Upper tropospheric humidity and climate change

The tiny quantities of water vapour in the air many kilometres above our heads is of central importance to the
Earth's greenhouse effect and ongoing climate change. It regulates the planet's natural cooling system through
absorption of outgoing infrared radiation and where the humidity exceeds saturation point determines the
distribution and thickness of high altitude clouds. Upper tropospheric humidity is an essential climate variable
because it controls key atmospheric processes, including water vapour and cloud feedbacks that can amplify the
climate system's response to increases in other greenhouse gases such as carbon dioxide. It is therefore vital to
understand past variability and change in upper tropospheric humidity and evaluate these key processes in
complex climate prediction models.

This project will exploit state of the art global satellite measurements and novel diagnostic tools to evaluate
dataset quality, quantify the variability of atmospheric humidity in space and time and use this information to
advance understanding of important atmospheric processes as well interrogate and improve detailed weather and
climate prediction models that are of great benefit to society. The research will provide a valuable interface
between Earth Observation and climate modelling, as well elucidating feedbacks processes fundamental to
climate change and therefore of great relevance to policymakers. The supervision team provides a broad
expertise across climate science and Earth Observation and there will be the opportunity to work with scientists
from the UK Met Office involved in the development of weather and climate models and with scientists
stationed in EUMETSAT who are directly involved in producing and extending key satellite observing systems.

The project will tackle some important questions including:
- How much does upper tropospheric humidity amplify climate change?
- Can state of the art climate models capture the processes determining variability and change in upper
tropospheric humidity?
- Will signatures from upper tropospheric humidity provide new insight into high altitude cloud feedbacks?
- How does upper tropospheric humidity control Earth's radiative energy balance and is there a tropical super
greenhouse effect?

The project will exploit existing data, numerical models and diagnostic tools and advance these systems to better interface Earth Observation and climate modelling as well as developing concepts relating to feedbacks processes that are fundamental for policy relevant quantitative climate science as listed below:
- Exploitation of new satellite measurements of UTH.
- Development of techniques to simulate consistent upper tropospheric humidity diagnostics in current climate models using existing software available from partners
- How can upper tropospheric humidity measurements by combined synergistically with Earth radiation budget and water cycle measurements

There will be opportunities to liaise and learn from EUMETSAT partners involved in developing Upper
Tropospheric Humidity datasets, the ESA Water Vapour Climate Change Initiative and the Met Office partners
on using and evaluating climate model simulations. This will provide comprehensive training in cross-disciplinary data analysis skills applied to models and Earth observations.