Warming of the deep oceans, however, would cause thermal expansion of the deep oceans and add to sea level rise [called steric sea level rise]. The authors examined several datasets including satellite altimetry, ARGO floats, and the GRACE gravitometer satellites, and find that the thermal expansion of the deep oceans and contribution to sea level rise is "negligible," and thus, there is no evidence that the alleged "missing heat" "trapped" by greenhouse gases has somehow sunken to the deep oceans. In addition, the "missing heat" is also nowhere to be found in the upper oceans, nor the atmosphere (because in reality it was lost to space as increased outgoing IR radiation over the past 62 years).
The authors find the sea level budget of total sea level rise is "closed" with "negligible" contribution from the deep ocean, thus no warming or thermal expansion from the "missing heat" in the deep ocean can be accounted for:
"...the sea level budget is closed when using the CCI, AVISO and NOAA data. Hence, in these cases, the deep ocean (below 2000 meters) contribution is negligible."Note: see prior Hockey Schtick posts using the GRACE ocean mass + ARGO steric sea level calculation of sea level change described in this paper, as well as this NOAA 2012 calculation of same showing sea level rising at less than half the rate claimed by the IPCC
Excerpts, full paper here
1 Introduction
For the 1993–2010 time span of high-precision satellite altimetry era, the 5th Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) reported that the rate of global mean sea level (GMSL) rise could be explained by the combined 25 effects of land ice melt (50 %), ocean thermal expansion (37 %) and anthropogenic land water storage decrease (13 %) (Church et al., 2013). Over this period, GMSL rise observed by altimeter satellites amounted 3.2 ± 0.4 mm yr−1 , a value only slightly higher than the sum of the contributions (amounting to 2.8 ± 0.5 mm yr−1 ). Although of the same order of magnitude as associated uncertainties, the 0.4 mm yr−1 difference may also reflect missing contributions, e.g., the deep ocean contribution below 700 m 5 depth where the coverage of ocean temperature data before the Argo era is very poor. Estimating the deep ocean warming is an important issue in the context of the current pause reported since the early 2000s in global mean air and sea surface temperature evolution (also called the “hiatus”, e.g., Held, 2013; Trenberth and Fasullo, 2013; Smith, 2013). Different explanations have been proposed to explain the hiatus, ranging from reduced radiative forcing due to prolonged solar minimum, increased aerosols emissions and small numerous volcanic eruptions, changes in stratospheric water vapor, and enhanced heat uptake in the deep ocean, either in the Pacific or Atlantic regions (e.g., Trenberth and Fasullo, 2010, 2013; Hansen et al., 2011; Solomon, 2010; Guemas et al., 2013; Kosaka and Xie, 2013; Balmaseda et al., 2013a; Watanabe et al., 15 2013; England et al., 2014; Chen and Tung, 2014). The deep ocean heat uptake is currently the favored explanation of the hiatus considering that greenhouse gases continue to accumulate at an increasing rate (Peters et al., 2012) and the Earth’s energy imbalance at the top of the atmosphere is still in the range 0.5–1 Wm−2 (e.g., Hansen et al., 2011; Loeb et al., 2012; Trenberth et al., 2014; Allan et al., 2014). However, there are still too few studies dedicated to quantify deep ocean heat uptake. Accurate observations of sea level rise and its components (ocean thermal expansion and ocean mass change) can, in principle, help constraining the deep ocean contribution (e.g., von Schuckmann et al., 2014). In particular satellite altimetry-based GMSL rise corrected for ocean mass change (for example using GRACE space gravimetry data over the oceans) provides estimate of the total (full depth integrated) ocean thermal expansion (or equivalently ocean heat content). Since the year 2005, comparison with observed Argo-based ocean thermal expansion (down to ∼ 2000 m depth) may help quantifying any deep ocean contribution (below 2000 m).
In effect, the sea level budget equation is described as follows:
GMSL = Ocean Mass + Steric sea level (0–2000 m) + Steric sea level (> 2000m) + data errors (1)
Note: see prior Hockey Schtick post using this GRACE ocean mass + ARGO steric sea level calculation of sea level change as well as this NOAA 2012 calculation of same showing sea level rising at less than half the rate claimed by the IPCC
The residual term defined as the difference between observed GMSL and observed 5 estimates of ocean mass and steric sea level down to 2000 m depth (see Eq. 2 below) includes the deep ocean contribution (called “steric sea level (> 2000 m)”):
Residual = GMSL − Ocean mass − Steric sea level (0–2000 m) = Steric sea level (> 2000m) + data errors (2)
Attempts to estimate the deep ocean contribution from the sea level budget approach were performed in two recent studies (Llovel et al., 2014; Dieng et al., 2015). Dieng et al. (2015) considered two periods (2005–2012 and 2003–2012) which correspond to the availability of new observing systems for estimating thermal expansion and ocean mass (nearly full ocean temperature and salinity coverage down to 2000 m from Argo floats and direct ocean mass measurements from GRACE space gravimetry). Time 15 series of satellite altimetry-based sea level (5 different data sets), thermal expansion (8 different products; integration down to 1500 m) and ocean mass (3 products) components were analyzed in order to estimate the residual term of Eq. (2). Llovel et al. (2014) performed a similar study over the 2005–2013 time span but with less data sets. Another attempt concerning this issue is by von Schuckmann et al. (2014). These studies came up to the same conclusion, i.e., the residual term is contaminated by too large data errors to provide any robust deep ocean contribution estimate. Here we build on these previous studies, in particular that from Dieng et al. (2015). We focus on the 2005–2013 time span corresponding to full Argo coverage and compute the steric sea level component integrating the data down to 2000 m. We also include in our analysis the new sea level product from ESA Climate Change Initiative (CCI)project (www.esa-sealevel-cci.org), available up to December 2013. We use the same approach as in Dieng et al. (2015), i.e., we compute the residual time series. The main objective of the present study is to quantify the contributions of errors coming from one or several terms of the sea level budget (GMSL, ocean mass, steric sea level) in the residual time series. This is an important issue to be addressed before trying to estimate any deep ocean contribution.
Ocean Sci. Discuss., 12, 701-734, 2015
www.ocean-sci-discuss.net/12/701/2015/ doi:10.5194/osd-12-701-2015 © Author(s) 2015. This work is distributed under the Creative Commons Attribution 3.0 License. |
Research Article
13 May 2015
Received: 07 April 2015 – Accepted: 22 April 2015 – Published: 13 May 2015Sea level budget over 2005–2013: missing contributions and data errors
1Laboratoire d'Etudes en Géophysique et Océanographie Spatiales – Centre National d'Etudes Spatiales (LEGOS – CNES), Toulouse, France
2Mediterranean Institute of Oceanography (MIO), Université de Toulon, Toulon, France
3Collecte Localisation Satellites (CLS), Ramonville, France
Abstract. Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (> 2000m). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed trend differences in the residuals of the sea level budget can be as large as ~0.55mm yr−1. These trend differences essentially result from the processing of the altimetry data (e.g., choice the geophysical corrections and method of averaging the along-track altimetry data). At short time scale (from sub-seasonal to multi-annual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), indicating that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content.
Citation: Dieng, H. B., Cazenave, A., von Schuckmann, K., Ablain, M., and Meyssignac, B.: Sea level budget over 2005–2013: missing contributions and data errors, Ocean Sci. Discuss., 12, 701-734, doi:10.5194/osd-12-701-2015, 2015.
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