Correcting datasets leads to more homogeneous early-twentieth-century sea surface warming

Abstract

Existing estimates of sea surface temperatures (SSTs) indicate that, during the early twentieth century, the North Atlantic and Northeast Pacific oceans warmed by twice the global average, whereas the Northwest Pacific Ocean cooled by a magnitude equal to the global average 1-4 . Such a heterogeneous pattern suggests first-order contributions from regional variations in forcing or in ocean-atmosphere heat fluxes 5,6 . These older SST estimates are, however, derived from measurements of water temperatures in ship-board buckets, and must be corrected for substantial biases 7-9 . Here we show that correcting for offsets among groups of bucket measurements leads to SST variations that better correlate with nearby land temperatures and are more homogeneous in their pattern of warming. Offsets are identified by systematically comparing nearby proximal SST observations among different groups 10 . Correcting for offsets in German measurements decreases warming rates in the North Atlantic, whereas correcting for Japanese offsets leads to increased and more uniform warming in the North Pacific. Japanese offsets in the 1930s primarily result from records having been truncated to whole-degrees Celsius when digitized in the 1960s. These findings underscore the fact that historical SST records reflect both physical and social dimensions, and suggest that further opportunities exist for improving the accuracy of historical SST records 9,11 .

Ocean Acidification Has Impacted Coral Growth on the Great Barrier Reef

“…It is likely that well‐documented uncertainties in the historical temperature data products during this time period (e.g., Chelton & Risien, 2016) confound our estimation of the temperature effects on Porites density and caused the ~4% decline in density around 1940 that we currently attribute to OA. Efforts to increase the accuracy of the historical temperature records (e.g., Chan et al, 2019) will improve our estimates of the OA impact on coral skeletal growth. Overall, however, the model‐predicted effects of extension and temperature on skeletal density are in good agreement with the independently measured density changes (Figures 3a and 3b), and our results indicate strong impacts of OA on GBR corals post‐1950.…”

The early 20th century warming: Anomalies, causes, and consequences

“…A truly global average of temperature would in addition be affected by missing data, particularly in the Arctic (Karl et al, ). Even fairly recently, an inhomogeneity of SST data, caused by changing contributions by different shipping fleets, has been detected and corrected (Kennedy et al, ), while other inhomogeneities are likely still present, which may lead to an overestimate of the unforced component of the ETCW (Chan & Huybers, n.d.). In addition, there are remaining biases in land temperature data, such as summer temperature biases preceding the widespread use of the Stevenson screen (Auchmann & Brönnimann, ; Brunet et al, ) which may lead to an overestimation of summer temperatures prior to the second half of the 20th century.…”

Multi-year ocean thermal variability

“…Upper ocean variability over decades is comparatively well-observed, including the ENSO cycle, and sea surface temperatures, although problems persist (e.g. Chan et al, 2019). For the heat uptake estimation context, see the reviews by Abraham et al (2013) or Meyssignac et al (2019).…”