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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 8C/decade) that are significantly larger than over the
ocean (0.06-0.12 8C/decade). Temperature trends in the mid-troposphere
of 0.08-0.11 degrees 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.