By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(German text translated/edited by P. Gosselin)
Climate skeptics have been accused over and over again of fabricating the climate warming hiatus of the past 15 years. A poor argument because the hiatus has been established as an area of research on which a number of scientific groups are working.
The latest study on the subject comes from a group of the British Antarctic Survey (Turner et al. 2016) that was published on July 21, 2016, in the journal Nature. It is a study on the warming hiatus of the Antarctic Peninsula. Yes, you heard it correctly – also here it appears there has been a hiatus.
The surprise is justified – as the German media and authorities claim on a regular basis that the Antarctic Peninsula is among the most rapidly warming regions on earth.
For example on the website of the German Environment Office Umweltbundesamtes (UBA) of July 23, 2013:
The climate of Antarctica
Antarctica is the driest and coldest continent on earth. Temperatures reach the freezing point in the west during the warmest month of January, otherwise they are far below the mean temperature of -55°C. Also Antarctica is impacted by global climate change and it is foremost warming at the Antarctic Peninsula more than the rest of the world. […] Only a few areas of the Antarctic Peninsula reach temperatures above the freezing point on a regular basis during the summer. However, it is the Antarctic Peninsula on the west side of the continent that is strongly hit by global climate change. No region on earth is currently warming faster. The temperature data of a research station on the Antarctic Peninsula run by Oak Ridge National Laboratory shows an annual mean warming of up to 2°C over the past 50 years. For the entire continent a warming of about 0.12°C per decade has been shown.”
John Turner and his colleagues of the British Antarctic Survey (BAS) have combined and evaluated the temperature data from various research stations on the Antarctic Peninsula. Using the data it was possible to divide the trend into a warming phase of 1979-1997 and a cooling phase 1999-2014, the latter being the hiatus. The authors even write the result in the title of their Nature study:
Absence of 21st century warming on Antarctic Peninsula consistent with natural variability
Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere1. This warming has contributed to the regional retreat of glaciers2, disintegration of floating ice shelves3 and a ‘greening’ through the expansion in range of various flora4. Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion5, local sea-ice loss6, an increase in westerly winds5, 7, and changes in the strength and location of low–high-latitude atmospheric teleconnections8, 9. Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation.”
Figure: Temperature curve of the Antarctic Peninsula since 1979 (black curve). The red lines depict the linear trends. The gray bars at 1998 mark the trend change from warming to cooling. Source: Turner et al. 2016.
Turner and his colleagues clearly show that a strong natural variability governs on the Antarctic Peninsula and that it goes far beyond the anthropogenic signal. The change from natural warming phases over to cooling phases is a well-known phenomenon that is shown by ice core studies on the climate development over the past 1000 years.
The BAS scientists warn of simplistic views on warming in the late 20th century. In addition to natural variability (ocean cycles) and CO2, here also the ozone hole could have played a role. The main part of the text in the study states:
The recent change in SAT [surface air temperature] trend can be set in a longer-term perspective through examination of regional ice core records. An ice core from James Ross Island, which is close to Marambio station, showed that the region experienced several periods of rapid warming and cooling in the last 1,000 years, and that the warming trend over the last 100 years was ‘highly unusual’, although not unprecedented. However, the period since the late 1970s includes the ozone hole, which is unique in the record.”
The warming rate of the Antarctic Peninsula indeed was high in the late 20th century, however according to ice core measurements, there was a 50-year interval when temperatures rose even faster than 1979-1997:
The Ferrigno ice core from the coast of West Antarctica shows a warming from the 1950s to the early twenty-first century that agrees well with the warming observed at Vernadsky. In the longer term, this record revealed marked decadal variability and, importantly, resolved a 50-year period in the eighteenth century when SATs increased at a faster rate than observed at Vernadsky over the second half of the twentieth century.”
The most important finding of the study: The alleged extraordinarily strong warming of the Antarctic Peninsula in the late 20th century is well within the range of natural fluctuations. The paper states:
Therefore all these studies suggest that the rapid warming on the AP since the 1950s and subsequent cooling since the late-1990s are both within the bounds of the large natural decadalscale climate variability of the region.
Also see the article at t-online by Andreas Lerg.