Has global warming data been “rigged” to “fit in with climate change fiction”?

Since 2014, climate change deniers have hurry millions of views, Facebook shares and Twitter retweets by telling a story alleging the discovery of “fake” NASA data designed to “fit a climate change narrative”. Although copied almost wholesale from a blog post, the most successful version of the story online was published on the one-stop conspiracy theory/supplement store called Natural News. The article suggested:

In what may be the biggest science fraud ever uncovered, NASA and NOAA have been caught red-handed altering historical temperature data to produce a “climate change narrative” that defies reality. […] We now know that historical temperature data for the continental United States was deliberately altered by NASA and NOAA scientists in a politically motivated attempt to rewrite history and claim that global warming is driving a trend to rising US temperatures.

There’s a lot to unpack here, but the first thing you need to know is that global surface temperature records are constantly refined based on the addition of new data, new statistical analysis or new historical information about the history of a specific data source. To report such a change as something to be “discovered” betrays a potentially willful ignorance of how climate science works. These changes are made public, based on established scientific criteria, and subject to rigorous internal and external peer review.

Where does this come from?

The “smoking gun” relates to a climate record known as NASA’s Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP). These records are based on a massive global dataset of temperature stations around the world, combining multiple data collections originally collected by individual weather stations. The record provides “a measure of global surface temperature change with monthly resolution for the period since 1880, when a reasonably global distribution of weather stations was established.”

To make the case for “fake” data evidence, Natural News, along with the original blog post, highlighted a version of the GISTEMP record for the US first published in 1999, comparing it to the one released later, in 2012. The record, these sources point out, has changed:

(Those graphics plot how much the average temperature of the United States of each year differs from the average temperature for the entire period 1951-1980; the frame labeled “a” is from 1999.)

It should come as no surprise that the data changed after 1999, as shown graphically in the diagram above, as NASA released many papers in 1999 and 2001 about these changes and why they were made. Links to these documents can be found on the NASA website, which abstract changes in several other places.

Why adjust climate data?

Writing for climate news website Skeptical Science, research scientist at Berkeley Earth Zeke Hausfatherwhose work (partly) independently analyzes the adjustments made by government agencies’ climate records, Explain the need to make adjustments to these datasets in general. A main misconception, he argues, is that an “unadjusted global temperature record” – which must necessarily take into account not only the temperature reading at a given recording station, but also how to translate these data in space to arrive at a single annual statement. or monthly issue – isn’t really a thing that exists to begin with:

There are a number of people who question the need for adjustments. Why not just use raw temperatures, they ask, since these are pure and unmixed? The problem is… there really is no such thing as a pure, unaltered temperature record. Temperature stations in the United States are operated primarily by volunteer observers (the Network of cooperative observers, or cooperative stations for short). Many of these stations were set up in the late 1800s and early 1900s as part of a nationwide network of weather stations, focused on measuring daily weather changes rather than decadal changes in climate.

Almost every station on the network’s network has been moved at least once in the last century, with many having 3 or more separate moves. Most stations have changed [the type of instruments used]. Observation hours have changed from afternoon to morning at most stations since 1960, as part of a National Weather Service effort to improve precipitation measurements.

So what are the issues that led to changes between the 1999 record and the last one? According to on NASA’s GISTEMP website, “Starting in the 1990s, the methodology took into account documented nonclimate biases in the raw data and eliminated or corrected for unrealistic outliers.” The purpose of these adjustments is to remove poor quality data from the data set using pre-established methodologies, not to accommodate a “climate change discourse”.

These “non-climate biases” include things like stations taking temperature measurements at different times of the day, stations physically moving (sometimes at a different altitude), and other artifacts that produce changes in a non-climate record. attributable to climate or weather. These non-climate biases were identified and their method of adjustment described in a publicly available 2001 paper found, among other places, on the NASA website. They included:

  • Observation time: Not all stations collect observations at the same time, and some stations, especially in the United States, have changed the time at which data is collected over time. Correcting for these effects is the most significant adjustment made to the GISTEMP dataset after 1999.
  • Station location history: Sometimes stations move to another location, which affects the recording. Archives after 1999 take this into account.
  • Change of thermometer type: A definite change in the data came from the change from liquid-in-glass thermometers to the maximum-minimum temperature system (MMTS). Archives after 1999 take this into account.
  • Urban heat effect: Densely populated urban areas retain more heat than rural areas. An increase in stations in urban areas over time, for example, would create a false warming trend. Archives after 1999 also take this into account.

Additionally, GISTEMP records after 1999 use models to fill in areas with missing data to create a more spatially complete record. The methods used and their effect on the data are all disclosed online. However, the issues described above are largely moot as of this writing in 2019. The GISTEMP analyzes in question above relate to a formulation of the dataset (GISTEMP v3) that has been replaced by a model improved named GISTEMP v4which includes a much larger data set and a whole different set of adjustments.

“Caught red-handed”

Altogether, the most significant effect of all these changes came from time of day adjustments. Collectively, the adjustments served to produce a slight increase warming trend in the United States record from previous records.

The most significant adjustments are the observation time adjustment and the station history adjustment, each of which increases the average warming in the United States by about 0.15°C over the past few years. 100 years. The net result of the five adjustments to the … record is a warming of about 0.3ºC

To suggest – 14 years after the fact – that identifying publicly discussed adjustments to raw data whose methods have been published in peer-reviewed journals is tantamount to catching scientists “in the act” in “the biggest scientific fraud ever discovery” reveals only the ignorance of the author, not an infamous sleight of hand by climatologists. As such, the allegation is rated “False”.

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