{ntergovernmental Oceanographic Commission of the United Nations Educational, Scientific and 
Cultural Organization (IOC-UNESCO), the United Nations Environment Programme (UNEP), 
and the International Science Council (ISC). GCOS regularly reviews the status of the required 
monitoring system and produces guidance for its improvement. Status and guidance are given 
in documents including the Adequacy Reports (in 1998, 2003), Implementation Plans (in 2004, 
2010, 2016), and Progress Reports (in 2009, 2015, 2021). At the time of writing, the current 
[mplementation Plan is from 2016 (GCOS 2016) and a new one is in preparation for release in 
2022. GCOS reports to the United Nations Framework Convention on Climate Change (UNFCCC) 
in Workstream “Systematic Observations” and regularly reports to the Subsidiary Body for 
Scientific and Technological Advice (SBSTA). GCOS is directly involved in the process of the 
!JNFCCC and Conference of the Parties (COP; https://gcos.wmo.int/en/about/UNFCCC). 
One of the key concepts introduced and promoted by GCOS is that of Essential Climate Vari- 
ables (ECVs; Bojinski et al. 2014). An ECV is a physical, chemical or biological variable—or group 
’f linked variables—that critically contributes to the characterization of the Earth’s climate. 
Notably, ECVs need to be relevant (as a matter of fact, essential), feasible, and cost effective to 
monitor. They must make a critical impact as a UNFCCC Systematic Observation (essential and 
relevant), be measurable globally with existing technologies (feasible), and at an affordable 
level of investment (cost effective). GCOS currently defines 54 ECVs (https://gcos.wmo.int/en/ 
assential-climate-variables). GCOS ECVs come with requirements, guidance, and best practices for 
the generation of high-quality Climate Data Records (CDRs). The GCOS requirements are data 
characteristics that must be met by CDRs (in terms of spatial and temporal resolution, accuracy, 
stability, etc.) to ensure their fitness for purpose. Funding and implementation agencies external 
to GCOS use the ECVs and their requirements as targets for their research and development and 
aperational monitoring activities, The interplay between the GCOS ECVs and the implementation 
agencies is paramount to the development and sustainability of the global observing system. 
The ECV Inventory (https://climatemonitoring.info/ecvinventory/), maintained by space agencies, 
holds information on existing and planned satellite-based CDRs addressing the ECVs. 
GCOS has at present one ECV, the sea ice ECV, to encapsulate all aspects of the sea ice envi- 
ronment. This ECV is under the umbrella of the Ocean Observations Physics and Climate Panel 
(OOPC), which is responsible for maintaining and evolving the definitions and requirements of 
all 19 Ocean ECVs. Linked to the Ocean ECVs are the Global Ocean Observing System (GOOS) 
Essential Ocean Variables (EOV; see www.goosocean.0rg/eov). The EOV concept was introduced 
in the Framework for Ocean Observing (Lindstrom et al. 2012) and covers not only climate but 
also ocean health and operational oceanography aspects. GOOS is the designated steward for 
3COS Ocean ECVs, including sea ice. Since July 2020, the Global Cryosphere Watch (GCW), a 
body of WMO specialized in all aspects of the cryosphere, is a co-steward of the sea ice ECV. 
Sea ice is a key component of the climate system and a headline indicator of climate change. It 
is also a very multivariate environment with processes unfolding at a wide range of spatial and 
temporal scales. Long-term, stable, and error-Characterized CDRs of the sea ice environment are 
required for key applications such as monitoring climate change at global (Comiso et al. 2017b; 
Parkinson 2019; Trewin et al. 2021) and local scale (Cooley et al. 2020), evaluating climate simu- 
lations (Notz and SIMIP Community 2020; Roach et al. 2020; Davy and Outten 2020), providing 
input and boundary conditions to reanalyses (Hersbach et al. 2020; Lellouche et al. 2021), or 
:ombined model- and data-driven inference about future Arctic climate (Notz and Stroeve 2016). 
Because of the harshness and remoteness of the polar regions, sea ice CDRs rely mainly upon 
satellite Earth observation data, supported by a limited but indispensable set of in situ observa- 
tions (such as buoys, moorings, submarine and ship expeditions, and flight campaigns). 
Our main motivation for this contribution—a call for a revision of the current single-ECV 
model that suboptimally implements the multivariate sea ice environment—is backed up well by 
the communitv needs to improve the monitoring of polar regions for mitigation and adaptation 
AMERICAN METEOROLOGICAL SOCIETY ont 40 you by BEE SAMT FÜR SEESCHIFFAHRT | Unauthentit4NF; 88270615 9930/22 02:53 PM UTC