Every month, I update the global temperature trend using satellite data reported by University of Alabama in Huntsville climatologists John Christy and Roy Spencer. The two have been reporting an overall upward trend in global average temperature of +0.140 degrees Celsius per decade since 1979. They have spent three years making various adjustments to the satellite data. A a consequence, they have now have lowered the upward trend in global average temperature to +0.114 degrees per decade. From the abstract:
Version 6 of the UAH MSU/AMSU global satellite temperature dataset is by far the most extensive revision of the procedures and computer code we have ever produced in over 25 years of global temperature monitoring. The two most significant changes from an end-user perspective are (1) a decrease in the global-average lower tropospheric (LT) temperature trend from +0.140 C/decade to +0.114 C/decade (Dec. '78 through Mar. '15); and (2) the geographic distribution of the LT trends, including higher spatial resolution.
Over at his blog, Roy Spencer further explains the results:
The gridpoint trend map above shows how the land areas, in general, have warmed faster than the ocean areas. We obtain land and ocean trends of +0.19 and +0.08 C/decade, respectively. These are weaker than thermometer-based warming trends, e.g. +0.26 for land (from CRUTem4, 1979-2014) and +0.12 C/decade for ocean (from HadSST3, 1979-2014).
Notice the trends decreased the most over the Northern Hemisphere extratropics, especially the Arctic, while tropical warming trends increased somewhat, especially over land. Near-zero trends exist in the region around Antarctica.
The new article concludes:
This should be considered a "beta" release of Version 6.0, and we await users' comments to see whether there are any obvious remaining problems in the dataset. In any event, we are confident that the new Version 6.0 dataset as it currently stands is more accurate anduseful than the Version 5.6 dataset.
The new LT trend of +0.114 C/decade (1979-2014) is 0.026 C/decade lower than the previous trend of +0.140 C/decade, but about 0.010 C/decade of that difference is due to lesser sensitivity of the new LT weighting function to direct surface emission by the land surface, which surface thermometer data suggests is warming more rapidly than the deep troposphere. The remaining 0.016 C/decade difference between the old and new LT product trends is mostly due to the new diurnal drift adjustment procedure and is well within our previously stated range of uncertainty for this product's trend calculation (+/-0.040C/decade).
We have performed some calculations of the sensitivity of the final product to various assumptions in the processing, and find it to be fairly robust. Most importantly, through sensitivity experiments we find it is difficult to obtain a global LT trend substantially greater than +0.114C/decade without making assumptions that cannot be easily justified.
It would be very good news if the pace of global warming was at this lower rate. If the new UAH figures hold up to scrutiny, they would further call the accuracy of higher projections of future temperatures made by computer climate models into question.
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