What determines the sensitivity of Earth’s climate to different greenhouse gases?
Dr Amanda Maycock, Dr Alex Rap, Dr Chris Smith, Prof Piers Forster
The perturbation to Earth’s energy balance from changes in atmospheric greenhouse gases can be quantified through the concept of radiative forcing. Since preindustrial times radiative forcing due to human activities has been positive and this has resulted in warming of the planet (IPCC, 2013). Key to this trend has been the positive radiative forcing from increases in carbon dioxide, methane and tropospheric ozone. Understanding radiative forcing trends is therefore vital for understanding Earth’s past and future climate.
Interestingly, changes in a given greenhouse gas imposed in different parts of the atmosphere do not have the same impact on radiative forcing. In particular, a change in greenhouse gas mixing ratio in the upper troposphere and lower stratosphere (between 300-100 hPa in pressure) induces a larger radiative forcing than the same change imposed in another region (see Figure 1). This is important because trends in some key greenhouse gases, such as ozone and water vapour, may be larger in the upper troposphere and lower stratosphere where they are potent greenhouse gases.
Figure 1: The impact of perturbations in (left) ozone, (centre) water vapour, (right) methane made at different latitudes and heights on radiative forcing. The figure shows that changes in these important greenhouse gases do not have the same impact on radiative forcing and climate depending on where the changes occur.
This REP project will give a student the opportunity to investigate the physical factors that determine how different greenhouse gases affect radiative forcing. In particular, we would like to answer:
- What properties of the atmosphere cause the sensitivity of radiative forcing from greenhouse gases to be larger in the upper troposphere and lower stratosphere?
- What factors cause the structure of radiative forcing sensitivity to be different for different greenhouse gases such as methane, carbon dioxide and ozone?
In addition to undertaking this research, the student will have the opportunity to attend the Royal Meteorological Society Student and Early Careers conference, to be held in Exeter on 11-12th July 2017, to meet other scientists and learn about a wider range of atmospheric and climate science topics.
The project would suit students with a background in Physics/Maths/Engineering who are interested in climate change and atmospheric physics. Some experience of scientific computing would be an advantage, but is not essential. You will be supported in running and analysing your own numerical simulations (using Fortran, IDL and/or Python). During the placement you will be a member of the Physical Climate Change group, a very active and supportive research group in ICAS.