University of Alabama climatologists have released the newest version of their satellite temperature datasets. Interestingly enough, the updated satellite data came with a surprise: it lowered the Earth’s warming trend.

Version 6 of the satellite data shows faster warming in the early part of the satellite record, which stretches from Dec. 1978 to March. 2015, but shows reduced, or even eliminated, warming in the latter part of the record, wrote climatologists Roy Spencer, John Christy and William Braswell. UAH Version 6 satellite data now shows a decreased warming trend of 0.114 degrees Celsius per decade, compared to Version 5.6’s 0.140 degree trend.

This includes a decrease in the warming trend for the U.S. since the late 1970s. Spencer, Christy and Brasell noted that the U.S. “trend decreased from +0.23 to +0.17 C/decade” and the “Arctic region changed from +0.43 to +0.23 C/decade.”

“Near-zero trends exist in the region around Antarctica,” according to the UAH scientists.

“Note that in the early part of the record, Version 6 has somewhat faster warming than in Version 5.6, but then the latter part of the record has reduced (or even eliminated) warming, producing results closer to the behavior of the [Remote Sensing Systems] satellite dataset,” the scientists wrote.

“This is partly due to our new diurnal drift adjustment, especially for the NOAA-15 satellite,” the scientists added. “Even though our approach to that adjustment (described later) is empirical, it is interesting to see that it gives similar results to the RSS approach, which is based upon climate model calculations of the diurnal cycle in temperature.

Version 6 also shows that land areas have warmed faster than ocean areas. Land areas have warmed at a rate of 0.19 degrees Celsius per decade while ocean areas have only warmed at 0.08 degrees per decade — both of these, however, are below warming trends shown by surface thermometer data.

The updated UAH satellite temperature data comes as scientists are looking into allegations of data tampering by government climate agencies, like NASA and NOAA. Scientists skeptical of man-made global warming argue that data adjustments made by climate agencies may not be scientifically justified.

“Many people have found the extent of adjustments to the data surprising,” Terence Kealey, former vice-chancellor of the University of Buckingham, said in a statement released by The Global Warming Policy Foundation.

Skeptics argue that NOAA, for example, makes adjustments that artificially cool past temperature data while warming more recent records. This creates a significantly bigger warming trend than is borne out in the raw temperature data, argue skeptics.

“While we believe that the 20th century warming is real, we are concerned by claims that the actual trend is different from – or less certain than – has been suggested,” said Kealey, who has been appointed chairman of the foundation’s investigative task force. “We hope to perform a valuable public service by getting everything out into the open.”

NOAA justifies these adjustments by saying they are necessary to correct for “biases” in the raw data. Corrections made by NOAA help make the data more accurate, they argue. NOAA’s temperature readings are based on surface thermometers from weather stations, buoys and such.

Spencer himself has questioned climate data adjustments made by NOAA, but acknowledges adjustments to raw data (whether from weather stations or satellites) are necessary for accuracy. That is, if the problem can be proven to exist.

“Being the co-developer of a climate dataset (UAH satellite temperatures) I understand the need to make adjustments for known errors in the data … when you can quantitatively demonstrate an error exists,” Spencer wrote in March.

“But a variety of errors in data measurement and collection would typically have both positive and negative signs,” Spencer and his colleagues wrote. “In contrast, the thermometer data apparently need to be adjusted in such a way that almost always leads to greater and greater warming trends.”

Satellite data also needs adjustments, hence the recent update. For example, satellites need to be recalibrated, their orbits change, and they experience channel failures. This also means software and methodology updates as well.

“After 25 years of producing the UAH datasets, the reasons for reprocessing are many,” the scientists wrote. “That is no longer possible, and an explicit correction for diurnal drift is now necessary. The correction for diurnal drift is difficult to do well, and we have been committed to it being empirically–based, partly to provide an alternative to the RSS satellite dataset which uses a climate model for the diurnal drift adjustment.”

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