Measuring Global Ocean Heat Content from space to monitor the Earth Energy Imbalance
Abstract
The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4-1 Wm$ ^{-2}$). This imbalance is coined Earth's Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gas emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 90% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat such that the monitoring of Ocean Heat Content (OHC) and its long-term change provides a precise estimate of EEI. Today, global OHC changes can be tracked from space with a combination of the altimetric measurement of sea level change and the gravimetric measurement of ocean mass change. In this talk we review this current space method to estimate global OHC changes and evaluate its relevance to derive EEI estimates on different time scales. We compare its performance with three state-of-the-art methods to estimate global OHC changes based respectively on: (1) direct observations of in situ temperature; (2) satellite-based measurements of the ocean surface net heat fluxes and (3) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. We find that achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E..21M