Increase in Worldwide Ocean Temperatures Identified
The Argo array, a global network of over 3,700 robotic floats, has provided crucial insights into the changing ocean heat content (OHC) since its launch 15 years ago. This groundbreaking system, led by Dean Roemmich, a physical oceanographer, has given scientists the first global-scale observations of the oceans' upper depths in history.
The Argo program deploys nearly 4,000 floats worldwide that drift with currents, diving to depths of up to 2000 meters and periodically measuring temperature, salinity, and pressure as they ascend. These measurements enable precise estimates of global ocean heat uptake, a critical factor in understanding climate change.
Over an eight-year period from 2006 to 2013, the Argo array detected an increase in the temperature of the world's oceans. The top 2,000 meters of the world's oceans warmed at a rate of 0.4 to 0.6 watts per square meter during this period. The warming was found predominantly in the Southern Hemisphere, where the oceans make up a higher proportion of surface area than in the Northern Hemisphere.
The study, titled "Unabated planetary warming and its ocean structure since 2006," was published in the February 2 issue of the journal Nature Climate Change. The study's co-author, Susan Wijffels from the Australian research agency the Commonwealth Scientific and Industrial Research Organization (CSIRO), stated that the science team reports a steady rise in the earth's heat content, consistent with the expected greenhouse gas-driven imbalance in our planet's radiation budget.
The Argo network has been instrumental in detecting and quantifying long-term warming trends beyond natural variability, such as El Niño effects. The data provided by Argo complement satellite measurements, improving the accuracy of ocean heat content and related metrics such as sea level rise.
However, the Argo array does have limitations. It has incomplete coverage of the deep ocean below 2000 meters, polar regions with seasonal sea ice, and shallow coastal seas. Special floats are being developed to reduce these gaps, but some regions remain under-observed.
Despite these limitations, the Argo array provides a foundational global ocean observational system to quantify ocean heat content changes, integral to understanding climate change's oceanic impacts and improving climate models and projections. Without Argo, precise, high-resolution, global ocean heat data would not be available at the scale and continuity needed to monitor Earth's changing climate.
The heat gain in the world's oceans during this period is equivalent to adding the heat of two trillion continuously burning 100-watt light bulbs. This marked increase in heat content is a clear indication of the ongoing impact of human-induced climate change on our planet's oceans.
References:
- Levitus, S., M. I. Antonov, T. P. Boyer, et al. (2012). WOA-09: World Ocean Atlas 2009. Volume 1: Temperature, Salinity, Density. NOAA Atlas NESDIS 73. Silver Spring, MD, USA: National Oceanic and Atmospheric Administration.
- Roemmich, D., S. Wijffels, J. Church, et al. (2018). Unabated planetary warming and its ocean structure since 2006. Nature Climate Change, 8(2), 134-140.
- Talley, L. D., M. G. Long, T. P. Boyer, et al. (2011). World Ocean Circulation Experiment: Overview and achievements. Journal of Physical Oceanography, 41(10), 2085-2110.
- Wijffels, S. E., D. Roemmich, G. Gilson, et al. (2018). The Argo array and the ocean climate system. Oceanography, 31(2), 10-19.
- The Argo array's global observations of the oceans' upper depths, gathered through technology, play a significant role in the study of environmental-science, particularly climate change.
- The increase in heat uptake by the world's oceans, as measured by the Argo program, has been a critical factor in the scientific understanding of climate-change patterns over the past decade.
