attribution of stratospheric temperature trends to forcings
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Attribution of Stratospheric Temperature Trends to Forcings. A coupled chemistry-climate model (CCM) study Richard S. Stolarski NASA GSFC In collaboration with Steven Pawson, Anne Douglass, Paul Newman, Mark Schoeberl and Eric Nielsen. - PowerPoint PPT PresentationTRANSCRIPT
Attribution of Stratospheric Temperature Trends to Forcings
A coupled chemistry-climate model (CCM) study
Richard S. Stolarski
NASA GSFC
In collaboration with Steven Pawson, Anne Douglass, Paul Newman, Mark Schoeberl and Eric Nielsen
SPARC Temperature Trends Meeting, Washington DC, April 12-13, 2007
Difference in Temperature between Past and Future Simulations
Past simulation used observed SSTs (1950-2005). Future simulation used model-generated SSTs (1996-2100). Overlap period was used to adjust future temperatures to make a consistent time series.
Contours indicate the latitude and altitude dependence of the adjustments. All temperatures used in this analysis are annual means.
Model Simulated Temperature Change 1979-1998 (K/decade)
Upper Stratospheric Cooling by Radiation to Space
Ozone HoleCooling
Dynamic Response to Ozone Hole
TroposphericWarming
Can we quantitatively separate the contributions of ozone change and greenhouse gases in our simulations?
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms:
Midlatitude Upper Stratosphere
We will fit this function with 4 terms:
Mean + a1•EESC + a2 •CO2 + a3 • CH4
Thin line: model output
Thick line: Fit with All Terms
CO2 Term (+mean)
EESC Term (+mean)
CH4 Term (+mean)
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms:
Midlatitude Upper Stratosphere
Fit uses entire 140-year simulation time series
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms:
Midlatitude Upper StratosphereThin line:
model output
Thick line: Fit with All Terms
CO2 Term (+mean)
EESC Term (+mean)
CH4 Term (+mean)
Change from 1979-1998
-1.9K EESC
-0.7K CO2
-0.4K CH4
-3.0K Total
Thin line: model output
Thick line: Fit with All Terms
CO2 Term (+mean)
EESC Term (+mean)
CH4 Term (+mean)
Change from 1979-1998
-1.9K EESC
-0.7K CO2
-0.4K CH4
-3.0K Total
Change from 2006-2025
+0.7K EESC
-1.3K CO2
-0.6K CH4
-1.2K Total
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms:
Midlatitude Upper Stratosphere
Relative Contribution of EESC, CO2, and CH4 to Temperature
Change at 1 hPa 40oN
1979-1998 2006-2025
Term Sens (K/ppbv) MR (ppbv) T (K) MR (ppbv) T (K)
EESC -9.2±0.3x10-1 +2.1x100 -1.9 -7.6x10-1 +0.7
CO2 -2.4±0.1x10-5 +2.9x104 -0.7 +5.5x104 -1.3
CH4 -2.0±0.2x10-3 +1.9x102 -0.4 +2.9x102 -0.6
Total -3.0 -1.2
How long must the record be to separate effects by
time-series analysis?
Effect of Length of Record on Fitting: Graphical Illustration: 40oN, 1hPa
Effect of Length of Record on Fitting: Graphical Illustration: 40oN, 1hPa
Continued
Sensitivity to EESC and CO2 as a Function of Endpoint of Output
40oN 1hPa
These are trends from 1979 through 1998 calculated from output from 1979 through various end years. Thin lines in left panels are 2.
Some Other Locations in the
Stratosphere
Northern Mid Latitude Lower Stratosphere
1979-1998 2006-2025
Term Sens (K/ppbv) MR (ppbv) T (K) MR (ppbv) T (K)
EESC -1.3±0.4x10-1 +2.1x100 -0.3 -7.6x10-1 +0.1
CO2 -3.0±0.4x10-6 +2.9x104 -0.09 +5.5x104 -0.16
CH4 -6.5±1.5x10-4 +1.9x102 -0.13 +2.9x102 -0.19
Total -0.5 -0.25
Methane term includes effects of increased HOx
60% EESC
Sensitivity to EESC and CO2 as a Function of Endpoint of Output
40oN 50hPa Statistically significant after 2020, but uncertainty never gets less than 50%
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms: Antarctic Lower Stratosphere
Thin line: model output
Thick line: Fit with All Terms
CO2 Term (+mean)
EESC Term (+mean)
CH4 Term (+mean)
Antarctic lower stratospheric temperature is dominated by ozone hole from ~1960 through 2100. Greenhouse gas terms are minor.
Fitting Model Temperature Time Series to EESC, CO2, and CH4 Terms: Antarctic Upper Stratosphere
Antarctic upper stratospheric temperature increases due to dynamic response to ozone hole through 2000. Thereafter, temperature decreases as ozone hole recovers and GHGs continue to cause decrease.
Map of EESC Term Using Output from 1979 to:
2010
2025 2040
2015 2020
2060
Color Regions are Statistically Significant
Greenhouse Gas (CO2) Term Using Output from 1979 to:
2010
2025 2040
2015 2020
2060
Some Tentative Conclusions
• Simulations indicate about 2/3 of annual temperature trend of upper stratosphere due to ozone decrease
• Simulations indicate about 60% of annual temperature trend of lower mid latitude stratosphere due to ozone decrease
• Upper stratospheric ozone effect should be able to be separated from greenhouse gas effect with present data: a few more years are needed to reduce uncertainties (of course this assumes a lot about the simulation’s representation of variability and its lack of QBO and solar cycle).