Earth's Temperature History: How Well Is It Known?
Volume 8, Number 25: 22 June 2005
The primary empirical evidence (as opposed to the theoretical predictions derived from climate models) for believing that "business as usual," with respect to anthropogenic CO2 emissions, will produce unprecedented global warming and lead to a host of catastrophic consequences (which are typically claimed to be more serious than nuclear warfare and global terrorism) is the temperature history of the planet over the past millennium, which is typically depicted by climate alarmists as slowly declining for approximately nine hundred years and then rising dramatically to unprecedented levels over the course of the 20th century. We have long criticized this representation of the planet's climatic history for ignoring the non-CO2-induced millennial-scale oscillation of climate that produced the Medieval Warm Period of a thousand years ago, the subsequent Little Ice Age and, last of all, the Modern Warm Period (which climate alarmists largely attribute to anthropogenic CO2 emissions). A new paper by Esper et al. (2005) now adds another dimension to this important subject.
The team of two Swiss and two British scientists began by selecting four representations of earth's surface air temperature history over the past thousand years (Jones et al., 1998; Mann et al., 1999; Briffa, 2000; Esper et al., 2002) for inclusion in an analysis designed to reveal the significance of problems associated with some of those histories that rarely make their way into public discussions, noting that "these records were developed using tree ring data alone or using multi-proxy data, and are reported to represent different regions (e.g. Northern Hemisphere (NH) extra-tropics, or full NH)," thereby highlighting two of several factors (different types of data, different areas of applicability) that lead to different results. Other sources of divergent results that Esper et al. (2005) investigated were methodological differences, including "using scaling or regression, the calibration time period, and smoothing data before calibration." They also point out that different histories sometimes represent different seasons of the year, that they either include or exclude sea surface temperatures, that the available data are "more uncertain back in time," and that the average temperature as one travels back in time "becomes biased towards Europe, North America, and areas in Asia."
Volume 8, Number 25: 22 June 2005
https://www.co2science.org/articles/V8/N25/EDIT.php
