The Mediterranean Basin in a warmer and drier world: what can we learn from the past?

J. Guiot, CNRS, CEREGE, Aix-en-Provence, France

D. Kaniewski, University of Toulouse 3, Ecolab, Toulouse, France

Introduction

• History shows that access to water resources has always presented a challenge for societies around the Mediterranean throughout the Holocene (roughly the last 10,000 years).

• Repeatedly, adverse climate shifts seem to have interacted with social, economic and political variables, exacerbating vulnerabilities in drier regions.

• We present a reconstruction of the Holocene climate in the Mediterranean Basin using an innovative method based on pollen data and vegetation modeling.

• This model inversion is particularly suited to deal with increasing dissimilarities between past millennia and the last century, especially due to a direct effect of CO2 on vegetation.

The Sea Peoples at the end of the Bronze Age

289 sites

Mainly in North Med Basin

55 levels / site in average

Pollen series from the European Pollen Database (EPD) for the last 10 ka BP.

Climate grid (81 points)

Prior and posterior probability distribution: Bayesian approach

100 150 200 250 300 350 400

0.0

00

0.0

05

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0.0

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Prior Prob of Pann (modern, 1°W, 35°N)

Pann (mm)

De

nsity

Biome4 Pollen

data

Δ = 200 mm Δ = 30 mm

Model + data

Large uncertainties narrower uncertainties

-0.35 -0.30 -0.25 -0.20 -0.15 -0.10

02

46

810

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LH Distribution (modern, 1°W, 35°N)

N = 202 Bandwidth = 0.009857

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nsity

100 150 200 250 300 350 400

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.01

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.04

Posterior Prob of Pann (modern, 1°W, 35°N)

Pann (mm)

De

nsity

Validation on modern data

R2=0.76

R2=0.55

- Underestimation of temperature and overestimation of precipitation partly because gridded modern climate is given at lower elevation than pollen sites - Solution: calculate anomalies from reconstructed modern climate rather than observed climate

Evolution of drought index across Holocene

Spread of neolithic culture

collapse of the Late Uruk colony

Palestinian cities decline Akkadian collapse

Late Bronze Age collapse

Medieval period

Little Ice Age

Conclusion

• The comparison of far past and last century shows that the intensity of century-scale precipitation fall, amplified by higher temperatures and then evapotranspiration, is unmatched over the last 10,000 years.

• The recent climatic change is then unprecedented during the last 10,000 years in the Mediterranean Basin.

• We show also that adverse climate shifts are often correlated with the decline or collapse of Mediterranean civilizations, particularly in the eastern Basin.

• The main consequence is that, over the next few decades, Mediterranean societies are likely to be much more critically vulnerable to climate change, than at any dry period of the past.