NOAA scientists released a study last week in Science magazine detailing how new updates on observations show there has been no global warming slowdown.
In science we are always looking for more data to validate results. It is a bit like being a detective: the more information you have, the better the case. For global warming it is meteorological stations overland and buoys and ship data over the ocean.
Methods of analysis matter
The NOAA paper shows how updates in marine and land surface data have increased the quality of results. The new study has also shown how the warming trend of the planet has continued to rise in the past 15 years at the same rate as in the late 20th century.
The global warming speed bump emerged from a leveling off of the rise in global surface temperature since 1998 as seen in several sets of observations, including NASA’s Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP), NOAA, and Hadley Center’s Climate Research Unit (HadCRUT). Three new global temperature records have been set: 2005, 2010 and 2014. It also looks like 2015 might even beat out 2014, producing a possible back-to-back set of records not seen since 1997/1998.
The different centers analyzing global data have common data sets for their analysis, but their methods of interpolation and merging of data vary. This is good because the end result is complementary and delivers a more complete picture of global temperature. For instance, the UK Met Office’s HadCRUT4 does not take much of the Arctic into consideration, which affects the magnitude of the observed surface warming. NASA’s GISS model employs satellite data for nighttime city lights to address urban heat island effects.
Updating observations for oceans and land
The NOAA study has updated the observational records in two ways: accounting for the increasing temporal and spatial coverage of buoys as well as observation methods used by ships, and a much larger land observation dataset. The reanalysis came down to addressing the fact that buoys usually measure cooler temperatures than ship readings, so the authors made a correction to buoy sea surface temperature measurements globally with the new Extended Reconstructed Sea Surface Temperature (ERSST) version 4. Additionally, the authors found that some ship measurements using buckets had existed into the present and had not been measuring temperature with engine intake thermometers, so the ship bias correction was extended.
Land surface air temperatures also benefited from impressive advances in coverage with new data being released, effectively doubling the number of stations available. This includes the Arctic, which has warmed at twice the pace of the rest of the planet.
Natural variability can slow global warming
Scientists who have analyzed the NOAA study still argue that the slowdown remains, albeit not nearly as strong as before the data updates. Natural variability continues to be a hot topic regarding the speed bump in global temperatures.
Last year I attended a very interesting session at the American Meteorological Society’s Annual Meeting in which the global warming “slowdown” was being analyzed using observations and modeling. Volcanoes and anthropogenic aerosols were described as possible reasons, as were natural atmospheric patterns.
A recurring theme emerged in the presentations. The oceans played a prominent role in cooling the planet even though more energy was being trapped in the system by heat trapping gases. The influence of the Pacific Ocean has been seen as one of the major components behind the speed bump in the global temperature trend. These natural patterns shift over time, and 2014 saw some record-setting temperatures in the Pacific that contributed to setting a new record in world temperatures.
Perspectives for the near future
The NOAA paper has helped to reshape the global warming slowdown conversation. The “slowdown” theory sparked an incredible amount of climate research that has given us a better understanding of the Earth system. It seems, however, that we did not have the complete picture, as NOAA scientists argue. We are now at a time of “was the slowdown real?” instead of “what caused the slowdown?”
The one thing I have said to peers is that we will undoubtedly need other data centers to confirm (or refute) the results.
John Kennedy, one of the experts working on HadCRU4’s ocean temperatures, responded on what his center was doing: “We’re constantly working with the data, trying to improve our data sets and better understand the past.
“One thing we try and aim for is a degree of independence,” Kennedy argues. “Even if we’re studying the same phenomena or problem, independent approaches can be a good way to bring out the unknown unknowns and push things forwards.”
Kennedy brings up interesting questions worth asking. “Can we reproduce the results? What are the uncertainties in the estimated ship biases? Do we see similar changes relative to other datasets? We’ll be folding these kinds of questions into our ongoing work on the ocean data and that will eventually feed through into HadCRUT.”
It’s true that many of the same data sources are used by all three centers. Gavin Schmidt of NASA GISS said: “We are updating to GHCN 3.3 this month, and will probably switch to ERSSTv4 (as in the NOAA study) in June. However, discussion about appropriate input data is always ongoing.”
The major global temperature analysis centers are all taking into consideration the new results from NOAA. This is the scientific method, searching for more evidence to support a theory.
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