Essential Climate Variable (ECV)

An Essential Climate Variable (ECV) is a physical, chemical or biological variable or a group of linked variables that critically contributes to the characterization of Earth’ s climate. ECV datasets provide the empirical evidence needed to understand and predict the evolution of climate, to guide mitigation and adaptation measures, to assess risks and enable attribution of climate events to underlying causes and to underpin climate services. They support the work of United Nations Framework Convention on Climate Change (UNFCCC) and Inter-governmental Panel on Climate Change (IPCC).

GCOS

The Global Climate Observing System (GCOS) works towards a world where climate observations are accurate, sustained and access to climate data is free and open. It regularly assesses the status of global climate observations and produces guidance for its improvement. It is co-sponsored by the World Meteorological Organization (WMO), the Inter-governmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization (IOC-UNESCO), the United Nations Environment Program (UN Environment) and the International Science Council (ISC). GCOS expert panels maintain definitions of Essential Climate Variables (ECVs) which are required to systematically observe Earth`s changing climate.

GCOS currently specifies 54 ECVs under different categories & sub-categories as shown below. The expert panels regularly develop plans on how to sustain, coordinate and improve physical, chemical and biological observations. They identify gaps by comparing the existing climate observation system with these ECVs.

Atmosphere

Surface

Precipitation Pressure Radiation budget Temperature Water vapour Wind speed and direction

Upper-air

Earth radiation budget  Lightning Temperature Water vapor Wind speed and direction

Atmospheric Composition

Aerosols Carbon dioxide, methane and other greenhouse gases Clouds Ozone Precursors for aerosols and ozone

Land

Hydrosphere

Groundwater Lakes River discharge Terrestrial water storage

Cryosphere

Glaciers Ice sheets and ice shelves Permafrost Snow

Biosphere

Above-ground biomass Albedo Evaporation from land Fire Fraction of absorbed photosynthetically active radiation (FAPAR) Land cover Land surface temperature Leaf area index Soil carbon Soil moisture

Anthroposphere

Anthropogenic Greenhouse gas fluxes Anthropogenic water use

Ocean

Physical

Ocean surface heat flux Sea ice Sea level Sea state Sea surface currents Sea surface salinity Sea surface stress Sea surface temperature Subsurface currents Subsurface salinity Subsurface temperature

Biogeochemical

Inorganic carbon Nitrous oxide Nutrients Ocean colour Oxygen Transient tracers

Biological/ecosystems

Marine habitats Plankton