Abstract
From 1950 to 1987 a strong relationship existed between the El Nino-Southern Oscillation (ENSO) and HadCRUT4 global average temperature anomaly, interrupted occasionally by volcanic erup-tions. After 1987 the relationship diverged, with temperature anomaly increasing more than ex-pected, but was re-established after 1997 at an offset of ~0.48°C higher. The period of increased warming from 1987 to 1997 loosely coincided with the divergence of the global average tempera-ture anomalies over land, which are derived from observation station recordings, and the global average anomalies in sea surface temperatures. Land-based temperatures averaged 0.04°C below sea temperatures for the period 1950 to 1987 but after 1997 averaged 0.41°C above sea tempera-tures. The increase in the global average temperature anomaly and the divergence of land and sea surface temperatures also coincided with two significant changes in global average cloud cover. Total cloud cover decreased during the period from 1987 to 1997 and, for most of the remainder of the period from 1984 to 2009, decreases in low-level cloud were accompanied by increases in middle and upper level cloud. These changes can be found in both global average cloud cover and in each of the six 30°C-latitude bands. The impact of these changes in cloud cover can account for the variations in HadCRUT4 global average temperature anomalies and the divergence between land and sea temperatures.
Highlights
The latest report by the Intergovernmental Panel on Climate Change (IPCC, 2013, [1]) reports that some climate models overestimate the climate system’s response to increasing greenhouse gases since 1998, in other wordsHow to cite this paper: McLean, J. (2014) Late Twentieth-Century Warming and Variations in Cloud Cover
This paper will attempt to address the wider issue of variation in cloud cover at all levels and in total, and whether this relates to variations in the HadCRUT4 global average temperature anomaly
The Troup SOI data is preferred to the 3-month average of sea surface temperatures in the “Nino 3.4” region because prior to 1957 data coverage of this region rarely exceeded 50% and was less than 75% for many years after, the shortfall being mainly in the western half of this region, which might have been the only portion impacted by mild El Nino-Southern Oscillation (ENSO) events
Summary
The latest report by the Intergovernmental Panel on Climate Change (IPCC, 2013, [1]) reports that some climate models overestimate the climate system’s response to increasing greenhouse gases since 1998, in other words. Relevant papers include Goode and Pallé [5], who briefly discussed variations in cloud cover as part of larger paper focusing largely on variations in solar radiation. Kauppinen et al [7] discussed the impact of both humidity and cloud cover on the global mean surface temperature. Eastman and Warren discuss long-term trends in cloud over sea [8] and land [9] The former focuses on marine stratus and stratocumulus cloud cover when discussing variations in sea surface temperature and the later mentions temperature only very briefly. This paper will attempt to address the wider issue of variation in cloud cover at all levels and in total, and whether this relates to variations in the HadCRUT4 global average temperature anomaly. Volcanic eruptions and the El Nino-Southern Oscillation (ENSO) are recognised influences on temperature so those influences will be identified and removed before the relationship between the residual temperature and variations cloud cover is considered
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