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Seminar Notice
Effects of vegetation change on climate and runoff
under rising CO2
Richard Betts,
Hadley Centre for Climate Prediction and Research, Met Office, UK
Wed 5 March 2003
11.00 am - 12 noon
Conference Room, C.S. Christian Laboratory
CSIRO Land and Water
Black Mountain Laboratory Canberra (Clunies Ross Street, Canberra)
'Assumptions are those things you don't know you're making' -
Douglas Adams
The Intergovernmental Panel on Climate Change (IPCC) scenarios
assume that climate change will not affect the current 50% negative
feedback on CO2 rise. This assumption has been examined by including
the global carbon cycle in the Hadley Centre climate model. When
this is driven by the IS92a emissions (not concentrations) scenario,
increased draw-down of CO2 into vegetation and soils is countered
by a warming-induced increased release of carbon through soil respiration.
Reduced Amazonian forest cover, under decreased precipitation, also
releases carbon. The result is a much smaller negative feedback
on CO2 rise than previously assumed. Global warming is therefore
faster than previously simulated.
Furthermore, future projections of runoff in an increased-CO2
world typically assume that the main driver will be precipitation
and evaporation changes associated with radiatively-forced climate
warming. This is despite previous work (eg: Hatton et. al., 1992)
showing that direct plant physiological responses to increased CO2
can exert major impacts on the surface water budget. The coupled
climate-carbon cycle model has been used to examine the relative
effects of radiative and physiological forcing of the water cycle
by CO2. It is found that global runoff may be affected more by vegetation
responses than climate.
Can the carbon-storage effects of forests on climate
be offset by changes in the absorption of solar radiation?
Richard Betts,
Hadley Centre for Climate Prediction and Research, Met Office, UK
Wednesday 5 March 2003
CSIRO Forestry and Forest Products, Theatrette
Building 1, Banks St, Yarralumla
Changes in forest cover can influence climate through the carbon
cycle and also through their influence on the physical properties
of the landscape. In particular, the presence or absence of forests
affects the proportions of solar radiation absorbed or reflected
by the land (the surface albedo), and therefore affects the warming
of the surface by the sun. A forested landscape typically absorbs
more solar radiation than unforested land, particularly in snowy
conditions when forest-free areas are very bright and reflective.
The motivation for using forests as carbon sinks is to reduce
the rate of climate warming. However, if forests can exert a direct
warming influence by modifying surface albedo, could this be large
enough to offset the cooling afforded by carbon sequestration? The
analysis presented here suggests that in some regions, the answer
to this is "yes". Clearly this has significant implications
for the Kyoto Protocol.
About Richard
Richard Betts has worked on biosphere-atmosphere
modelling at the Hadley Centre for 10 years. He coupled the TRIFFID
vegetation model into the Hadley Centre GCM, and uses this to investigate
atmosphere-biosphere interactions. His research interests also include
non-greenhouse forcings of the climate system, such as physiological
responses to CO2 and the physical effects of land cover
change on climate.
The seminar is starting at 3.30 pm. Join us for coffee prior to
the seminar between 3.00 - 3.30
Please join us for informal discussion and enjoy some refreshment
and nibbles after the seminar
Yarralumla Rostrum Club
CFFP Seminar Series Co-ordinators
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