Abstract
Observed near-surface temperature trends during the period 1979–2014 show large differences between land and ocean, with positive values over land (0.25–0.27 °C/decade) that are significantly larger than over the ocean (0.06–0.12 °C/decade). Temperature trends in the mid-troposphere of 0.08-0.11 °C/decade, on the other hand, are similar for both land and ocean and agree closely with the ocean surface temperature trend. The lapse rate is consequently systematically larger over land than over the ocean and also shows a positive trend in most land areas. This is puzzling as a response to external warming, such as from increasing greenhouse gases, is broadly the same throughout the troposphere. The reduced tropospheric warming trend over land suggests a weaker vertical temperature coupling indicating that some of the processes in the planetary boundary layer such as inversions have a limited influence on the temperature of the free atmosphere. Alternatively, the temperature of the free atmosphere is influenced by advection of colder tropospheric air from the oceans. It is therefore suggested to use either the more robust tropospheric temperature or ocean surface temperature in studies of climate sensitivity. We also conclude that the European Centre for Medium-Range Weather Forecasts Reanalysis Interim can be used to obtain consistent temperature trends through the depth of the atmosphere, as they are consistent both with near-surface temperature trends and atmospheric temperature trends obtained from microwave sounding sensors.
Highlights
Records of global annual surface temperatures for the last 100 yr are an important data set often used in climate research, including the empirical assessment of climate sensitivity (Schwartz et al, 2014; Skeie et al, 2014; Lewis and Curry, 2015 and references therein)
We conclude that the European Centre for Medium-Range Weather Forecasts Reanalysis Interim can be used to obtain consistent temperature trends through the depth of the atmosphere, as they are consistent both with near-surface temperature trends and atmospheric temperature trends obtained from microwave sounding sensors
The results from GISTEMP and HadCRUT4 are practically identical despite the fact that they are computed from data with a different areal coverage
Summary
Records of global annual surface temperatures for the last 100 yr are an important data set often used in climate research, including the empirical assessment of climate sensitivity (Schwartz et al, 2014; Skeie et al, 2014; Lewis and Curry, 2015 and references therein). Global temperature records of the troposphere can only be used for limited time periods as data are only available globally with suitable accuracy since 1979 because of limited upper air observations from the Southern Hemisphere (SH) and the tropics before this date Radiosonde data on their own have not been considered, because except when controlled and integrated into data assimilation, these data are subject to significant network and instrumental changes (Thorne et al, 2011). For this reason, we do not intend to use observations from the free atmosphere directly but instead use re-analyses, though we will use temperatures derived from microwave sounders for comparison.
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