concerned with atmospheric conditions over land, sea, and ice and include such variables as temperature, wind speed and direction, pressure, cloud properties, and carbon dioxide levels. Ocean ECVs include sea surface and subsurface temperature and salinity, ocean color, sea ice, sea level, oxygen, and nutrients. Most terrestrial observations focus on ground water, water use, snow cover, land cover, and soil moisture.
The ECVs represent a consensus on a broad and comprehensive set of parameters to document Earth’s climate system. Designed primarily to characterize key aspects of the Earth system, they are aimed more at informing scientific analysis more than policy decisions. There have, however, been several attempts to develop indices based on the ECVs that would yield an integrated measure of climate impacts that could be more useful for policy analysis. One such index is the U.S. Climate Extremes Index (CEI). It was developed as a “monitoring and communications tool to help U.S. citizens and policymakers identify possible trends or long-term variations in a variety of climate extremes indicators” (Gleason et al., 2008). The CEI is composed of five parameters: monthly minimum and maximum temperatures, daily precipitation, days with and without precipitation, and the Palmer Drought Severity Index (PDSI) (Palmer, 1965). Temperature is important for monitoring a variety of phenomena, including heat waves, cold waves (including freeze events such as late spring freezes), and even unusually warm or cold months and seasons that can have effects on a variety of sectors. Precipitation is the basic building block for monitoring precipitation deficits and excess, including drought and heavy rain events. Air pressure is important for monitoring storms, heat waves, and other events, while water vapor is important for monitoring the potential for heavy rain events and drought. The PDSI is a dryness indicator based on a combination of recent temperature and soil moisture observations.
The CEI was tailored for the continental United States. Currently there is an effort to develop a CEI that would provide a more globally integrated picture of the current state of climate extremes. However, the development of such a global CEI has been hampered by a lack of data availability in many regions and for most of the ECVs. A white paper prepared for the 2011 World Climate Research Programme Open Science Conference (Trenberth et al., 2012) concluded that although the data for ocean and atmospheric ECVs have adequate global coverage over a long enough time and sufficient quality, data for terrestrial measurements are seriously deficient. It also concluded that although existing in-situ data cover most of the high-priority regions, spatial and temporal coverage could be improved. It called for more integration of satellite data as well as for new observations that would provide information about such areas as climate change mitigation and adaptation efforts. Data at regional and local scales on such factors as soil moisture, stream flow, and sea surface temperature