Researchers at the Lawrence Livermore National Laboratory established that an increase in the height of the tropopause – the transition zone between the lowest layer of the atmosphere and Earth’s stratosphere – over the past two decades is directly linked to ozone depletion and a rise in greenhouse gases. Computer models run by the laboratory linked both human and natural climate forcing, such as volcano emissions, with changes in tropopausic height.
The discovery, reported in the latest issue of the Journal of Geophysical Research-Atmospheres, contradicts previous studies suggesting that no warming is taking place. So far satellite measurements of temperatures in the lower atmosphere – the troposphere – show little or no warming since 1979.
“Weather balloons and weather forecast models show that there’s been a pronounced increase in the height of the global tropopause over the last two decades,” says Benjamin Santer of the Lawrence Laboratory. “Our best understanding is that this increase is due to two factors: warming of troposphere, which is caused by increasing greenhouse gases, and cooling of the stratosphere, which is mainly caused by depletion of stratospheric ozone.”
Earlier research has shown that changes in the Earth’s surface temperature, ocean heat content, and Northern Hemisphere sea ice cover are all indicators of human effects on climate change. “We’re seeing detailed correspondence between computer climate models and observations, and this correspondence is in a number of different climate variables,” continues Santer. “Tropopause height is the latest piece of the climate-change puzzle.”