1. temperature trends in ipcc 20 th century runs v. radiosondes 2. volcanic signals
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1. Temperature trends in IPCC 20 th century runs v. radiosondes 2. Volcanic signals 3. Effects of volcanic eruptions on trends? Melissa Free John Lanzante. 6 models from 4 modeling centers: # runs Geophysical Fluid Dynamics LabGFDL2.03 GFDL2.13 - PowerPoint PPT PresentationTRANSCRIPT
1. Temperature trends in IPCC 20th century runs v. radiosondes
2. Volcanic signals
3. Effects of volcanic eruptions on trends?
Melissa Free John Lanzante
6 models from 4 modeling centers:# runs
Geophysical Fluid Dynamics Lab GFDL2.0 3GFDL2.1 3
Goddard Institute for Space Studies GISS ER* 9GISS EH* 5
Hadley Centre HadGEM 1
NCAR PCM 4
Simulations starting in 19th century, all forced with solar, volcanic, ozone, greenhouse gas changes and direct sulfate effects. (Models differ on details and some include other forcings.)* ozone forcing was wrong
K
50 mb T, 20N-20S
K
Models subsampled for RATPAC
Subsampled for RATPAC and HADAT- Differences largest in SHX
Quantifying the comparison
• Correlations between vertical profiles of trends, model v. observations (100-30 mb)
• Differences between stratospheric mean trends
• Compare results for adjusted and unadjusted data
• Tropical stratosphere—• Sonde data agrees with GFDL models for 1960-1999, but is too cool for 1979-1999.
• Differences are larger at 100 mb than above.
• PCM has different shape than data for extratropics (79-99)
• Homogeneity adjustments generally improve model-data trend agreement.
RATPAC observations Mean of models
Pinatubo zonal mean response
QBO and ENSO removed from data, ENSO removed from models.Mean of 24 months after minus mean of 24 months before.
K K
Volcanic effect, 30N-30SENSO and QBO removed
NH Extratropics Volcanic signal
SH ExtratropicsVolcanic signal, SH extratropics
K/decade
(RATPAC)
Effect of eruptions on temperature trends
Method based on Santer et al. (2001)1. Find lowest temperature within 24 months after eruption.2. Construct volcanic signal assuming linear ramp down to minimum,
followed by exponential decay3. Remove this signal from time series4. Find difference in trends
1979-2005Trend = - 0.16 K/dec
Models tend to overestimate stratospheric warming, especially after Pinatubo—especially PCM.
Biggest differences are at 100 mb for Pinatubo.
Dropping 2 years after eruptions is not an accurate method to estimate effects on trends.
Santer method also has large uncertainties.
Preliminary results suggest effects of eruptions on stratospheric trends are order 0.15 K/decade or less, small in comparison to the trends (work is still in progress).