Climate contrarians who oppose taking action to slow global warming have focused their arguments on the past 18 years, during which time the warming of surface temperatures temporarily slowed down (it's now speeding back up). The latest version of the NOAA method to adjust the temperatures made the slowdown a little smaller, and that didn't sit well with those contrarians.
Lamar Smith soon began making conspiratorial accusations and demanding NOAA scientists' emails. Last week, he convened a hearing in the House Science Committee and claimed, with no supporting evidence or basis in reality,
An example of how this administration promotes its suspect climate agenda can be seen at the National Oceanographic [sic] and Atmospheric Administration. Its employees altered historical climate data to get politically correct results in an attempt to disprove the eighteen year lack of global temperature increases.
NOAA conveniently issued its news release that promotes this report just as the administration announced its extensive climate change regulations.
Study shows the adjustments work well
The new study published in Geophysical Research Letters by Zeke Hausfather of Berkeley Earth, Kevin Cowtan at the University of York, and Matthew Menne and Claude Williams Jr. at NOAA, set out to test how well the adjustments are working. Contrarians' biggest complaints focus on urban heat sources near land temperature stations, and scientists' adjustments to remove that urban heat contamination.
To check how well those particular adjustments work, NOAA set up a network of pristinely located temperature stations across the USA that they could use as a reference. The authors of the study explain:
To help resolve uncertainties caused by reliance on the historical network, NOAA began setting up a U.S. Climate Reference Network starting in 2001. The Climate Reference Network includes 114 stations spaced throughout the U.S. that are well sited and away from cities. They have three temperature sensors that measure every two seconds and automatically send in data via satellite uplink. The reference network is intended to give us a good sense of changes in temperatures going forward, largely free from the issues that plagued the historical network.
With more than a decade's worth of this pristine reference data available, the study authors were able to compare it to the raw and adjusted data. The US land temperature adjustments have the biggest impact on the trend from the 1950s to 1990s, because that's when there were changes in the time of day at which the measurements were recorded, and in the technology used to take the temperatures.
The authors found the adjustments don't have any significant effect on the average temperature or warming trend since 2004. Lead author Zeke Hausfather explained,
Over the last decade there are plenty of issues with the raw data, but they tend to roughly cancel out in their trend effects.
The study showed that the averaged raw and adjusted US land temperature data are both very close to the pristine reference data during that period of 20042015.