Contribution of near-infrared bands of greenhouse gases to radiative forcing

The most important driver of climate change due to human activity is changes in concentrations of the greenhouse gases such as carbon dioxide and methane. The classic description of the greenhouse effects is that gases exert their influence on climate by altering fluxes of thermal infrared radiation (wavelengths 4 to 500 microns) emitted and absorbed by the Earth’s surface and atmosphere. These gases also absorb incoming radiation from the sun and in particular at near-infrared (NIR) wavelengths (0.7 to 4 microns). Until now, most studies have included NIR absorption by CO2 and water vapour, but have paid less attention to other gases.

This project focuses on methane which possesses a number of NIR absorption bands which are narrow regions of intense absorption, determined by the molecule’s structure, and vary in strength across the NIR. Methane concentrations have doubled over the past century and could double again by 2100. After CO¬2, methane is the second-most important contributor to climate change due to human activity.

Several studies indicate that methane’s NIR bands may be important but the contribution has not been quantified in detail. In particular, the impact depends on other atmospheric properties, such as clouds and water vapour, which vary strongly with altitude, latitude and season.

The project is based around numerical modeling of atmospheric radiative fluxes to achieve the most detailed description of methane’s NIR effect to date. It includes components which exploit existing observations including a major update to the main spectroscopic database used within atmospheric sciences, performing comparisons of simulations with measurements, and uses satellite retrievals of methane’s distribution. A number of alternative research avenues are possible for the latter part of the project, depending on student’s preferences. These could include considering NIR absorption of other molecules, or examining the response of the atmosphere to changes in methane concentration in more detail.

The student will gain detailed knowledge in atmospheric radiative transfer, as well as aspects of molecular spectroscopy. The student will also gain understanding of the main drivers of climate change, and the methodologies used to quantify their effect. The student will develop broader skills in numerical modelling, scientific computing and the handling and analysis of large datasets, and will have many opportunities to present their work to different audiences.

The project is supervised by Keith Shine (University of Reading), and co-supervised by Christine Chiu (University of Reading).

The full project description is available at: http://www.met.reading.ac.uk/nercdtp/home/available/desc/SC201609.pdf

A video is also available at https://youtu.be/roHM5liGmyA