Scientists discover global warming linked to increase in tropopause height over past two decades

Space Daily ^ | January 5, 2003

[cogitator]

Scientists discover global warming linked to increase in tropopause height over past two decades

LIVERMORE, Calif. -- Researchers at the Lawrence Livermore National Laboratory have discovered another fingerprint of human effects on global climate.

Recent research has shown that increases in the height of the tropopause over the past two decades are directly linked to ozone depletion and increased greenhouse gases.

The tropopause is the transition zone between the lowest layer of the atmosphere -- the turbulently-mixed troposphere -- and the more stable stratosphere. The tropopause lies roughly 10 miles above the Earth's surface at the equator and five miles above the poles. To date, no scientist has examined whether observed changes in tropopause height are in accord with projections from climate model greenhouse warming experiments.

The comparison was made by Livermore scientists Benjamin Santer, James Boyle, Krishna AchutaRao, Charles Doutriaux and Karl Taylor, along with researchers from the National Center for Atmospheric Research, NASA Goddard Institute for Space Studies, the Max-Planck Institute for Meteorology and the Institut for Physik der Atmosphere in Germany. Their findings are reported in the today's (Jan. 3) online edition of the Journal of Geophysical Research-Atmospheres.

This research undercuts claims by greenhouse skeptics that no warming has occurred during the last two decades. Such claims are based on satellite measurements of temperatures in the troposphere, which show little or no warming since the beginning of the satellite record in 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," Santer said. "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. Tropopause height changes give us independent evidence of the reality of recent warming of the troposphere."

The Livermore research supports the bottom-line conclusion of the 2001 Intergovernmental Panel on Climate Change (IPCC), which states that, "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations."

Earlier research showed that changes in the Earth's surface temperature, ocean heat content, and Northern Hemisphere sea ice cover are other indicators of human effects on climate change.

"The climate system is telling us a consistent story -- that humans have had a significant effect on it," Santer said. "We're seeing detailed correspondence between computer climate models and observations, and this correspondence is in a number of different climate variables. Tropopause height is the latest piece of the climate-change puzzle."

To support the research, Livermore scientists examined tropopause height changes in climate-change experiments using two different computer climate models. Both models showed similar decadal-scale increases in the tropopause height in response to changes in human-caused climate forcings. The patterns of tropopause height change were similar in models and so-called 'reanalysis' products (a combination of actual observations and results from a weather forecast model).

The model experiments focused on both manmade climate forcings, such as changes in well-mixed greenhouse gases, stratospheric and tropospheric ozone, and on natural forcings, such as changes in volcanic aerosols. The forces have varying effects on atmospheric temperature, that in turn affect tropopause height, the report concludes.

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.

[rustbucket]

Contrast the steadily upward trend in CO2 concentration of your post 53 with the correlation between solar activity and global temperature of Friis-Christensen, E., and K. Lassen, "Length of the solar cycle: An indicator of solar activity closely associated with climate," Science, 254, 698-700, 1991.

This correlation of the length of the solar cycle does a much better job of explaining the up and down observed global temperature than the steadily increasing CO2 concentration. (Pardon the Danish, or whatever language the chart contains.)

I've heard that the Friis-Christensen/Lassen correlation did not perform as well over the last 10 years or so as it did before 1991. The observed temperature curve went higher than the solar correlation during this recent period. On the other hand, that sort of mismatch (observed temperature > solar correlation) has happened before at the ends of pre-1860 up-cycles in global temperature (other authors have extended this solar correlation back centuries in time).

The length of the solar cycle is a good proxy for solar radiation but apparently not a perfect one.

[AEMILIUS PAULUS]

Good observation. The global warming crowd is politically motivated. However, with what end in view? Pure power with resultant control? Economic warfare?

[rustbucket]

Note the plot of post 61.