What Waitomo speleothems tell us about environmental change
University of Auckland
Email: p.williams@auckland.ac.nz
Abstract
The most important information that speleothems can reveal is about climate. These days we hear a lot about climate change and what’s likely to happen in the near future, but most evidence is derived from the Northern Hemisphere and we’re not sure if predictions really apply downunder. So we need to determine if known NH climate events (like the Medieval Warm Period and Little Ice Age) are found in the SH. If this can be confirmed then it increases the likelihood that climate predictions will apply to both hemisphere – even if there are leads or lags in events. To reach unambiguous conclusions about this we need well dated high resolution data from the SH that can be compared to data of similar quality from the NH. The best interval to examine is the last 2000 years, because that’s when the NH has its most accurate historical data and it’s also the period of most relevance to our near future. This contribution will therefore focus on evidence from a 29.4 mm long section of a small stalagmite from Waitomo that grew from 59 BC to 2005 AD. It shows that temperature changes at Waitomo have been generally asynchronous with respect to the NH, except in the 20th Century when warming occurred in both hemispheres. Recent ‘global warming’ started in Waitomo about 1913 (25 years later than in the NH), but both the amount and rate of warming through last century was not unusual in the context of the last 2 millennia. It was about as warm and sometimes warmer around 1840, 1380 and 750 AD. The general conclusion is that on a centennial scale the SH and NH are generally out of phase, except in the 20th Century when global warming affected us both. although starting slightly later and being less severe (so far?) in NZ.