Geoscience Reference
In-Depth Information
in simulations using parametrised convection and simulations using explicitly resolved
convection.
Increasing greenhouse gas concentrations are expected to enhance the interannual
variability of summer climate in Europe and other mid-latitude regions, potentially causing
more frequent heatwaves (e.g., Sch¨r et al.
2004
; Clark et al.
2010
). Seneviratne et al.
(
2006
) showed that the increase in summer temperature variability predicted in central and
eastern Europe is mainly due to feedbacks between the land surface and the atmosphere.
Furthermore, they suggested that land-atmosphere interactions increase climate variability
in this region because climatic regimes in Europe shift northwards in response to
increasing greenhouse gas concentrations, creating a new transitional climate zone with
strong land-atmosphere coupling in central and eastern Europe. This highlights the crucial
role of land-atmosphere interactions in future climate change.
Several of the climate models participating in CMIP5 include dynamic vegetation
models (e.g., Collins et al.
2011
). Systematic biases in the distribution and variability of
vegetation types in such models may affect surface fluxes of heat and moisture, which
themselves may influence atmospheric temperature and humidity profiles, thereby affect-
ing cloud formation. Large-scale circulation may also be affected, which could have an
impact on non-local sources of precipitation. Martin and Levine (
2012
) showed how South
Asian summer monsoon rainfall is affected by the inclusion of a dynamic vegetation
scheme in a member of the HadGEM2 model family. They found that systematic increases
in the bare soil fraction in key dust-producing regions, arising due to systematic dry rainfall
biases particularly over India, affected the monsoon circulation through changes in the
radiative balance, while changes in the needleleaf tree fraction over northern Eurasia also
affected the monsoon through changes in winter snow cover. Other work is also ongoing to
understand how such changes in the representation of the land surface during current and
past climate conditions may affect the projected changes in temperature and precipitation
in future.
2.3.3 Ocean-Atmosphere Processes and Interactions
The importance of coupled ocean-atmosphere interactions in climate variability and
change has long been established. Of particular importance is the simulation of the El
Nino-Southern Oscillation (ENSO), a coupled phenomenon whereby warming/cooling in
the tropical Pacific Ocean that takes place at intervals of 2-7 years is associated with a
large-scale tropical east-west seesaw in southern Pacific sea level surface pressure.
Although ENSO originates in the tropical Pacific, it affects global climate and weather
events such as drought/flooding and tropical storms. Therefore, understanding and pre-
dicting ENSO are crucial to both the scientific community and the public. Simulating the
time-mean properties in the tropics has continually been a challenge for coupled GCMs.
Though most models can internally generate the fundamental mechanisms that drive El
Ni ˜o properties, most models simulate a mean zonal equatorial wind stress that is too
strong and that has an annual amplitude that is also too strong (Guilyardi et al.
2009
). This
has profound effects on ENSO behaviour in that it limits the regimes in which interannual
anomalies can develop.
Persistent systematic errors have been noted in several generations of global coupled
models (Randall et al.
2007
). These include a double intertropical convergence zone
(ITCZ) pattern with excessive precipitation off the equator but insufficient precipitation on
the equator, which is often associated with an excessive and overly narrow sea surface
temperature (SST) cold tongue that extends too far west into the western Pacific. SST
