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Recent Cooling of the Upper Ocean
John M. Lyman1,2,3, Josh K. Willis4, and Gr egory C. Johnson1
Submitted 26 May 2006
to
Geophysical Resear ch Letters
Accepted 31 July 2006
Published 20 September 2006
Abstract.
"We observe a net loss of 3.2 (± 1.1) × 1022 J of heat from the upper ocean between 2003 and 2005. Using a broad array of in situ ocean measurements, we present annual estimates of global upper-ocean heat content anomaly from 1993 through 2005.
Including the recent downturn, the average warming rate for the entire 13-year period is
0.33 ± 0.23 W/m2 (of the Earth's total surface area). A new estimate of sampling error in the heat content record suggests that both the recent and previous global cooling events are significant and unlikely to be artifacts of inadequate ocean sampling.
1. Introduction
With over 1000 times the heat capacity of the atmosphere, the World Ocean is the
largest repository for changes in global heat content [Levitus et al., 2005]. Monitoring
ocean heat content is therefore fundamental to detecting and understanding changes in the
Earth’s heat balance. Past estimates of the global integral of ocean heat content anomaly
(OHCA) indicate an increase of 14.5 × 1022 J from 1955 to 1998 from the surface to 3000
m [Levitus et al., 2005] and 9.2 (± 1.3) × 1022 J from 1993 to 2003 in the upper (0 – 750
m) ocean [Willis et al. 2004]. These increases provide strong evidence of global
warming. Climate models exhibit similar rates of ocean warming, but only when forced
by anthropogenic influences [Gregory et al., 2004; Barnett et al., 2005; Church et al.,
2005; Hansen et al., 2005].
While there has been a general increase in the global integral of OHCA during the
last half century, there have also been substantial decadal fluctuations, including a short
period of rapid cooling (6 × 1022 J of heat lost in the 0–700 m layer) from 1980 to 1983
[Levitus et al., 2005]. Most climate models, however, do not contain unforced decadal
variability of this magnitude [Gregory et al., 2004; Barnett et al., 2005, their Figure S1;
Church et al., 2005; and Hansen et al., 2005] and it has been suggested that such
fluctuations in the observational record may be due to inadequate sampling of ocean
temperatures [Gregory et al., 2004]. We have detected a new cooling event that began in
2003 and is comparable in magnitude to the one in the early 1980s. Using highresolution
satellite data to estimate sampling error, we find that both the recent event and
the cooling of the early 1980s are significant with respect to these errors."
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