Tuesday, September 10, 2013

New paper finds chaotic response to natural climate drivers ENSO and solar activity

A paper under open review for Climate of the Past reconstructs climate and levels of 9 lakes in East Africa and finds the climate of East Africa is highly complex with each lake demonstrating vastly different behavior over the past 1,000 years, despite essentially the same forcings from ENSO and solar activity. The authors also show, contrary to claims of climate alarmists, that ENSO/El Nino activity at the end of the 20th century was near the lowest levels of the past 1,000 years, and solar activity at the end of the 20th century was at the highest levels of the past 1,000 years. The authors find drought was more common during both the Medieval Warming Period and the peak period of the Little Ice Age in comparison to the end of the record in the year 2000. The paper debunks simplistic or false claims of climate alarmists such as "wet gets wetter, dry gets drier" or that climate drivers behave in a linear or non-chaotic fashion over time and space, finding instead, "The data highlight the complexity of individual lake response to climate forcing, indicating shifting drivers through time."

Top graph shows ENSO/El Nino frequency is currently near the lowest levels of the past 900 years. Second graph shows solar activity at the end of the 20th century was at the highest levels of the past 900 years. Remaining 9 graphs show chaotic & individualized climate response of lake levels in 9 different lakes in East Africa.
Fig. 5. Comparison of climate drivers (a, b) and regional lake levels in East Africa (c–h) to reconstructed lake levels from (j) Kyasanduka and (k) Nyamogusingiri (see also Table S1 in the Supplement).

Clim. Past Discuss., 9, 5183-5226, 2013

K. Mills1,2, D. B. Ryves1, N. J. Anderson1, C. L. Bryant3, and J. J. Tyler4
1Department of Geography, Loughborough University, Loughborough, LE11 3TU, UK
2School of Science and Engineering, University of Ballarat, 3350 Ballarat, Australia
3NERC Radiocarbon Facility (Environment), Scottish Enterprise Technology Park, East Kilbride, G75 0QF, Scotland, UK
4School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5001, Australia

Abstract. Equatorial East Africa has a complex, regional patchwork of climate regimes, with multiple interacting drivers. Recent studies have focussed on large lakes and reveal signals that are smoothed in both space and time, and, whilst useful at a continental scale, are of less relevance when understanding short-term, abrupt or immediate impacts of climate and environmental changes. Smaller-scale studies have highlighted spatial complexity and regional heterogeneity of tropical palaeoenvironments in terms of responses to climatic forcing (e.g. the Little Ice Age [LIA]) and questions remain over the spatial extent and synchroneity of climatic changes seen in East African records.

Sediment cores from paired crater lakes in western Uganda were examined to assess ecosystem response to long-term climate and environmental change as well as testing responses to multiple drivers using redundancy analysis. These archives provide annual to sub-decadal records of environmental change. The records from the two lakes demonstrate an individualistic response to external (e.g. climatic) drivers, however, some of the broader patterns observed across East Africa suggest that the lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Climate Anomaly (MCA; 1000–1200 AD) and a relatively drier climate during the main phase of the LIA (1500–1800 AD); though lake levels in western Uganda do fluctuate. The relationship of Ugandan lakes to regional climate drivers breaks down c. 1800 AD, when major changes in the ecosystems appear to be a response to sediment and nutrient influxes as a result of increasing cultural impacts within the lake catchments.

The data highlight the complexity of individual lake response to climate forcing, indicating shifting drivers through time. This research also highlights the importance of using multi-lake studies [very few do] within a landscape to allow for rigorous testing of climate reconstructions, forcing and ecosystem response.

1 comment:

  1. Warmer is not always wetter