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UN ECA - CILSS – ACMAD - IRI
Conference on Reduction of vulnerability of West Africa to climate change
Ouagadougou, January 24-27 2007
A climate scientist's perspective on recent environmental trends
in the Sahel: a model for future change?
Alessandra Giannini
IRI for Climate and Society (IRI)
The Earth Institute at Columbia University
Outline – past, present and future of climate in the Sahel
1. oceanic forcing dominant in late 20th century droughts
- what role for land-atmosphere interaction?
2. late 20th century response to anthropogenic forcings
- roles of GreenHouse Gases and (sulfate) aerosols
3. why the uncertainty in projections of future change?
- mechanisms of monsoon change under climate change
r = 0.60
A. Giannini, R. Saravanan and P. Chang, 2003. Science, 302, 1027-1030
Also see e.g. Bader and Latif, 2003 (GRL); Lu and Delworth, 2005 (GRL);Tippett, 2006 (GRL)
land-atmosphere interaction: is it a positive feedback?
(soil moisture, vegetation, dust..., evaporation, cloud cover...)
late 20th century surface temperature changes
regression of NASA/NSIPP1 Sahel PC and sfc temp
Giannini et al. 2003, 2005
NASA/GISS analysis of surface temp – linear trend 1950-2000
Hansen et al. 1999 (J. Geophys. Res.)
IPCC 4AR: end 20th century – PreIndustrial sfc temp difference
Biasutti and Giannini 2006 (GRL)
IPCC 4AR simulations – late 20th century climate change
19 Coupled GCMs
XX-PI Changes
Biasutti and Giannini, GRL 2006
20th century
Biasutti and Giannini, 2006 (GRL)
Sahel climate change
21st century
19 Coupled GCM (IPCC 4AR):
recent and future temperature
changes
A1B
(end 21st)
- end 20th
end 20th
- PreInd
CONCLUSIONS (climate science)
●
African climate variability and change are inextricably tied
to variations and trends in the global climate system:
-->> recent trends in the global oceans and in continental precipitation can
in part be ascribed to anthropogenic forcings
-->> drought in the Sahel was forced by a warming of the oceans, in no
negligible part due to GHG and aerosol forcing
“Farmers freed of blame for Sahel drought” in http://www.scidev.net/
CONCLUSIONS (climate science informing policy)
●
Climate change is already here the recent climate shift in the Sahel is a prime example of
potential changes to come, as the global climate system
responds to anthropogenic forcings
-->> regional institutions/CILSS have an opportunity to take advantage of the
lessons learned from managing the climate shift of the last ~30 years
-->> harmonization of desertification and climate change issues is overdue!
CONCLUSIONS (climate science informing practice - climate risk management)
collaborate on climate science
● improve (two-way) communication
●
-->> between climate scientists and policymakers
-->> between climate scientists and stakeholders in sectors vulnerable to climate
http://iridl.ldeo.columbia.edu/index.html
http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php
West Africa:
0-20N, 20W-20E
Eastern eq Africa:
10S-10N, 20-50E
Southern Africa:
25-10S, 20-40E
West Africa:
0-20N, 20W-20E
Eastern eq Africa:
10S-10N, 20-50E
Southern Africa:
25-10S, 20-40E
Courtesy of Todd Mitchell, UW/JISAO
Giannini et al., 2005 (Clim. Dyn.)
The relative roles of Atlantic, Indian and Pacific SSTs
Lu and Delworth, 2005 (Geophys. Res. Lett.)
GFDL CM2.0
Held et al., PNAS 2005
GMAO(NSIPP1)
NCAR CAM3
surface
air temperature
(minus global mean)
precipitation
Haarsma et al., GRL 2005
2050-2080 minus 1950-1980