Despite the fact that average temperatures on land have been increasing from year to year, globally averaged surface temperatures from 2000 to 2010 have shown only moderate warming. This is because sea surface temperatures over the past decade have been flat, if not slightly decreasing. In light of this, scientists are curious about whether this reduced rate of surface warming indicates a reduction of the accumulation of heat in the Earth system over the same period.
Palmer et al. use multicentury climate model simulations to study the relationships among decadal trends in top-of-atmosphere radiation balance (which controls the heat content of the Earth system), ocean heat content, and surface temperature. Consistent with previous studies, they find that all models show large variability in sea surface temperature (SST). This large internal variability in SST could easily “mask the anthropogenic warming signal for a decade or more,” the authors note. By contrast, ocean heat content more closely tracks the radiation budget at the top of the atmosphere, suggesting that measurements of ocean heat to deeper levels would help us monitor climate change more accurately.
Source: Geophysical Research Letters, doi:10.1029/2011GL047835, 2011 http://dx.doi.org/10.1029/2011GL047835
Title: Importance of the deep ocean for estimating decadal changes in Earth’s radiation balance
Authors: Matthew D. Palmer, Douglas J. McNeall and Nick J. Dunstone: Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, United Kingdom.
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L13707, 5 PP., 2011
Importance of the deep ocean for estimating decadal changes in Earth’s radiation balance
- Decadal trends in SST place only weak constraint on TOA
- As we measure OHC deeper, we gain increasingly good predictions of TOA
- Trade-off between measuring longer or deeper for given uncertainty in TOA
We use control run data from three Met Office Hadley Centre climate models to investigate the relationship between: net top-of-atmosphere radiation balance (TOA), globally averaged sea surface temperature (SST); and globally averaged ocean heat content (OHC) on decadal timescales. All three models show substantial decadal variability in SST, which could easily mask the long-term warming associated with anthropogenic climate change over a decade. Regression analyses are used to estimate the uncertainty of TOA, given the trend in SST or OHC over the same period. We show that decadal trends in SST are only weakly indicative of changes in TOA. Trends in total OHC strongly constrain TOA, since the ocean is the primary heat store in the Earth System. Integrating OHC over increasing model levels, provides an increasingly good indication of TOA changes. To achieve a given accuracy in TOA estimated from OHC we find that there is a trade-off between measuring for longer or deeper. Our model results suggest that there is potential for substantial improvement in our ability to monitor Earth’s radiation balance by more comprehensive observation of the global ocean.