An International Framework for Climate
Monitoring from Space
The Contribution of Essential Climate
Variables to Climate and Other GEOSS
Societal Benefit Areas
The role that satellites play in observing
Earth’s climate variability and change has
increased substantially in recent decades.
Significant progress has been made in
observing Earth in time and space which,
before the advent of satellites, was all but
impossible. Satellite observations allow us
to construct global views of variables that
characterise Earth’s land, oceans and
atmosphere, such as cloudiness, ice-sheet
extent, sea-surface temperature and
vegetation cover. With some satellite
observations now spanning more than 40
years, their potential for climate
monitoring purposes has become increasingly
evident. Yet, a robust international
framework to realise and sustain this
potential does not exist.
Figure 1. Conceptual architecture of the
Global Earth Observation System of
Systems.
(Click image to view full size)
Many satellite sensors, systems and policies
were either not designed for climate
purposes, or were not intended to operate
over the long time frames needed for climate
assessments. To support weather prediction,
many space agencies have instituted
contingency agreements to ensure continuous
access to observations. This is not yet the
case for climate applications. Further,
despite recent progress, data-sharing
policies and practices remain less robust
for climate data than for weather data.
Clearly, there are international, as well as
national, policy mandates or structures
regarding climate and climate change. In
1988, the Intergovernmental Panel on Climate
Change was established by the United Nations
Environment Programme and the World
Meteorological Organization. Its charter is
to review and provide recommendations to
governments regarding the state of knowledge
of climate change science, the risks
associated with human-induced climate
change, the social and economic impacts of
climate change and possible response
strategies. In 1992, the United Nations
Framework Convention on Climate Change – an
international environmental treaty – was
established to consider actions for reducing
global warming. Nationally, reports like the
United Kingdom’s 2006 Stern Review and the
United States’ 2007 Decadal Survey have also
contributed to an increased awareness among
policy makers of climate change and
monitoring.
The IPCC’s 2007 4th Assessment Report
underscores the urgent need for
climate-observing capabilities, and an
international architecture supporting them, to
monitor the global water cycle and the global
carbon cycle. Key private sector stakeholders
include major industries, such as insurance,
agriculture, energy and transportation, who
have increasingly called for authoritative
climate reference data upon which to base
investments and strategic plans. Climate data
are also required to better observe and
predict trends in climate extremes, such as
drought, floods, tropical cyclones and coastal
hazards. Improved knowledge in these areas
translates into lives saved and property
protected, improved economic resiliency,
improved security and well-being of the
public.
What Are Essential Climate Variables?
The Global Climate Observing System identified
a set of geophysical variable types, or
Essential Climate Variables, that are
associated with climate variation and change.
The ECVs, such as cloud properties, sea state
and snow cover, are grouped into three
categories: atmospheric, terrestrial and
oceanic.
An ECV typically encompasses several
geophysical variables that characterise it.
For example, the cloud properties ECV includes
descriptors of cloud type, height, thickness
and composition. If a climate signal exists in
measurements of these variables, it typically
is small but persists over long time periods
(seasonal, interannual, and decadal to
centennial). This stands in contrast to the
often large, but short-term, changes
associated with weather. Thus, to detect
trends unambiguously, climate data products
must meet more rigorous criteria than many
other applications. The US National Academies
term such products Climate Data Records
(CDRs), defined as time series of measurements
that are of sufficient length, consistency and
continuity to determine climate variability
and change.
Two categories of CDRs exist based on data
content: Fundamental Climate Data Records
(FCDRs) and Thematic Climate Data Records
(TCDRs). An FCDR denotes a consistently
calibrated sensor data record that describes
the energy observed in space. Because
instruments continuously degrade in orbit,
FCDRs typically require data from a succession
of sensors, including sensors of different
designs. Scientists create unified and
coherent FCDRs by scientifically adjusting for
sensor changes. A TCDR denotes a geophysical
variable, such as cloudiness or ice-sheet
extent, that is derived from an FCDR. It is
closely connected to the ECVs, but strictly
covers exactly one variable.
Figure 2. The wide range of sustained
applications that can be addressed using
Essential Climate Variables derived from a
suite of Climate Data Records.
What Constitutes a Climate Data
Record?
Climate monitoring principles, requirements
and guidelines for the creation of CDRs have
been formulated to increase awareness within
space agencies to the specific observational
and procedural needs for establishing a
successful climate monitoring approach. A
complete characterisation of Earth’s climate
systems requires observations of the ocean,
land, cryosphere and atmosphere and the
coupling between these systems.
