Description of the Medieval Warm Period and Little Ice Age in IPCC reports

Description of the Medieval Warm Period and Little Ice Age in IPCC reports image

A selection of temperature reconstructions published between 1998 and 2005

The description of the Medieval Warm Period and Little Ice Age in IPCC reports has changed since the first report in 1990 as scientific understanding of the temperature record of the past 1000 years has improved. The Medieval Warm Period (MWP) and Little Ice Age (LIA) are the best-known temperature fluctuations in the last millennium.

Critics of the "hockey stick graph" of all subsequent reports have claimed that the record of the MWP and LIA were suppressed in the IPCC Third Assessment Report although every report discussed the phenomena.

Contents

1990 report (FAR)

See also: IPCC First Assessment Report IPCC FAR 1990 Figure 7.1: Schematic diagrams of global temperature variations since the Pleistocene on three time scales (a) the last million years (b) the last ten thousand years and (c) the last thousand years The dotted line nominally represents conditions near the beginning of the twentieth century

With the growth of interest in global warming in the 1980s came renewed interest in the past temperature record as well as the question of whether past times had been warmer or colder than "present". However, available records were then few. In Chapter 7 "Observed Climate Variations and Change", the Executive Summary on page 199 noted that palaeo-climatic evidence indicated surface temperature "fluctuations including the Holocene Optimum around 5,000-6,000 years ago, the shorter Medieval Warm Period around 1000 AD (which may not have been global) and the Little Ice Age which ended only in the middle to late nineteenth century. Details are often poorly known because palaeo-climatic data are frequently sparse."

Section "7.2.7 Climate Of The Past 5,000,000 Years" of the report included, on page 202, "Figure 7.1: Schematic diagrams of global temperature variations since the Pleistocene on three time scales". The third diagram, figure 7.1 (c), used a schematic (non-quantitative) curve to represent temperature variations over the last 1000 years. The vertical temperature scale was labelled as "Temperature change (°C)" but no numerical labels were given; it could be taken to imply that temperature variations of the MWP and LIA were each of the order of 0.5:°C from the temperature around 1900. Text on the same page specifically stated recent climate changes were in a range of probably less than 2:°C. It noted that the "late tenth to early thirteenth centuries (about AD 950-1250) appear to have been exceptionally warm in western Europe, Ice... ...read more

This article is copied from an article on Wikipedia® - the free encyclopedia created and edited by its online user community. This article is distributed under the terms of GNU Free Documentation License.