ICE-IMPACT: International Consortium for the Exploitation of Infrared Measurements of PolAr ClimaTe

The Far infra red (FIR) is defined as the region of electromagnetic spectrum found at wavelengths greater than 15 microns. FIR radiation plays a major role in the Earth's energy balance, accounting for approximately half of the emission to space from the Earth and its atmosphere in the global mean. Fundamental physics implies that FIR radiation will play an even more important role in influencing climate variability and change in the fragile polar regions. The very cold surface temperatures found in these locations means that a greater fraction of the emitted surface energy is found at longer wavelengths. Moreover, the associated very low water vapour concentrations typically found in polar regimes effectively open up 'windows' in the FIR, making it possible to see further into the atmosphere from the ground than would normally be possible at these wavelengths. By the same argument, more of the surface energy emitted at these wavelengths is able to escape to space.

Recent work has suggested that assumptions about FIR surface characteristics made in many of the most advanced models that we use to predict climate - termed Earth-system models - mean that they may be missing an important polar climate feedback process. This could lead to an additional Arctic surface warming of up to 2 K by the 2030s which would be expected to affect the rate of ice-melt and sea-level rise. Termed the 'ice-emissivity' feedback, the mechanism depends on the fact that snow and ice emit more energy at FIR wavelengths than sea-water at the same temperature. Current Earth-system models typically assume that all surfaces have the same emissivity in the FIR and so do not include this feedback process. These same models also struggle to match surface observations of the downwelling radiation emitted by the atmosphere in polar regions, a shortcoming that is believed to be principally due to inadequacies in the representation of polar clouds. However, up to now a detailed evaluation of the polar radiation budget has been hampered by a lack of dedicated observations spanning the entire infrared, including the FIR.

This project seeks to address this deficiency by bringing together a team of international experts in FIR research and climate modelling to develop a suite of observationally based tools which will be used to assess model performance and drive future improvements. In the course of this work we will derive the first ever assessment of FIR surface emissivity from in-situ airborne observations over the Greenland plateau; characterise the infrared surface radiation budget over Antarctica and assess the meteorological processes driving variability there over a range of time-scales; evaluate approaches used to derive synthetic FIR measurements from space-based observations; and begin the process of quantifying the ice-emissivity feedback in two leading Earth-system models.

In the short-term the most obvious socio-economic benefit is an improved predictive ability for the UK in the polar regions, incorporating a physical mechanism, the 'ice-emissivity' feedback, that is missing in the current version of UKESM. This mechanism has been shown to have the potential to significantly increase the rate of temperature change in the Arctic and hence has important implications for both the region itself and further afield. Enhanced temperatures would be expected to result in accelerated ice-melt, with consequences for the rate of sea-level rise. They may also encourage permafrost melt and associated methane release, creating a further, positive feedback loop. Through the course of this project we will engage the wider, international modelling community, first via our project partners and then through a dedicated project workshop (W2 - see case for support/Pathways to Impact), in order that this benefit is translated beyond the immediate ICE-IMPACT team. Obvious links can also be made with proposed cross-centre NERC projects focused on UKESM and the North Atlantic Climate System, both of which have NCEO involvement.

Looking longer-term, a better, quantitative understanding of the importance of the ice-emissivity feedback mechanism will benefit both the indigenous population of the Arctic and those regions that may be affected by Arctic change, including the UK. It will directly impact planning decisions made by the relevant national agencies (e.g. DEFRA) relating to sea-level rise (e.g. coastal flood defences) and governmental/inter-governmental policy concerning 'safe' levels of anthropogenic greenhouse gas emissions. There are also clear benefits to improved predictive ability for the insurance industry and for those that might seek to exploit a permanent reduction in Arctic sea-ice (e.g. shipping industry, fishing industry, oil/gas exploration).

Turning to alternative aspects of the proposal, establishing the importance of far infrared radiation (FIR) in terms of both its contribution to polar climate and the unique information contained in this part of the spectrum should strengthen the case for a greater number of dedicated FIR measurements, whether that be from the ground, aircraft, balloon or satellite. For example, there have been recent advances in instrumentation, particularly detector technology, that make a satellite based FIR instrument more feasible than has been the case in the past. UK firms (e.g. Selex UK) are at the forefront of some of these developments and hence the efforts of the ICE-IMPACT team in this area has the potential to benefit both UK industry and science.

More generally, clearly the work will benefit the general public. This will occur through the provision of enhanced information to those making decisions which will impact resilience to change as outlined above, but can also be realised via improved education regarding the fundamental science we will perform. An understanding of the complexity of the climate system, coupled with honest reporting of areas of current uncertainty can lead to improved decision making at the individual level. It can also motivate the climate scientists of the future.