Hiatus in global mean temperature: trend patterns inspected with MSU/AMSU and GNSS-RO satellite data

Thursday, 18 December 2014
Johannes K Nielsen, Bo Christiansen, Hans Gleisner and Peter Thejll, Danish Meteorological Inst., Copenhagen, Denmark
Over the last 15 years, global mean surface temperatures exhibit only a weak trend - widely referred to as a hiatus - compared to the preceding 25-year period. Recent studies have attempted to attribute the hiatus to several causes, e.g., ocean-atmosphere energy exchange mechanisms, stratospheric water vapour, and impacts of volcanic emissions unaccounted for. Recently, the phenomenon has also been analysed in terms of incomplete sampling of the rapidly warming Arctic region.
We here examine zonal mean temperature trends in satellite-based tropospheric data sets with a global coverage, and compare them to the HadCRUT4 surface data set. MSU/AMSU data allow us to study tropospheric temperature trend patterns in the pre-hiatus period 1985--1997 relative to the hiatus period 2001--2013. The latter period is also covered by GNSS Radio Occultation (GNSS-RO) measurements from which geopotential heights of isobaric surfaces, and hence mean tropospheric temperatures, can be derived. Omission of successively larger polar regions from the global-mean temperature calculations, in both tropospheric and surface data sets, shows that data gaps at high latitudes can not explain the observed differences between the hiatus and the pre-hiatus period. Leaving out high latitudes leads to an under-estimation of the trend in the global means, but this effect is only a minor contributor to the hiatus phenomenon.Instead, the dominating causes appears to be found at low- and mid-latitudes.