SURFACE TEMPERATURE OF THE GLOBAL OCEANS

We need to know more accurately how the surface temperature of Earth is changing, because of concerns about climate change. Since most of Earth is covered in water, ocean temperatures are a major component of global temperatures. But vast areas of ocean are rarely visited by shipping or buoys and are sparsely measured, so estimates of sea surface temperature (SST) from infrared sensors on satellites in space are essential to getting a global picture. Satellite SSTs, however, are prone to errors (biases) that mean they have not been stable enough to use to study decadal temperature trends. Since 1991, a series of sensors (the Along Track Scanning Radiometers, or 'ATSRs') have been flown on European satellites. These sensors have been more carefully calibrated and are more stable than any similar instruments. Over recent years, careful research has shown how to obtain SSTs from the ATSRs that we can be confident have biases less than about one tenth of a degree globally. Remarkably, this has been done by performing computer simulations of ATSR observations based on the physics of radiation and how it interacts with matter. This is useful, because it gives confidence that the ATSR SST estimates are valid globally, even in regions where there are few direct measurements available to check them against; this is in contrast to other satellite SSTs that are not independent of direct measurements. In this project, the observations from the ATSRs will be re-worked using new state-of-the-art techniques, which are aimed at minimizing errors, and, where errors remain, understanding those errors thoroughly. We expect the SSTs we finally obtain to be sufficiently stable, accurate and independent to be used for climate research. The new SST record we create will significantly improve our assessment of changes in data-sparse seas; and in regions where temperatures are measured by shipping, etc, the new satellite SSTs may even be able to give us insight into the errors in these direct measurements. We will create a new synthesis of all SST observations, including the new satellite SSTs. This will be used at the Hadley Centre to revise the best estimates of the global pattern and rate of climate change over recent decades, and to better attribute observed climate change to its causes. These results will be useful in various contexts. It will allow government policy to be formulated on the basis of better information about climate change, and will feed into intergovernmental assessments about climate change science. Marine surface temperatures are useful to the Royal Navy for planning operations, which can be anywhere in the world. The SSTs will be used by scientists looking at the transfer of heat and gases between the atmosphere and ocean. Ocean forecasting centres use measurements of SST by ships, etc, to keep their ocean model on track with reality, so better understanding of the errors in these inputs from this project will benefit ocean forecasting too.