Impact of global warming on the interannual and interdecadal climate modes in a coupled GCM

Abstract

In this study, we investigated the impact of global warming on the variabilities of large-scale interannual and interdecadal climate modes and teleconnection patterns with two long-term integrations of the coupled general circulation model of ECHAM4/OPYC3 at the Max-Planck-Institute for Meteorology, Hamburg. One is the control (CTRL) run with ®xed present-day concentrations of greenhouse gases. The other experiment is a simulation of transient greenhouse warming, named GHG run. In the GHG run the averaged geopotential height at 500 hPa is increased signi®cantly, and a negative phase of the Paci®c/North American (PNA) teleconnection-like distribution pattern is intensi®ed. The standard deviation over the tropics (high latitudes) is enhanced (reduced) on the interdecadal time scales and reduced (enhanced) on the interannual time scales in the GHG run. Except for an interdecadal mode related to the Southern Oscillation (SO) in the GHG run, the spatial variation patterns are similar for dierent (interannual + interdecadal, interannual, and interdecadal) time scales in the GHG and CTRL runs. Spatial distributions of the teleconnection patterns on the interannual and interdecadal time scales in the GHG run are also similar to those in the CTRL run. But some teleconnection patterns show linear trends and changes of variances and frequencies in the GHG run. Apart from the positive linear trend of the SO, the interdecadal modulation to the El NinÄ o/SO cycle is enhanced during the GHG 2040 $ 2099. This is the result of an enhancement of the Walker circulation during that period. La NinÄ a events intensify and El NinÄ o events relatively weaken during the GHG 2070 $ 2090. It is interesting to note that with increasing greenhouse gas concentrations the relation between the SO and the PNA pattern is reversed signi®cantly from a negative to a positive correlation on the interdecadal time scales and weakened on the interannual time scales. This suggests that the increase of the greenhouse gas concentrations will trigger the nonstationary correlation between the SO and the PNA pattern both on the interdecadal and interannual time scales.

The intensification and shift of the annual North Atlantic Oscillation in a global warming scenario simulation

“…However, observational studies have shown that the winter NAO can be characterized as having a weakly red spectrum with some long-range dependence (Stephenson et al, 2000;Stephenson and Pavan, 2003). Figures 3 and 4 also show no significant differences of NAO behavior between the first and second halves of the model integration, which is consistent with previous results (Ulbrich and Christoph, 1999;Hu et al, 2001). Disagreement between Figs.…”

“…Ulbrich and Christoph (1999) found that the disagreement between the NAO index change and the storm track intensification results from the northeastward shift of the northern center of action of the NAO. By examining the same scenario run, Hu et al (2001) also found that there is no significant change of the NAO index. Zorita and González-Rouco (2000) demonstrated the disagreement of the simulated long-term trends of the AO intensity between the HadCM2 and ECHAM4/OPYC CGCMs, although the simulated winter temperature increases averaged over the NH in the two models are very similar.…”

“…Ulbrich and Christoph (1999) found that the shift of the northern active center of the NAO and the intensification of storm track activity over Europe resulted from the increase of greenhouse gas concentrations. Hu et al (2001) examined the impact of the global warming on the trend, the standard deviation, and climate modes of geopotential height at 500 hPa in winter. Christoph et al (2000) analyzed the control run and indicated that the model produces a realistic spatial pattern and temporal evolution of the NAO.…”

“…Further analysis will help us to understand the NAO change in the global warming scenario. Using the same scenario simulation of the ECHAM4/OPYC3 CGCM used by Ulbrich and Christoph (1999), Zorita and González-Rouco (2000), and Hu et al, (2001), we further examine the impact of increasing greenhouse gas concentrations on the temporal and spatial change of the NAO, including the possible changes of the NAO intensity and frequency, and the location shift of the two centers of action of the NAO. In Section 2, the model, data, and methods are briefly described.…”

Projections of future climate change

“…Attempts to address this question using climate models have again shown conflicting results, varying from slight decreases or little change in amplitude (Tett 1995;Knutson et al, 1997;Noda et al, 1999b;Collins, 2000b;Washington et al, 2001;Figure 9.26b) to a small increase in amplitude (Timmermann et al, 1999;Collins, 2000a; Figure 9.26a), which has been attributed to an increase in the intensity of the thermocline in the tropical Pacific. Knutson et al (1997) and Hu et al (2001) find that the largest changes in the amplitude of ENSO occur on decadal time-scales with increased multi-decadal modulation of the ENSO amplitude. Several authors have also found changes in other statistics of variability related to ENSO.…”