Decadal Climate Predictions in the North Atlantic Region

The Role of Ocean Heat Transport

International Max Planck Research School on Earth System Modelling

Sprache:

Leonard Friedrich Borchert

Leonard Borchert ist Klimaforscher mit vielschichtigen inhaltlichen Interessen. Nach Forschungsschwerpunkten in Küstendynamik und ökonomischen Auswirkungen des Klimawandels untersucht er seit 2015 die Vorhersagbarkeit europäischer Oberfchentemperaturen bis zu 10 Jahre in die Zukunft. Zudem engagiert er sich in diversen Netzwerken für die Rechte Promovierender in Deutschland.

Auf einen?

Expertise

  • Climate dynamics
  • Climate prediction
  • Science politics

 

Interessant für

  • Environment NGOs
  • Consultancies
  • Reinsurers
  • Climate enthusiasts
Lena Bell/Unsplash
Leonard Friedrich Borchert

Leonard Borchert ist Klimaforscher mit vielschichtigen inhaltlichen Interessen. Nach Forschungsschwerpunkten in Küstendynamik und ökonomischen Auswirkungen des Klimawandels untersucht er seit 2015 die Vorhersagbarkeit europäischer Oberfchentemperaturen bis zu 10 Jahre in die Zukunft. Zudem engagiert er sich in diversen Netzwerken für die Rechte Promovierender in Deutschland.

Auf einen?

Expertise

  • Climate dynamics
  • Climate prediction
  • Science politics

 

Interessant für

  • Environment NGOs
  • Consultancies
  • Reinsurers
  • Climate enthusiasts

Interview

Anja Zeltner
Freie Autorin

Is it possible to predict the climate reliably several years in the future?

Leonard Friedrich Borchert
schreibt…
Anja Zeltner
Freie Autorin

Is it possible to predict the climate reliably several years in the future?

Leonard Friedrich Borchert
Gastautor

This depends on the specific location and target variable: For example, most current climate models cannot predict precipitation accurately on this time scale. In general, current climate models predict relatively well if weather conditions will be warmer or cooler in the next ten years if they take into account what the climate condition was at the beginning of the prediction. The forecast of exact temperatures does not work that well. Studies that simulate predictions in the last 60 years and compare these with actual observations have found that these decadal climate predictions work particularly well in the North Atlantic region.

Anja Zeltner
Freie Autorin

How do the predictions work that you analyse in your thesis?

Leonard Friedrich Borchert
Gastautor

Here, the demarcation to climate projections is very important: The predictions I deal with are generally less reliable than climate change scenarios. The reason for this is that for the decadal time scale there is more to take into account than the increase of greenhouse gas concentrations in the atmosphere, for example, like with weather forecasts, the condition of the climate system at the beginning of the prediction. In my thesis, I analysed why surface temperatures of the North Atlantic region are so well predictable up to ten years. I found out that the oceanic transport of heat into the North Atlantic plays an important role for the reliability of temperature forecasts there.

Anja Zeltner
Freie Autorin

In your time as a PhD student and until now, you have been involved in various PhD networks. What do you think about the situation for PhD students in Germany right now?

Leonard Friedrich Borchert
Gastautor

In the last years, many things have improved. For example, many academic organisations have abolished scholarships and introduced supervision panels, groups of researchers that supervise single PhD students. Many PhD students are now well insured during their PhD studies, but this is unfortunately not the case for PhD students with scholarships. Also, the risk for abuse of power through single supervisors has diminished through the panel system. Still, there are many things left to be done: PhD students often do not receive full payment for full-time work, they are often physically and psychically challenged through stress, and despite supervision panels, abuse of power still exists. But there is hope: I am again and again impressed by the work of self-organised groups of PhD students, for example, the N2 network where I am also active.

Keywords

Ocean Heat Transport, Decadal Climate Prediction, North Atlantic, AMOC, Climate Modelling

Summary

The possibility of credible climate forecasts for several years ahead – on the decadal time scale – has received considerable public and economic attention. Scientific studies quantify the credibility of such forecasts by evaluating the average predictive quality (skill) over the last 50-60 years (in so-called hindcasts). Decadal hindcasts of surface temperatures were shown to be on average particularly skillful in the North Atlantic region. However, the reason for the high skill of these hindcasts is still unclear. Meanwhile, North Atlantic sea surface temperatures (SSTs) are on the decadal time scale strongly influenced by subpolar ocean heat transport (OHT) variability. I here connect OHT variability and SST predictability and test whether the knowledge of the strength
of subpolar OHT at the beginning of a single SST forecast can improve its credibility. By using initialized global climate simulations of the twentieth century, I confirm previous studies in that OHT variability influences SST variability for 3–10 years. A characteristic SST pattern of warm anomalies in the northeast Atlantic and cold anomalies in the Gulf Stream region emerges after strong OHT phases and vice versa. This pattern originates from persistently growing upper ocean heat content anomalies that arise from Southward propagating OHT anomalies in the North Atlantic. Extending previous work, I analyze strong and weak OHT phases at 50◦N separately. This reveals an asymmetry between strong and weak phases of ocean heat transport: When subpolar OHT is strong, North Atlantic SSTs show stronger and more persistent decadal anomalies than when subpolar OHT is weak.
For the first time, I show that the hindcast skill of northeast Atlantic SSTs 3–10 years ahead is linked to the characteristic SST pattern, and therefore OHT variability in the subpolar North Atlantic. When subpolar ocean heat transport is strong at the initialization of a hindcast, the skill of SST hindcasts in the northeast Atlantic 2 to 9 years into the future is significantly higher than when the ocean heat transport is weak at initialization. The asymmetric effect of strong and weak phases of subpolar OHT on SST variability that preconditions asymmetric hindcast skill is robust in non-initialized versions of the same climate model. The skill of decadal SST predictions, therefore, robustly depends on the climate state at the start of a prediction.
I show in this dissertation that hindcast skill changes over time and thus cannot be immediately translated into the credibility of a forecast. Instead, the credibility of a decadal climate forecast depends on the climate state at the start of the forecast. For North Atlantic SST forecasts, the strength of subpolar North Atlantic OHT at the start of the forecast can be used to estimate its credibility. Findings presented in this dissertation suggest that physical mechanisms might be used to improve conventional estimates of the credibility of a climate forecast on the economically and politically relevant decadal time scale.

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Zitiervorschlag

Borchert, Leonard. Decadal Climate Predictions in the North Atlantic Region: The Role of Ocean Heat Transport. Universität Hamburg, 2018, doi:10.17617/2.2639896.

Repository

pure.mpg.de

Identifikatoren

urn: urn:nbn:de:gbv:18-92756

doi: 10.17617/2.2639896

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