Universität Bristol fordert IPCC auf, Ozeanzyklen bei Temperaturprognosen stärker miteinzubeziehen

Schon bald beginnen Klimawissenschaftler mit den Arbeiten zum 6. IPCC Klimazustandsbericht. Es ist klar, dass sich einiges ändern muss. So mahnte die University of Bristol am 9. November 2016 eine stärkere Berücksichtigung der Ozeanzyklen bei den Temperaturprognosen an:

Experts call on international climate change panel to better reflect ocean variability in their projections

Ocean variability and realistic marine regional projections should be included in Intergovernmental Panel on Climate Change (IPCC) reports to better inform policy-makers, state researchers from the University of Bristol and University of Tasmania.

A commentary on what should be included in the next IPCC special interdisciplinary report on oceans and the cryosphere has been released today in Nature by Daniela Schmidt, Professor of Palaeobiology from the University of Bristol and Philip Boyd, a professor of marine biogeochemistry from the Institute for Marine and Antarctic Studies, University of Tasmania. The IPCC is an international body which was set up in 1988 to assess the science related to climate change. Currently on its sixth assessment cycle, the goal of the IPCC is to inform policymakers of the science on climate change, the impacts, future risks and potential options for adaption and mitigation.

The latest IPCC report had for the first time chapters dedicated to the Oceans. This year, the IPCC are going one step further with a special interdisciplinary report on the ocean and the cryosphere which will be published in 2019. In December, a panel of experts will discuss what should be included in this special report. Professors Schmidt and Boyd think that changes need to happen in three key areas:

  • The first area to consider is ocean variability. Current climate change projections are based on global averages, but in reality ocean data is extremely noisy due to local, regional and global variability. Therefore projections need to incorporate ocean variability, especially when natural climate variability currently has the potential to temporarily offset and or amplify trends driven by anthropogenic climate change
  • Another area to consider is moving projections from the global to the regional scale, and where possible to local scales. This is most important for effectively managing marine resources.  The current regional projections created from global climate models don’t always agree and ignore human stressors such as fishing. Regional and local stressors, along with local know-how, need to be incorporated to fully-inform policymakers on how local marine ecosystems and services will be affected by climate change
  • A final area to consider is how marine organisms will be affected by climate change. Our knowledge is based on experiments on individual species, often not considering multiple factors all acting at the same time and place. Research, therefore, needs to be designed to incorporate multiple and variable stressors and lead to fundamental understanding how these organisms react to climate change and ocean acidification. Researchers should also consider the effect of fluctuating and extreme conditions on an organism’s physiology. This will help gain a better insight into how marine organisms will face a changing and variable ocean.

Professor Schmidt said: “IPCC projections are focussed on the mean state of change in the year 2100. Governments have accepted that climate change is happening. However, global action takes years to be negotiated while local action can be much faster implemented and really have an impact.” Professor Boyd added: “A series of interim projections, on the joint effects of anthropogenic climate change and natural variability, on a decadal or shorter timescale would provide invaluable touchstones for marine resource managers. “Ultimately, the IPCC needs to shift their approach. The talks in December must acknowledge the variability of the oceans whilst focussing more on the effect of regional scale pressures to aid in creating practical policy solutions of the future.”

Paper: ‘Forecast ocean variability’ by Daniela Schmidt and Philip Boyd in Nature

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Eine Woche später erschien zum selben Thema ein Übersichtsartikel von Riccardo Farneti in WIREs Climate Change, in dem er Möglichkeiten der Modellierung unter Zuhilfenahme von Ozeanzyklen vorstellt:

Modelling interdecadal climate variability and the role of the ocean
To estimate the anthropogenic contribution to climate signals in the recent past and future decades implies a certain degree of confidence in both understanding and simulating natural internal variability at interdecadal time scales. If we are to embark on the challenge of decadal prediction, we must be able to mechanistically attribute events to known processes and phenomena, and reproduce their features and statistics within our models. To date, models have succeeded in reproducing only partially spatial patterns, statistics and climatic impacts of interdecadal modes of variability. Reasons for the partial success and agreement among models are to be attributed to the short observational record, the different and complex flavours of coupling between the many subcomponents of the climate system, and the present inability to resolve all climate processes. At an even more fundamental level, this difficulty is aggravated by the limited understanding of the physical mechanisms involved. Here, we review the proposed mechanisms giving rise to interdecadal climate variability, we discuss the hypotheses explaining the main interdecadal modes of variability, and present an overview on the ability and level of agreement in their simulation by the latest generation of coupled climate models. To achieve any progress, the modeling community should focus on both improving the representation and parameterization of key ocean physical processes and obtaining a firmer grasp on the physical mechanisms generating the variability. Both goals can benefit from process studies, intercomparisons with perturbation experiments to study model’s sensitivities, and the use of a hierarchy of climate models.

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Wir nutzen die Gelegenheit, Ihnen weitere aktuelle Fachliteratur zum Thema Ozeanzyklen vorzustellen. Am 31. Juli 2015 erschien das folgende Paper eines Teams um Veronica Nieves in Science, das die fehlende Erwärmung der letzten anderthalb Jahrzehnte mit den Ozeanzyklen und verschiedenen Tiefenstockwerken der Wassersäule in Verbindung bringt:

Recent hiatus caused by decadal shift in Indo-Pacific heating
Recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature warming in the most recent decade. Some of these studies seem to support the idea of internal variability and/or rearrangement of heat between the surface and the ocean interior. Others suggest that radiative forcing might also play a role. Our examination of observational data over the past two decades shows some significant differences when compared to model results from reanalyses and provides the most definitive explanation of how the heat was redistributed. We find that cooling in the top 100-meter layer of the Pacific Ocean was mainly compensated for by warming in the 100- to 300-meter layer of the Indian and Pacific Oceans in the past decade since 2003.

Judith Curry kommentierte das Paper in ihrem Blog:

This paper is important in clarifying the vertical and horizontal distribution of subsurface temperature changes in the ocean.  And I am particularly glad to be reminded of the OI SST data set, which may be the best SST data set to use for recent decades.  The hiatus clearly lives, both in upper ocean heat content and surface temperatures from OI SST data set.

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Hier noch ein Artikel zu den Atlantischen Klimazyklen aus dem Dezember 2014 von Jacques Servain und Kollegen in Climate Dynamics:

Recent climatic trends in the tropical Atlantic
A homogeneous monthly data set of sea surface temperature (SST) and pseudo wind stress based on in situ observations is used to investigate the climatic trends over the tropical Atlantic during the last five decades (1964–2012). After a decrease of SST by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial (>1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Surprisingly, the trade wind system also strengthened over the peirod 1964–2012. Complementary information extracted from other observational data sources confirms the simultaneity of SST warming and the strengthening of the surface winds. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing. Conversely, we suggest that long-term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the Atlantic meridional overtuning circulation and the subtropical cells are required to explain the observations.