Geoscience Reference
In-Depth Information
freshwater cycle via a freshwater flux field (invariant in time) that is applied to the ocean
(e.g., HadGEM2 Development Team
2011
). This is necessary because there is no explicit
representation in the model of the flow of ice from accumulation regions to iceberg calving
at the coast.
The challenge for inclusion of ice sheets in GCMs is to develop the physical processes of
interaction between ice sheets and oceans. It is this interaction that has caused the thinning of
ice shelves and the speed-up of peripheral glaciers in both Greenland and Antarctica. The
West Antarctic ice sheet is grounded below sea level and 3 m of sea level rise could result with
glacial calving exceeding the supply of ice from the interior, as the coastline retreats pole-
ward. Ice sheet models (e.g., Rutt et al.
2009
) are being used to investigate the contribution of
glacier speed-up and increased ice discharge as icebergs to sea level rise.
Mountain glaciers and ice caps include only a minor fraction of all water on Earth
bound in glacier ice (\1 %) compared with the Antarctic and Greenland ice sheets
([99 %), but their retreat has dominated the eustatic sea level contribution in the past
century (Meier et al.
2007
). Mountain glacier schemes are being developed and used
alongside climate change models to make projections of future changes in sea level due to
volume changes in mountain glaciers and ice caps (e.g., Radi
ยด
and Hock
2011
).
Sea ice plays an important role in the climate system through high surface albedo,
insulating the ocean, and influencing the ocean salinity through brine rejection when ice
forms and surface freshening when ice melts. Changes in sea ice under a warming scenario
significantly influence the local water cycle. The Los Alamos sea ice model, CICE, has
been introduced into a number of climate models (e.g., Hewitt et al.
2011
; Holland et al.
2012
). The use of this community model means that implementations of new physics can
be shared but still allows different modelling centres to use different dynamics and
parametrisations, maintaining model diversity.
2.3.5 Global Monsoons
The monsoons in India, Africa, East Asia represent the largest seasonal redistribution of
water within the hydrological cycle. They are also crucial to the economies of those
countries and the livelihoods of the local population. Accurate predictions of monsoon
onset, variations within the season and the overall seasonal rainfall amount and its regional
distribution, and how these may change in the future, are required for effective agricultural
and water resource management. We therefore focus this sub-section on the wide-ranging
studies of monsoon processes that are underway around the world.
The monsoons are complex large-scale climate phenomena whose simulation has
proved a challenge for modellers for several decades. Many studies have shown sensitivity
to convection and boundary layer parametrisation (e.g., Mukhopadhyay et al.
2010
and
references therein; Hong
2010
and references therein), cloud microphysics and land sur-
face properties (e.g., Douville et al.
2001
; Yasunari et al.
2006
), as well as model resolution
(e.g., Kim et al.
2008
). Idealised sensitivity experiments have shed light on the major
forcing regions, such as orographic forcing from the Himalayas and the Tibetan plateau
(e.g., Boos and Kuang
2010
) and the western Ghats (e.g., Wang and Chang
2012
), land-sea
contrasts between the Indian peninsula and the surrounding ocean, and sea surface tem-
perature forcing from the Arabian Sea, Bay of Bengal and the equatorial Indian Ocean
(Levine and Turner
2011
).
Analysis of the impact of changes to convection parametrisation has provided insight
into how problems with the distribution of precipitation intensity affect mean monsoon
rainfall biases. For example, Mukhopadhyay et al. (
2010
) showed that different seasonal
