Thanks to Jos de Laat of KNMI for alerting us to the paper
Paeth, H., K. Born, R. Girmes, R. Podzun, and D. Jacob, 2009: Regional Climate Change in Tropical and Northern Africa due to Greenhouse Forcing and Land Use Changes. J. Climate, 22, 114–132.
The abstract reads
“Human activity is supposed to affect the earth’s climate mainly via two processes: the emission of greenhouse gases and aerosols and the alteration of land cover. While the former process is well established in state-of-the-art climate model simulations, less attention has been paid to the latter. However, the low latitudes appear to be particularly sensitive to land use changes, especially in tropical Africa where frequent drought episodes were observed during recent decades. Here several ensembles of long-term transient climate change experiments are presented with a regional climate model to estimate the future pathway of African climate under fairly realistic forcing conditions. Therefore, the simulations are forced with increasing greenhouse gas concentrations as well as land use changes until 2050. Three different scenarios are prescribed in order to assess the range of options inferred from global political, social, and economical development. The authors find a prominent surface heating and a weakening of the hydrological cycle over most of tropical Africa, resulting in enhanced heat stress and extended dry spells. In contrast, the large-scale atmospheric circulation in upper levels is less affected, pointing to a primarily local effect of land degradation on near-surface climate. In the model study, it turns out that land use changes are primarily responsible for the simulated climate response. In general, simulated climate changes are not concealed by internal variability. Thus, the effect of land use changes has to be accounted for when developing more realistic scenarios for future African climate.”
Important findings from this paper include the text
“….most investigations of future African climate change have been focused on the impact of increasing greenhouse gas (GHG) concentrations, which usually satisfy the effect of warmer tropical oceans but neglect the role of land cover changes (Pielke et al. 2002). Several of the GHG induced experiments from global climate models predict a northward extension of moisture advection into the Sahel zone and more humid conditions (Kamga et al. 2005; Hoerling et al. 2006), but still with little agreement between different climate models (Hulme et al. 2001; Maynard and Royer 2004; Coppola and Giorgi 2005; Cook and Vizy 2006; Paeth et al. 2008)…..”
“….Hence, the question arises whether the classical procedure of the IPCC, namely, the assessment of anthropogenic climate change by prescribing rising GHG and aerosol concentrations, is sufficient for the prediction of future African climate (Pielke et al. 2002). Another important factor for climate change, particularly in the low latitudes, may be the changing land cover in the form of land use changes owing to human activity like agriculture, shifting cultivation, pasture, urbanization, and transport infrastructure (Feddema et al. 2005). On the other hand, land cover changes as a natural response to climate change, like, for example, albedo changes in high latitudes, may be crucial in the extratropical regions. Regional studies for the United States, China, and Europe have shown that urbanization, land use changes, and vegetation loss may enhance the amplitude of near-surface warming considerably by up to a factor of 2 (Zhao and Pitman 2002). In tropical Africa, however, the effect on the hydrological cycle would be more relevant.”
“Several authors have suggested that the prevailing droughts during the second half of the twentieth century
were at least partly caused by land cover changes in tropical and subtropical Africa (Zeng and Neelin 2000; Pielke 2001; Semazzi and Song 2001; Zeng et al. 2002).”
This paper clearly documents a failure of the 2007 IPCC reports to include the assessment of the role of all first order climate forcings on the climate system.