Abstract
AbstractLack of reliable observational metadata represents a key barrier to understanding sea surface temperature (SST) measurement biases, a large contributor to uncertainty in the global surface record. We present a method to identify SST measurement practice by comparing the observed SST diurnal cycle from individual ships with a reference from drifting buoys under similar conditions of wind and solar radiation. Compared to existing estimates, we found a larger number of engine room‐intake (ERI) reports post–World War II and in the period 1960–1980. Differences in the inferred mixture of observations lead to a systematic warmer shift of the bias adjusted SST anomalies from 1980 compared to previous estimates, while reducing the ensemble spread. Changes in mean field differences between bucket and ERI SST anomalies in the Northern Hemisphere over the period 1955–1995 could be as large as 0.5°C and are not well reproduced by current bias adjustment models.
Highlights
Sea surface temperature (SST) is a crucial parameter for climate change assessments (Hartmann et al, 2013) but its uncertainty affects our confidence in estimates of surface-temperature change
We found a larger number of engine room-intake (ERI) reports post–World War II and in the period 1960–1980
For more than 75% of the observations, we could diagnose the measurement method from the diurnal anomalies without relying on SST method indicator (SI)(M), higher percentages of unclassified observations are present at the beginning of the record and during World War II (WWII)
Summary
Sea surface temperature (SST) is a crucial parameter for climate change assessments (Hartmann et al, 2013) but its uncertainty affects our confidence in estimates of surface-temperature change. Typical atmospheric conditions over the ocean combine to produce a global mean cool bias relative to the true SST, ranging from about À0.1°C in 1850s to À0.4°C in 1940s (Folland & Parker, 1995; Smith & Reynolds, 2002). This increase in bias is due to changing bucket types, from wooden to canvas, and increasing ship speed (e.g., Kennedy et al, 2011b, hereafter K11b) and increasing airflow past the buckets.
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