demonstrates the breadth of this
research. In addition to
showing

how drought and heat in tropical forests
affected global
carbon dioxide levels

during the 2015-16
El Niño, other results from these papers focus on ocean carbon
release and absorption, urban emissions and a new way to study
photosynthesis.
A final paper by OCO-2 Deputy Project
Scientist Annmarie Eldering of NASA’s Jet
Propulsion
Laboratory in Pasadena, California, and colleagues gives an
overview
of the state of OCO-2 science.

Emissions From Individual Cities and
Volcanoes
Visible From Space

More than 70
percent of carbon dioxide emissions from
human activities comes from cities,
but because the gas mixes
rapidly into the atmosphere, urban emissions are
challenging
to isolate and analyze.
Florian
Schwandner of JPL
and colleagues used OCO-2 observations to detect how carbon
dioxide emissions vary around
individual
cities
— the first time this has been done with data collected in
just a few
minutes from space. Over Los Angeles and the
surrounding area, they were able
to detect differences as
small as 1 percent of total atmospheric carbon dioxide
concentrations within the air column below the
satellite.

The
OCO-2 measurements across Los Angeles were detailed
enough to capture
differences in concentrations within the
city resulting from localized sources.
They also tracked
diminishing carbon dioxide concentrations as the spacecraft
passed from over the crowded city to the suburbs and out to the
sparsely populated
desert to the north.

OCO-2’s
orbit also allowed it to observe significant
carbon dioxide signals from isolated
plumes of three volcanoes
on the Pacific island nation of Vanuatu. One orbit
directly
downwind of Mt. Yasur, which has been erupting persistently
since at
least the 1700s, yielded a narrow string of carbon
dioxide that was about 3.4 parts
per million higher than
background levels — consistent with emissions of 41.6
kilotons of carbon dioxide a day. This
is a valuable
quantification of volcanic emissions, which are small compared
to
the average human emissions of about 100,000 kilotons per
day.

El Niño Suppressed Tropical Ocean’s
Release of
Carbon

Abhishek Chatterjee of NASA’s Goddard Space Flight Center
in Greenbelt,
Maryland, and colleagues studied how the big
2015-16 El Niño affected carbon
dioxide over the tropical
Pacific Ocean.

This ocean region is usually a source of carbon dioxide
to the
atmosphere. As part of global ocean circulation, cold,
carbon-dioxide-rich
water wells up to the surface in this
region, and the extra carbon dioxide
outgasses to the
atmosphere. Because El Niño events suppress this upwelling,
scientists have conjectured that it reduces the ocean’s carbon
dioxide
emissions and therefore causes a slowdown in the
growth rate of atmospheric
carbon dioxide concentrations.
However, until OCO-2, there haven’t been
adequate atmospheric
observations over the remote tropical Pacific to confirm
this
theory.

OCO-2 data show that in the first few months of the
2015-16 El
Niño, the rate of carbon dioxide released from the
tropical Pacific to the
atmosphere decreased by 26 to 54
percent. That translates to a short-term reduction
of 0.4 to
0.5 parts per million in atmospheric concentration, or close to
0.1
percent of total atmospheric carbon dioxide.

A change of one-tenth of one percent in carbon dioxide
may sound
negligible, but it occurred over a region in the
Pacific Ocean about the size
of the entire continent of
Australia. This reduction in carbon dioxide
emissions for a
few months was strong enough that it could be observed by
OCO-2
and the National Oceanic and Atmospheric
Administration’s Tropical Pacific
Observing System of buoys,
which directly measure carbon dioxide concentrations
at the
surface of the ocean. The record uptick in atmospheric carbon
dioxide
that occurred in 2015 and 2016 would have been even
greater without this
decrease in tropical Pacific Ocean
emissions.

With OCO-2, scientists can observe these tiny changes for
the
first time, a first step toward understanding the
sensitivity of the carbon
cycle to climate variations on a
scale of years to decades.

A
New Way to Measure Photosynthesis

Besides
carbon dioxide, OCO-2’s high-resolution
spectrometers can observe solar-induced
fluorescence, or SIF.
This radiation, emitted by chlorophyll molecules in
plants,
indicates that photosynthesis is occurring. SIF provides
valuable
insight into global photosynthesis because it
captures photosynthesis during
the growing season and also its
slowdown, for example, over evergreen forests
in winter, when
trees maintain chlorophyll but stop absorbing carbon dioxide
from the atmosphere.

Ying
Sun of Cornell University in Ithaca, New York, and
colleagues report on OCO-2’s
unique SIF measurements, which
provide a much higher spatial resolution than
any previous
system. The improved resolution enabled the scientists to
perform
the first-ever validation of SIF from concurrent
airborne observations.

OCO-2’s
smaller image “footprint” on Earth allowed the
researchers to do a
more direct comparison of the satellite
measurements with ground-based
measurements of flows of carbon
dioxide between plants and the air.
They found a consistent
relationship between SIF and carbon dioxide uptake in
plants
across different types of ecosystems. This finding sets the
direction
for in-depth studies that may further illuminate the
relationship between SIF
and global photosynthesis.

News Media Contact

Alan Buis
Jet Propulsion Laboratory, Pasadena, California
818-354-0474
Alan.Buis@jpl.nasa.gov

Steve Cole
NASA Headquarters, Washington
202-358-0918
Stephen.e.cole@nasa.gov

Written by Carol Rasmussen
NASA’s Earth Science News Team

2017-268

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