UN ECA - CILSS – ACMAD - IRIConference on Reduction of vulnerability of West Africa to climate change

Ouagadougou, January 24-27 2007

A climate scientist's perspective on recent environmental trendsin the Sahel: a model for future change?

Alessandra GianniniIRI 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, 1027-1030Also 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...)

NASA/GISS analysis of surface temp – linear trend 1950-2000Hansen et al. 1999 (J. Geophys. Res.)

regression of NASA/NSIPP1 Sahel PC and sfc tempGiannini et al. 2003, 2005

IPCC 4AR: end 20th century – PreIndustrial sfc temp differenceBiasutti and Giannini 2006 (GRL)

late 20th century surface temperature changes

19 Coupled GCMs XX-PI Changes

Biasutti and Giannini, GRL 2006

IPCC 4AR simulations – late 20th century climate change

Biasutti and Giannini, 2006 (GRL)

Sahel climate change20th century 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.htmlhttp://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.)

Lu and Delworth, 2005 (Geophys. Res. Lett.)

The relative roles of Atlantic, Indian and Pacific SSTs

Held et al., PNAS 2005

GFDL CM2.0 GMAO(NSIPP1) NCAR CAM3

surface air temperature

(minus global mean)

precipitation

Haarsma et al., GRL 2005 2050-2080 minus 1950-1980