Climate monitoring requires near-continuous
observations, references to a common standard,
over at least several decades and, ultimately,
to a century or more. This is why an efficient
climate monitoring architecture needs to be
formulated and sustained.
Earth’s climate changes slowly relative to the
period over which any individual satellite
lasts. Hence, monitoring the climate system is
difficult unless a whole-system view is taken.
Most current CDRs are based mainly on data
from satellite systems primarily built to
support short-term weather and environmental
prediction applications. These records are
often extended backward in time by combining
them with historic ground-based
in situ data, such as surface air
temperature measurements. Thus, past weather
and Earth observations, from both in situ and
space-based sensors, have left an enormous
legacy of data that provides the basis of our
current knowledge on climate variability and
change.
Nevertheless, many peculiarities associated
with the satellite data must be addressed to
meet climate requirements. Depending on the
sensor, these may include challenges in
instrument calibration, limited traceability
to standards, underdetermined error budgets
and changes in the observation time-of-day.
These issues can introduce artefacts into
long-term time series and require careful
attention to produce quality climate products.
Figure 3 illustrates how climate scientists
correct calibration drifts across three
different instruments (without correction)
into a consistent climate data record over the
long term (with correction).
Figure 3. Original time series of
reflected sunlight from the land surface
(without correction) are transformed into
Climate Data Records (with correction)
using stable ground targets.
In addition, weather observations do not
address all climate observing needs, e.g.,
the observation of greenhouse gas
variability has negligible importance for
weather but is critical for climate
monitoring. The same is true for many land
and ocean biosphere observations. GCOS has
developed Climate Monitoring Principles that
set out a general guideline to achieve
observations with the required quality. The
monitoring principles address key
satellite-specific operational issues. These
include the availability of high-quality
in situ data for calibration and
validation of the satellite instruments. The
most relevant and comprehensive set of CDR
requirements is provided in Systematic
Observation Requirements for Satellite-Based
Products for Climate, a supplement to the
GCOS Implementation Plan applicable to
climate change and long-term variability
monitoring. The GCOS requirements are given
for a subset of the ECV where the
feasibility of satellite measurements has
been demonstrated. Although this ECV subset
currently does not reflect all important
climate variables, it evolves with each
update of the GCOS supplement. Increasingly,
agencies as well as international
initiatives are adapting to these
requirements. In some cases, this has been
done in a coordinated manner through CEOS,
based on a specific request arising from
UNFCCC.
Additionally, the scientific community has
requirements that evolve around specific
thematic interests, such as changes in
weather extremes or the Greenland ice sheet,
that arise independent of mission planning
but can have a significant influence on
future mission planning. Such requirements
are slowly integrated into the GCOS
Implementation Plan and updates of the
Satellite Supplements. However, space
agencies need to consider the observing
needs of the community independently of the
GCOS process even when it is not in phase
with mission planning.
International Coordination Efforts to
Produce Climate Data Records
Although the field of climatology has ancient
roots, the mixture of global change with
climate has led to the emergence of the new
field of geophysics: climate and global
change. This field has only emerged in the
last 20 years or so, however it is time now to
review and capture the best business practices
that have evolved. One of the greatest
challenges in this effort stems from the large
number of disciplines involved, spanning the
wide range of geophysics, computer science and
information preservation. In order to move
forward, a ‘lingua franca’, or common language
or understanding, must be developed as the
challenge requires a concerted international
effort.
Space agencies have established steps,
procedures and guidelines for the evolution of
mature research data records into a sustaining
production context, based on recommendations
from expert bodies such as the US National
Academy of Sciences and GCOS.
Such practices are being described and
shared through coordination bodies such as
the Working Group on Climate within the
Committee on Earth Observing Satellites
(WGClimate CEOS). WGClimate leads the CEOS
effort to provide a coordination mechanism
amongst space agencies to use Earth
observations to monitor and understand
climate variability and change.
To ensure success, WGClimate is engaged in
defining a framework, known as an
architecture. In building structures, the
term ‘architecture’ refers to the process of
planning, designing and construction.
This term has been adopted by the
information technology community to refer to
the design of a system. In this case, it
applies to the information technology system
required for climate information
stewardship, consisting of data collection,
data quality, archiving, processing,
reprocessing, discovery and access for
climate data records.
