Trends and variability in Temperature profiles taken from Lauder, New Zealand

Abstract

Satellite and radiosonde measurements have shown that in the last few decades, globally, mean stratospheric temperatures have decreased. Cooling of the stratosphere is predominantly driven by anthropogenic $CO_2$ emissions and by decreasing stratospheric ozone concentrations from the 1980's. In the last decade, the stratospheric temperature appears to flatten of. This is suspected to be due to regulations under the Montreal protocol, restricting the emissions of ozone depleting substances and thereby limiting the ozone component in stratospheric cooling. However, research regarding the quantification of the separate contributions of ozone and $CO_2$ to the cooling is limited. This report describes and analyses temperature profile time series taken by a Lidar instrument, situated in Lauder, New Zealand. It is shown that the Lauder observations contain temperature trends in the upper stratosphere, where increased $CO_2$ abundance contributes to -0.4 to -1.5 K/dec cooling. In the lower stratosphere, $CO_2$ component varies from -0.3 to + 0.4 K/dec. Changes in ozone column above Lauder are small, causing ozone to contribute to a trend of approximately +0.1 K/dec. Additionally, the observations were compared with other lidar and sonde measurements. Observations at higher latitudes predominantly show stronger temperature trends than the Lauder observations, varying from a 0.5 to almost 2 K/dec of $CO_2$ induced cooling. Ozone columns, which are shown to recover at rates of 2\% per decade induce a positive temperature trend of up to 0.2 to 0.6 K/dec. Finally, it is shown that models used in the Coupled Model Intercomparison Project 5 (CMIP5) give adequate simulations of temperature trends in the Stratosphere with respect to the observations.