CLIVAR OSC - Day 1 Highlights - Ocean Role in the Climate System
Nestled between the mountains of Laoshan and the warm waters of the Yellow Sea, over 600 scientists from 50 countries gathered for the second CLIVAR Open Science Conference in Qingdao China, the first one occurring over a decade ago. The first day of the conference was hosted by the Qingdao National Laboratory for Marine Science and Technology—a new sprawling campus performing exciting research endeavors—and featured high profile opening remarks from science leaders and political figures in the region and on the international climate science arena.
“The role of the ocean in the climate system appears today more important than ever,” said Guy Brasseur of the World Climate Research Programme. His remarks resonated with the room and was echoed many of the other speakers. The vision of the conference hopes to achieve progress on this concept by shaping ideas to meet emerging challenges, engaging with future generation of scientists, identifying key climate research and stakeholder issues, and developing and strengthening collaborations across nations, disciplines, and career stages.
During the opening keynote, Thomas Stocker of Bern Research Institute and lead of the IPCC Fifth Assessment Report, emphasized that, “We are living in truly exceptional times. And to prepare for these exceptional times, we need the science to plan for the risks and outcomes.” An important part of that research understands how the ocean is an essential contributor in the climate system. Stocker identified four services provided by the ocean: i) taking up heat; ii) taking up water; iii) taking up carbon; and iv) producing food.
The first day plenary talks aligned with the parallel sessions—energy, carbon, and water. When talking about energy, Monika Rhein, University of Bremen, discussed how the ocean contributes to about 93% of the increase in the total energy budget and about a third of that accumulated heat resides below 700m, with much of the heat increase in the Southern Hemisphere. Observing systems¾such as Deep Argo, repeat hydrography, altimeter, and GRACE¾are vital to maintain and extend, which will help improve independent estimates of energy and sea level change. In regards to the global carbon budget, the ocean has absorbed about 2.6 PgC per year (± 0.5), which is 36% of all anthropogenic emissions over the past decade, according to Laurent Bopp from the Institut Pierre-Simon Laplace. One important area for research is the role of the coastal ocean in the carbon budget—the land ocean aquatic continuum—as well as small-scale processes, sinking processes, and bacteria losses. The models are not dynamic on this front, but observations show significant variability for exported matter in the ocean component of the global carbon budget.
Ray Schmitt, Woods Hole Oceanographic Institution, emphasized how important a role the ocean plays in the global water cycle, considering more than three quarters of the global water cycle consists of the annual rainfall and evaporation freshwater exchange between the ocean and atmosphere. Also emphasized, in regards to the global water cycle, was the importance of evaporation minus precipitation. This is seen in the subtropical gyres, which serve as a major exporter of water and changes the salinity content of the ocean. “With climate change, there will be an intensification of the global water cycle,” said Schmitt. Lijing Cheng gave the final plenary talk on the historical ocean heat content estimation and showed the many discrepancies between reanalysis outputs. One of the problems with calculating ocean heat content is that researchers are starting from different baselines: in the Northern Hemisphere there is an older baseline due to the longer observational record as compared to a younger one for the Southern Hemisphere.
Below are some highlights from the parallel sessions.
- Sustained observations from the Argo data provide a near-global analysis of ocean heat content, which when assimilated in a dynamical model can provide a good estimate in tune with observations of the Earth’s energy imbalance from space.
- These new estimates of ocean heat content and their changes show considerable cancellation in the upper 300 m of the ocean¾with 44% of the short-term trend of 0.8 W/m2 (globally) occurring below 700 m depth for 2005-2014.
- An analysis of surface fluxes¾based on consistent two-dimensional distribution of vertical surface temperature with humidity and wind speed¾helps to minimize the impact of sparse sampling in gridded products of surface flux.
- In the global mean energy budget, there is an acceleration of thermosteric sea level that is consistent with enhanced ocean heat uptake, which is concentrated at depths of 100–400 m and is equivalent to an extra net surface heat input of ~0.2 W/m2 in the 2000s compared to the 1990s.
- Surface-forced warming, along with imposed wind changes, drives ocean warming in the ventilated gyres. In higher latitudes, the observed patterns are forced by surface-forced changes in salinity and wind.
- Using ECCO it is found that advection is more important than mixing in setting the spatial patterns of vertical heat exchange in the ocean. The global integral of vertical heat flux shows an upward heat transport in the deep ocean, suggesting an abyssal cooling trend over 1992-2011.
- The subsurface Southern Ocean is warming rapidly and faster than the global ocean average. According to separate forcing experiments with the Canadian Earth System Model this warming is a relative to earlier cooling by volcanic eruptions and aerosols and is driven mainly by the climate response to ozone depletion.
- There is significant decadal variability, larger than the climate signal, in ocean carbon uptake. In the Southern Ocean, seasonal modes of dissolved inorganic carbon are significant, with links to the submesoscale and mesoscale dynamics.
- In regards to the current and future ocean carbon uptake, the role of submesoscale processes, western boundary currents, mode water formation, and eddies are of interest to further the understanding of carbon sequestration.
- On decadal to multidecadal timescales, the pCO2 surface ocean trends are not different than atmosphere.
- Sources of uncertainty in 21st century projects of potential ocean ecosystem stressors include scenario, model, and internal variability of uncertainty, with different drivers for pH, oxygen, net primary production, and sea surface temperature. Scenario uncertainty dominates on the century timescale.
- Correction of model biases for saturation and carbon disequilibrium will improve the global inventory and reduce regional biases.
- Research showed clear evidence of oceanic sources of moisture for flooding events. There is also considerable regional and seasonal variability as to whether rainfall is supplied from land or ocean evaporation sources, including or the monsoon regions. Changes in land use can potentially feedback on ocean variability, such as ENSO.
- The concept of how the “wet getting wetter” was convincing over ocean grid points. Over land, there are still large uncertainties, with no robust change over 70-75% of the area using analysis of both observations and future projections in models.
- In a warmer future, the rate of change with precipitation appears to become smaller, since radiative effects of increased carbon dioxide suppress it.
- Sea surface salinity can be a remarkable predictor of rainfall up to a season ahead in some regions, such as the northeast subtropical North Atlantic leads the Sahel monsoon precipitation.
- Over the last few decades, central and northern Europe has become wetter, but there is a strong seasonality. Europe, in general, exhibits lengthening of both wet and dry spells. And although satellite products are becoming better at quantifying extremes, they are not there yet.
- In the Arctic region, much of the freshwater input to the ocean is caught up in the Beaufort Gyre and then pumped down by Ekman convergence. Future projections show that Arctic freshwater volumes (liquid form) are projected to increase and not expected to reach equilibrium in the 21st century.
The main sessions of the conference are bookended by two events, including an Early Career Scientists Symposium—which was held the Sunday before and will conclude the weekend after the main program—and Panel meetings. For a full listing of the speakers and agenda topics view the Scientific Programme tab.
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