Global warming is now widely acknowledged based on a variety of direct measurements as well as remotely-sensed and proxy data. Its expression at the surface, which is most relevant to societal concerns, is primarily based on studies utilizing air temperature measurements over the land and bulk water temperature measurements over the oceans. Early ocean temperature measurements were made from ships but more recently have been supplemented with ocean temperatures derived from satellite measurements that have the advantage of providing near-global coverage. Similar satellite derived measurements of land surface temperature have not been incorporated into global warming studies since the emissivity of most land surfaces is not sufficiently well known to allow their temperature to be measured with the necessary accuracy and precision from satellite data. One land surface whose temperature can be accurately measured with satellite data is water since, as with the oceans, the emissivity of water is well known. Inland water body temperatures can be used to supplement and enhance traditional land air surface temperature measurements which have been shown to be susceptible to interference from land use / land cover changes (e.g., urbanization) and do not provide complete global coverage. Moreover, due to the greater precision, as well as the significantly smaller high-frequency variability, associated with satellite-derived values of inland water body surface temperatures, the detection and quantification of trends has the potential to be more robust than for surface air temperature data. In addition to their surface temperature, large inland water bodies also provide other important indicators of climate change since the timing of their thermal cycle is sensitive to climate (e.g., freeze-thaw).
The primary objectives of this work are (1) use satellite derived water surface temperatures to characterize the thermal behavior of the 50 largest inland water bodies in the world and 100 largest US water bodies for the last three decades; (2) relate changes in the thermal behavior of the water bodies to global and regional climate change as indicated by surface air temperature data; (3) identify changes in the secondary characteristics of the thermal behavior of inland water bodies that result from climate change as a possible predictors of future change, e.g., timing of freeze-thaw; (4) compare the regional trends in surface temperature climate derived from these observations to those depicted in the 20th Century IPCC climate simulations.
The results from this study will help NASA address the goal of its Earth Science Research Program to utilize global measurements to understand the Earth system and its interactions as steps toward the prediction of Earth system behavior. The work will produce a dataset which compliments existing air temperature data and will be used to study regional climate change. The dataset will be used in conjunction with climate simulations to provide insight into future regional climate change and its impact on large water bodies. Moreover, it will provide the means to better exploit the vast amount, and relatively long-record (~30 years), of satellite-derived thermal data over land regions for the purpose of detecting, quantifying and understanding climate change.
