The global warming hiatus re-examined

A paper in 'Science' erases the global warming hiatus by adjusting ocean temperature data upwards. Is this a legitimate way to make an ugly problem go away?

Reanalyzed global sea surface temperatures (ERSSTv4) causes furor. Credit: NOAA

PHOENIX, Aug. 18, 2015 — A re-analysis of global ocean surface temperatures in a paper published in Science, America’s most prestigious science journal, raises global temperatures after 2004. It fundamentally alters the climate change debate.

Its results and methods have quickly been incorporated into every major surface-based global temperature database, just in time to influence the Paris climate summit in December.

The paper, “Possible artifacts of data biases in the recent global surface warming hiatus,” formally published on June 26, is first authored by Dr. Thomas Karl, director of NOAA’s National Centers for Environmental Information (formerly the National Climate Data Center).

Why is this one paper so important? Why is the recalibration of ocean surface temperatures questioned?

Since 2005, skeptics have pointed out that the rate of increase in global temperatures since 1997 has dropped to near zero, even though human CO2 emissions have risen fully 25 percent and are at their highest levels ever. Skeptics dubbed the slowdown “the pause.”

For about a decade, human-caused global warming (AGW) theorists denied that a slowdown in warming had occurred. AGW theorists correctly argued that it would take at least a decade for any slowdown documented in the temperature record to become statistically significant.

Finally, in late 2013, the International Panel on Climate Change (IPCC) acknowledged the existence of the pause, renaming it a “hiatus” from global warming. Since then, at least 50 papers have appeared in the scientific literature explaining where the missing heat went.

The existence of a 17-year, unanticipated “hiatus” in the face of rapidly increasing CO2 emissions is jeopardizing the AGW theory. Fifty different concocted explanations for the unexpected, unpredicted disappearance of warming doesn’t help.

Reanalyzed sea surface temperatures vs. previous record. Credit: Steve Davidson/NOAA data)
Reanalyzed sea surface temperatures vs. previous record. Credit: Steve Davidson/NOAA data

In steps Karl to the rescue. He and his co-authors reanalyzed the Extended Reconstructed Sea Surface Temperature (ERSSTv4) dataset. Seventy percent of earth’s surface and 90 percent of its surface heat are tied to oceans.

The graph above compares the re-analyzed dataset with the previous version (ERSSTv3b). The re-analyzed version creates global warming after 2004 where little had previously existed. In one fell swoop, the “hiatus” just disappears.

Argo array of active floats, color coded by country, as of April 2015. Credit: Wikipedia
Argo array of active floats, color coded by country, as of April 2015. Credit: Wikipedia

The main reason for that is that Karl added 0.12°C to all Argo buoy temperature readings and gave them added weighting when calculating the re-analyzed dataset, according to a critique of Karl’s paper by Dr. Ross McKitrick.

The Argo array and ship-based temperature measurements are in disagreement. Argo’s temperatures are colder than ship-based temperatures and show no sea surface temperature increases since its earliest measurements began. Karl’s change to Argo data increases global temperatures after 2004, when Argo buoys started showing up in large numbers. The Argo network went fully operational in late 2007 with 3,000 floats in place.

The international Argo array is a wonder of modern climate science technology. It consists of nearly 3,900 specially designed buoys distributed in oceans all over the world. Each self-contained robotic buoy records ocean temperature, salinity and ocean drift to a depth of 6,500 feet. They normally free float at 3,000 feet. Every 10 days they dive and then return to the surface, taking measurements all along the way. Once surfaced, they automatically upload their collected data via satellite into a global database.

Argo is specifically designed for climate science. Ship-based measurements are not. Ships have taken measurements in many different ways over the years. Most modern-day water temperature readings from ships are taken from boiler room water intakes not designed for rigorous scientific purposes. Those have a built-in heat bias.

Instead of logically recalibrating the less reliable ship-based data to match the Argo data, Karl alters the Argo data to match the ship-based measurements.

It’s hard to see visually in the above ERSST comparison, but trend analysis shows older temperature data — before 1976 — were adjusted slightly downward, while data were adjusted upward after 2004 in the re-analysis. Measurements after 1976 are also adjusted upward. That conveniently increases the slope of global warming in favor of AGW theory.

The Karl paper came out in June. In less than two months, its results and methods have been incorporated into virtually all major ground-based global temperature databases.

The Argo array itself shows no warming since 1997. Satellite-based global sea surface data, unaffected by Karl’s results, show no warming in the lower troposphere since 1997. They all support the existence of the hiatus.

Clearly, either Argo and the satellites are wrong, or Karl’s re-analysis is wrong. The hiatus is either real or it is not.

This much is certain, though: The science is not settled.

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