A Vision for a Sustained Observation System
for Climate Monitoring from Space
This vision of a sustained observation system
for climate monitoring can be expressed by its
intended usage. To date, three main usage
scenarios have been identified:
- To promote a common understanding amongst
the various stakeholders for meeting the
various climate monitoring requirements;
- To assist in the assessment of the degree to
which the current and planned observing
systems meet the climate monitoring
requirements;
- To gain an appreciation of the information
flows and dependencies of the end-to-end
processes (i.e. from sensing right through to
decision-making).
Two graphical views can be used to describe
the architecture: a logical view describing
the required data flows and functions, and a
physical view describing the implementation
characteristics.
Figure 4. Logical view of a climate
architecture.
(Click image to view full size)
In this end-to-end logical view, the
information flow starts with the satellite
sensing of the Earth environment. The
resultant observations are then assembled,
processed and converted to climate records.
These records are then used by the relevant
applications to generate reports, which are,
in turn, used by decision-makers (including
policy-makers) to determine a course of
action. The observation system for climate
monitoring is limited to the first two
pillars and, as illustrated in the following
diagram for the second pillar, it is
possible to ‘drill down’ within each of the
pillars in order to expose their constituent
functions and data flows.
Whilst the logical view is generic in that
it applies to all ECVs, in order to
facilitate the assessment of the
implementation status for each ECV, the
physical view has an ECV-specific focus and
typically consists of three types of
information:
• ECV-specific Requirements;
• Current Implementation Status for each
ECV;
• Planned (but not yet implemented)
Contributions for each ECV.
Thus, the physical architecture will allow
CEOS Agencies to coordinate their climate
observation, processing, archival and access
functions to ensure they meet societal
requirements.
in 2014, the database of ECVs will be
integrated with the CEOS Database of
Missions, Instruments and Measurements.
The ESA Climate Change Initiative:
Satellite Data Records for Essential
Climate Variables
The Climate Change Initiative (CCI)
was set up by the European Space
Agency as a response to the UNFCCC’s
need for systematic observations and
data archive development related to
improving understanding of the
climate system. The principal
objective of the programme is to
realise the full potential of the
long-term global Earth observation
archives that ESA has established
over the last 30 years, as a
significant contribution to the
Essential Climate Variable databases
required by GCOS.
It will therefore contribute to the
international CEOS response to the
Global Climate Observing System and
is expected to underpin the
establishment of a climate service
under the European Global Monitoring
for Environment and Security
initiative.
CCI complements existing efforts in
Europe (e.g., those led by EUMETSAT)
and internationally (e.g., under the
umbrella of SCOPE-CM). The success
of the programme will be measured by
the quality of its satellite-based
ECV products, the impact the
products have in the climate change
community (such as in the IPCC
reports) and its ability to
establish lasting and transparent
access to these results. CCI is
dedicated to the systematic
generation of fully described,
error-characterised and consistent
satellite-based ECV products.
Each ECV project team brings together
a diverse set of people from a range
of institutions, fronted by a science
leader. Each team is designed to
contain three groups of expertise, an
Earth observation group, a system
engineering group and a climate
research group. To ensure full
engagement with the climate modelling
community, an additional project was
established; the Climate Modelling
Users Group provides a forum for
feedback and discussion between
modellers and observation scientists.
This group is intended to ensure the
maximum utility of the products
produced by CCI.
— The lifetime of the programme is
divided into three phases; In the
first, innovative approaches for
continuous generation of ECVs are
being defined and validated, so the
products can be specified and
prototyped. The second phase will
develop the operational systems to be
put in place for ECV production,
bringing together the relevant science
communities with industry and data
centres in Europe. The final stage
will provide a framework for
comprehensive feedback from the
climate community and guidance on
future evolution of ECV production.
— Throughout the programme,
best-practice examples are followed,
all processes are well-documented and
made as transparent as possible and,
at all stages, time is allowed for
feedback, iterations and consultation
with a wider community of users and
experts.
— Cross-cutting activities across the
wide range of project topics provide
valuable, high-level discussions on
data standards and harmonisation, data
quality, data access, etc. The
programme also provides an opportunity
to exploit the benefits of
interdisciplinary teams to tackle new
science questions arising from the ECV
products and, thus, develop a
well-connected, Earth observation
science community.
Figure 5. A breakdown of the physical
architecture which allows CEOS agencies to
coordinate resources for addressing climate
and other societal benefit areas.
ESA's Climate Change Initiative has a
number of ECV projects in support of the
climate architecture.
