# Presentation: 910939

## Attribution of observed climate trends over the United States during 1950-2000

- Hailan Wang12, Siegfried Schubert1, Max Suarez1, Junye Chen13, Martin Hoerling4, Arun Kumar5, Philip Pegion16
- 1NASA/GMAO; 2UMBC/GEST; 3UMD/ESSIC; 4NOAA/ESRL; 5NOAA/NCEP/CPC; 6SAIC

- NOAA 32nd Annual Climate Diagnostics and Prediction Workshop
- October 22-26, 2007

## Observed Seasonality and Regionality in Climate Trends over U.S.

**Observed Seasonality and Regionality in Climate Trends over U.S.**
- HadCRU; 1950-2000

**Surface Air Temperature (T)**

**Precip (P)**

**Notes:**
Definition of linear trends
Different processes affecting US during winter and summer

## Observed Seasonality and Regionality in Climate Trends over U.S.

**Observed Seasonality and Regionality in Climate Trends over U.S.**
- HadCRU; 1950-2000

- Black: US mean (235°E-285°E; 26°N-50°N)
- Gray: central US mean (250°E-275°E; 30°N-48°N)

**Distinct cooling and wetting trends during late summer and fall**

- 3-mon RunMean

- 3-mon RunMean

## Motivation

- Attribution of seasonality and regionality in observed climate trends over the U.S. during 1950-2000; specifically:
- To what extent do the leading SST patterns explain the observed seasonality and regionality of the surface air temperature and precipitation trends over the U.S. during 1950-2000?

## Model (AMIP) vs Obs

**HadCRU**

**NASA NSIPP AMIP EnsMean(14)**

**Model (AMIP) vs Obs**

**Notes:**
Time series of T and P for all four seasons: NSIPP AMIP vs HadCRU

## NASA NSIPP AMIP EnsMean vs HadCRU: Seasonality

**NSIPP AMIP **
**EnsMean**

**HadCRU**

**NASA NSIPP AMIP EnsMean vs HadCRU: *****Seasonality***

**The observed climate trends over the U.S. **
**can be mostly explained by changes in SST**

- 3-mon RunMean

- 3-mon RunMean

- Thin colored line:
- 14 indv members

## Chen et al. (2007a, b), J. Climate, Accepted

- Chen *et al*. (2007a, b), *J. Climate, Accepted*

**Leading SST EOFs: Global Warming (GW) and Pacific Decadal Variability (PDV)**
**Hadley SST; 1901-2000**

- 32%

- 12%

## Input for a set of idealized AGCM experiments

**Global Warming (GW)**

**Decadal Variability (DV)**

**Total**

**Residual**

**Input for a set of idealized AGCM experiments**

**Linear trend of SST: Total=GW+DV+Residual**
**Hadley SST; 1950-2000**

- EOF3+EOF4

## Idealized AGCM Experiments

| Experiments | SST |
| --- | --- |
| Control | SSTClim(monthly SST climatology over 1944-1976) |
| Total | SSTClim+SSTA_Total(linear change of SST over Jan1950-Dec2000) |
| Global Warming (GW) | SSTClim+SSTA_GW(linear change of SST associated with GW EOF) |
| Uniform Warming | SSTClim+0.32K |
| Decadal Variability (DV) | SSTClim+SSTA_DV(linear change of SST associated with DV EOF) |
| DV in Pacific | SSTClim+SSTA_DV_Pac(linear change of SST associated with DV in Pacific) |
| Residual | SSTClim+SSTA_Residual(SSTA_Total - SSTA_GW - SSTA_DV) |

**Idealized AGCM Experiments**

-  All runs are integrated for 100 years
-  Data averaged over the last 60 years taken as climatology
-  Climatological difference between control run and an anomaly run represents
-   effect of corresponding SST trend

**NASA NSIPP-1 AGCM; 3deg**

## Total

**Surface Air Temperature (T) Response in Idealized AGCM Experiments**

**Total**

**GW**

**DV**

**Residual**

**DJF**

**MAM**

**JJA**

**SON**

## Precip (P) Response in Idealized AGCM Experiments

**Precip (P) Response in Idealized AGCM Experiments**

**DJF**

**MAM**

**JJA**

**SON**

**Total**

**GW**

**DV**

**Residual**

## Seasonality (amplitude) in Idealized AGCM Experiments

**Seasonality (*****amplitude*****) in Idealized AGCM Experiments**

**GW: **
** ****lead to general warming**
** ****spatial pattern unimportant**
**DV **
** ****dominant for all seasons**
** ****mainly from Pacific**
**Residual**
** ****important in fall**
** ****mainly from NH tro Atlantic (not shown)**

- Total

- AMIP

## Seasonality (spatial pattern) in Idealized AGCM Experiments

- Spatial Pattern Correlation btw
- AGCM(Total_SSTA) and:
- AMIP_EnsMean
- AGCM(GW_SSTA)
- AGCM(0.32K_SSTA)
- AGCM(DV_SSTA)
- AGCM(DV_SSTA_Pacific)
- AGCM(Residual_SSTA)

**Seasonality (*****spatial pattern*****) in Idealized AGCM Experiments**

## Conclusions

- The observed climate trends over the U.S. during 1950-2000 exhibit distinct seasonality and regionality. In particular, there are notable cooling and wetting trends in late summer and fall.
- The observed climate trends can be mostly explained by changes in SST.
- Among the leading SST patterns:
- Global Warming (GW):
- does not contribute; mainly leads to a general warming trend
- spatial pattern unimportant
- Pacific Decadal Variability (PDV):
- plays a prominent role throughout all seasons
- Residual:
- mainly contribute in late summer and fall; contribution in fall comparable to that of PDV