Past, Present, and Future Climate Change: Can Palaeoecology Help Manage a Warming World? - Biodiversity Conservation and Environmental Change - page 92

emissions are taken into consideration (Figure 5.4). We also know that the next glacial
period will not begin for at least another 30,000 years (Jansen et al. 2007)—so we cannot
rely on orbital factors to counteract the effects of anthropogenic greenhouse gas emissions.
Insights from past interglacial periods can help predict ecological responses to warming
and might also help in planning sustainable agriculture and settlement patterns. A study
from the Altiplano ('High Plain') of Peru and Bolivia provides an excellent example of this.
Lake Titicaca is the world's highest great lake, lying at an altitude of 3,810 m, and covering an
area of 58,000 km 2 . The presence of the lake adds moisture to the surrounding atmosphere,
buffers extremes of temperature, and warms the local environment today by 4-5 °C (Binford
et al. 1997). These effects on local climate created the favourable conditions that allowed agri-
culture to emerge in the region about 3,500 years ago, when conditions became wet enough
to support crop cultivation. The Altiplano remains one of the highest agricultural regions in
the world, providing livelihoods for over 2 million people and supplying quinoa, potato,
dairy, and meat, and supporting camelid systems such as alpaca and llama. Despite the rela-
tively moist conditions sustained by Lake Titicaca (Bush et al 2010), cultivation of crops is
limited by the short rainy season, the high level of evapotranspiration, and the low water
holding capacity of the soils (García et al. 2007). Hence, future changes in temperature and
aridity are of critical importance for the productivity and food security of the region.
Past interglacials provide an intriguing insight into two alternative scenarios that may
emerge in a warming climate. Bush et al. (2010) studied vegetation change over the past
370,000 years in the area surrounding Lake Titicaca. An upslope migration of plant and ani-
mal communities would be predicted in a warming climate, but the palaeo-record showed
that this was not the case in all of the interglacial periods. In two of the interglacials, Marine
Isotope Stages (MIS) 9 (starting 337,000 years ago) and 5e (about 123,000 years ago), a tipping
point was reached when, instead of migrating upslope, vegetation completely reorganized to
an arid adapted community (Figure 5.5). Bush et al. propose that falling lake levels reduced
the buffering effect on temperature, and caused regional cooling and aridification, associated
with a turnover in the plant community when a tipping point in aridity and temperature was
reached. Thus, the warming climate had two alternative outcomes—the aridification and
cooling effect of falling lake levels countering global trends of increasing temperature.
The study shows how important regional and local processes are in mediating the effects
of global climate change, and suggests that such a tipping point may well occur again. If
temperatures warm by 1-2 °C (Bush et al. 2010), cool and arid conditions may prevail, with
serious implications for the future of agriculture on the Altiplano, which is extremely sensi-
tive to climatic conditions. The agricultural potential of the Altiplano is already marginal,
with crop production only possible for 4-5 months per year and limited by rainfall season
and the onset of frosts (García et al. 2007, Gilles et al. 2013). The forecast 2 °C warming is
therefore likely to stress the system further, as occurred in the MWP, when a prolonged
warm, dry period contributed to the collapse of the Tiwanaku civilization of the Altiplano.
During this time, water levels of Lake Titicaca fell by 12-17 m, agricultural production plum-
meted and raised fields that had sustained the society for over 1,000 years were abandoned
(Binford et al. 1997).