Feasibility and Sensitivity Studies for CLARREO: A new opportunity for climate monitoring from space

The work we propose to undertake here will assist colleagues in the USA in the design of a new mission that will make extremely accurate observations of the Earth's climate from space, which can ultimately be used to improve our ability to predict (model) the future climate. The Earth's climate system represents a balance, when seen from space, between the incoming energy from our Sun (solar energy), which heats the Earth, and the outgoing infrared (IR) energy, the loss of which cools the Earth. Visible light is composed of many different colours, or wavelengths, and this is also true for the solar and IR energy. By making measurements of the relative amounts of energy at different wavelengths (spectral signatures or fingerprints), using a spectrometer, it is possible to determine the current state of the climate. Just as we have individual fingerprints, important climate variables have their own individual spectral signatures. Therefore, by measuring these spectral signatures at different times and comparing them, it is possible to understand how the climate has changed over that time period. Current spectrometers do exist, but have limitations in terms of their accuracy or sampling. It is intended that the new mission proposed here will sample the entire Earth with sufficient accuracy for the first time for the measurements to be used as a rigorous test of the ability of our current climate models to represent the current climate, and hence better predict future changes. Resources are limited, so it is essential that we specify exactly how these measurements are made. The most important points to consider are the accuracy of the measurements, the time between making measurements over the same area of the Earth, and how detailed these measurements are. The series of studies we propose here will enable us to determine the minimum requirements of the measurements that will be needed to achieve the goal of detecting decadal scale climate change, and attributing the changes seen to specific causes. These studies will enable us to advise our NASA colleagues as to the composition of the mission, in terms of the number of satellites required, the frequency and detail (spectral resolution) of the measurements made and the accuracies required. In addition, we also propose to build a UK CLARREO Project Team of interested UK parties to facilitate greater involvement in the US-led project across the UK as a whole.