The Challenge:
Methane is around 30 times more potent than carbon dioxide as a greenhouse gas. However, observations of methane at high latitudes are limited in comparison to those at low and mid-latitudes.
Coverage by ground-based and aircraft instruments is limited to specific locations and times and satellite measurements of methane at short wavelengths require sunlight which is not available in polar winter. This leaves scientists with incomplete information on methane at high latitudes with which to assess models and a gap in our understanding of methane links with climate change..
The Solution:
Scientists at RAL Space have developed a multi-year dataset using measurements from the Infrared Atmospheric Sounding Interferometer (IASI) on board EUMETSAT’s MetOp satellite. IASI provides coverage every 12 hours, day and night, at all latitudes in all seasons. This complements data-sets produced from short-wave satellite measurements by other
National Centre for Earth Observation (NCEO) and European groups.
The Outcome:
This dataset shows tropospheric methane to be increasing at all latitudes including the Arctic. Analysis should help establish the causes of increase in different regions eg whether the Arctic increase is entirely due to transport of methane from lower latitude sources (wetlands, wildfires, agriculture, industry) or possibly also to thawing permafrost. This could improve our understanding of the relationships between methane and climate change..
Brian Kerridge, Remote Sensing Group Leader, RAL Space said:
“IASI measurements from MetOp are currently providing a continuous, stable data record which commenced in 2007 and is due to be extended by MetOp Second Generation for a further two decades. Along with geographical and temporal coverage extending to polar regions in all seasons, our methane scheme resolves two vertical layers to help differentiate changes occurring lower in the troposphere from those occurring higher in the troposphere and stratosphere above.”
Next steps:
- RAL Space Remote-Sensing Group will be working with other NCEO groups to analyse the MetOp methane time-series.
- The Group is currently working with colleagues in the Netherlands and Germany to exploit the complementary vertical sensitivities of thermal infrared (IASI) and solar shortwave (Sentinel-5 Precursor TROPOMI) measurements. By combining information from the two wavelengths, the aim is to resolve methane in the near-surface layer and help improve estimation of surface fluxes around the globe.
- Combined wavelength retrieval has been demonstrated in the project for carbon monoxide but will be much more challenging for methane due to its variability being so much lower (typically ≤ 1% vs 10’s %) so the required accuracy being correspondingly higher.
Further background:
The RAL Space remote sensing group is one of the partners of NCEO.
Research was funded through the Natural Environment Research Council.
