Volume 16, Number 8: 20 February 2013
Climate alarmists are striving mightily to convince the nations of the world that mean global sea level has recently begun to rise at a faster-than-usual "unnatural" rate, as a result of an increased melting of glaciers and ice sheets due to global warming that they claim has been driven by ever-increasing anthropogenic-induced emissions of greenhouse gases, the most prominent of which is carbon dioxide or CO2. But is this really the case?
In a study of inter-annual and decadal variability in Pacific Ocean sea level trends, Zhang and Church (2012) drive another nail into the coffin of the climate alarmists' untenable contention. They begin by noting that "many sea level studies have an underlying purpose [italics added] of detecting and quantifying sea level change due to anthropogenic climate change [italics added]," but they note that "on a regional scale, such a signal is mixed with that due to natural climate variability," and "as a result, it is extremely difficult to separate the natural and anthropogenic signals, especially when they have comparable amplitudes and the available time series is short relative to the period of the natural variability."
This latter problem has become especially serious since the launch of the Topex/Poseidon altimeter, with many researchers detecting regional linear trends in sea level rise from altimeter data over time spans ranging from a mere 3 to 18 years, and where Zhang and Church report that in some locations "the linear trend over 1993-2009 based on altimeter measurement can be five times the global average [italics added]," citing Church et al. (2010).
To better elucidate the seriousness of this problem, Zhang and Church used continuous near-global altimeter measurements since 1993 to attempt to separate inter-annual and decadal sea level variability in the Pacific from the long-term background sea level trend; and in doing so, they were able to show that "the decreasing regional sea level in the eastern equatorial Pacific is mainly associated with the Pacific Decadal Oscillation," while "in contrast, for those island countries in the western tropical Pacific and especially low-lying atolls, the high rate of sea level rise over the altimeter era has a significant component associated with natural variability."
In light of their illuminating findings, the two Australian researchers thus conclude that "it is tempting to use current-day altimeter-based regional sea level linear trends as a reference for future climate change projections." However, they say that "such practice needs to be treated with caution as regional sea level linear trends derived over the short altimeter era can be greatly affected by low-frequency climate variability."
Sherwood, Keith and Craig Idso
Church, J.A., Aarup T., Woodworth, P.L., Wilson, W.S., Nicholls, R.J., Rayner, R., Lambeck, K., Mitchum, G.T., Steffen, K., Cazenave, A., Blewitt, G., Microvica, J.X. and Lowe, J.A. 2010. Sea-level rise and variability: Synthesis and outlook for the future. In: Church, J.A., Woodworth, P.L, Aarup, T. and Wilson, W.S. ( Eds.) Understanding Sea-Level Rise and Variability, Wiley-Blackwell, Chichester, United Kingdom, pp. 402-419.
Zhang, X. and Church, J.A. 2012. Sea level trends, interannual and decadal variability in the Pacific Ocean. Geophysical Research Letters 39: 10.1029/2012GL053240.