SCIENCE science.orgsions across more than 250,000 facilities in
California reported that 30 of those emit-
ters were responsible for 20% of the total
methane emission in the state ( 9 ).
Lauvaux et al. identified the leaders
among these super-emitters—the so-called
“ultra-emitters.” Using global data collected
by the TROPOMI satellite over several years,
the authors assembled a list of ultra-emitter
sites responsible for a total of roughly 8 mil-
lion tonnes of methane per year, with the
warming potential equivalent to 250 mil-
lion tonnes of CO 2 ( 10 ). To put this into per-
spective, 250 million tonnes of CO 2 is the
carbon footprint of more than 40 million
people. This finding is even more notable
when one considers that the TROPOMI sat-
ellite was not designed to track emissions
at the facility scale. However, the amount
of emission from these ultra-emitters is so
large that TROPOMI could track it with a
spatial resolution in the 5-km range.
Researchers have quantified CO 2 emis-
sions from super-emitters by comparing
land-based measurements with satellite-
based estimates, and combining those val-
ues with calculations of downwind plume
concentrations using atmospheric modeling
( 11 ). However, in contrast to CO 2 , the loca-
tions and emissions of major methane emit-
ters are difficult to track, as methane emis-
sions are an unwanted by-product of the oil
and gas industry and often go unreported.
The creation of a global inventory of meth-
ane ultra-emitters provides crucial informa-
tion for targeting the strongest emitters. This
should be a useful arsenal for policy-makers
to enact effective regulations to combat cli-
mate change and alleviate climate-related
economic calamity in the long run.
Given the 3 years left in the designed op-
erational life span of TROPOMI, the project
will continue to provide data for monitor-
ing the known ultra-emitters and detecting
new ones. Looking past TROPOMI, multi-
satellite approaches are emerging. For ex-
ample, by combining TROPOMI data with
high-resolution satellites that are designed
to track facility-scale emissions, scientists
can now precisely determine the source lo-
cations and quantify emissions, such as dur-
i n g a r e c e n t b l o w - o u t e v e n t at t h e Fo r d E a g l e
Shale regions in Texas, where nearly 5000
tonnes of methane were emitted in only 20
days because of a control loss at a gas well
( 12 ). The global capacity for satellite-based
monitoring of atmospheric methane should
increase in the coming years, with a whole
fleet of satellites waiting to join the hunt for
methane sources.
The next generation of satellites is ex-
pected to have better spatial and temporal
coverage, as well as improved resolutions and
accuracies. However, many of the planned
satellites may still struggle with measure-
ments performed over water, through clouds,
or at nighttime. They may also have shorter
operational periods than ground-based net-
works. These satellites could struggle to track
intermittent emitters with emissions under
their detection threshold. Thus, it is impor-
tant to integrate these satellite-based projects
with drone-based and ground-based methods
when tracking and quantifying emissions at
the regional scale.
Any future global methane monitoring
system, such as the International Methane
Observatory (IMEO) of the UN Environment
Programme and the European Commission
( 13 ), will have to combine observations across
different scales and techniques to be truly
comprehensive. As a first step, the differ-
ent methods and algorithms will have to be
standardized or at least be made compatible.
For example, a measurement of kilograms
of methane emission per hour at a specific
site by satellite A should be reproducible us-
ing data collected by satellite B or by a drone
at the same site. Such harmonization efforts
and the collation of best practices for atmo-
spheric monitoring are currently being ad-
vanced by the Integrated Global Greenhouse
Gas Information System (IG^3 IS) of the World
Meteorological Organization ( 14 ). These on-
going projects will continue to provide data to
scientists, site operators, policy-makers, and
citizens, to spur future research, help iden-
tify operational issues, develop cost-efficient
mitigation strategies. They will also help to
inform the public of where the planet is head-
ing in the grand scheme of climate change
and how successful the Paris Agreement and
the increased ambitions announced at the
COP26 in Glasgow are going to be. jREFERENCES AND NOTES- UN Environment Programme, Emissions
Gap Report 2021, http://www.unep.org/resources/
emissions-gap-report-2021. - T. Lauvaux et al., Science 375 , 557 (2022).
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(2019). - E. G. Nisbet et al., Rev. Geophys. 58 , 1 (2020).
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- UN Environment Programme, International Methane
Emissions Observatory, http://www.unep.org/explore-topics/
energy/what-we-do/methane. - Integrated Global Greenhouse Gas Information System,
(IG^3 IS), https://ig3is.wmo.int/.
10.1126/science.abm1676Some oil and gas facilities, such as this refinery in
Belarus, were identified as global methane emission
hotspots by latest satellite data analysis.
MOLECULAR BIOLOGYTethering gene
regulation to
chromatin
organization
A two-tiered system of
chromatin structure ensures
robust gene expression
By M arissa Gaskill and Melissa HarrisonP
recise regulation of gene expression
is crucial to cellular identity, and
changes to gene expression profiles
drive developmental transitions.
Distinct enhancer elements interact
with promoters to control cell type–
specific gene expression. These enhancers
are often located at a considerable distance
from the genes they regulate. Chromosome
looping and three-dimensional (3D) ge-
nome organization have been suggested to
bring the correct enhancers and promot-
ers together to facilitate the exquisite spa-
tiotemporal gene regulation required for
successful development. Nonetheless, it
remains unclear how genome organization
is precisely regulated to ensure that distant
enhancers locate the correct promoter to
reliably drive gene expression. On page 566
of this issue, Batut et al. ( 1 ) define a distinct
class of cis-regulatory elements called teth-
ering elements that promote interactions
between enhancers and promoters. They
propose a two-tiered system of genome or-
ganization: tethering elements that connect
distant enhancers to promoters and bound-
ary elements that ensure the specificity of
these enhancer-promoter interactions.
Within the nucleus, chromosomes are or-
ganized at multiple levels, including loops,
topologically associating domains (TADs),
and compartments. Investigations of the
role of chromatin structure have largely
focused on TADs, which are chromosomal
regions enriched for self-interaction and
delimited by insulator sequence elements.
Despite TADs being a conserved feature
of the eukaryotic genome, the importance
of this 3D structure to gene regulation re-Department of Biomolecular Chemistry, School of
Medicine and Public Health, University of Wisconsin-
Madison, Madison, WI, USA. Email: [email protected]4 FEBRUARY 2022 • VOL 375 ISSUE 6580 491