On the Interpretation of Climate Change in the Tropical Pacific

Analysis of sea surface temperature (SST) observations of the last 150 years reveals strong changes in the tropical Pacific climate system during the most recent decades. These changes can be best described as a slow variation of the mean state of the tropical Pacific. The superimposed interannual variability associated with the El Niño/Southern Oscillation (ENSO) phenomenon does not exhibit any significant changes. However, the change in the mean state is “El Niño-like”, with many aspects observed during present-day El Niño events. Thus, the change in the mean state biasses the SSTs in the tropical Pacific towards the warm side, which explains the stronger and more frequent El Niños observed during the recent decades

Tropical Pacific influences on the North Atlantic thermohaline circulation

Most global climate models simulate a weakening of the North Atlantic Thermohaline Circulation (THC) in response to enhanced greenhouse warming. Both surface warming and freshening in high latitudes, the so-called sinking region, contribute to the weakening of the THC. Some models simulate even a complete breakdown of the THC at sufficiently strong forcing. Here results from a state-of-the-art global climate model are presented that does not simulate a weakening of the THC in response to greenhouse warming. Large-scale air-sea interactions in the tropics, similar to those operating during present-day El Niños, lead to anomalously high salinities in the tropical Atlantic. These are advected into the sinking region, thereby increasing the surface density and compensating the effects of the local warming and freshening. The results of the model study are corroborated by the analysis of observations

El Hermanito: El Niño's overlooked little brother in the Atlantic

An oscillation with a period of about 30 months has been identified in the equatorial Atlantic by analyzing sea surface temperature (SST) observations for the period 1949-1991. The 30-month time scale was also found in numerical simulations with an atmospheric general circulation model (AGCM) that was forced by these SSTs and a coupled ocean atmosphere general circulation model (CGCM). Consistent with the theory of tropical air-sea interactions, the Atlantic oscillation (El Hermanito) is an inherently coupled air-sea mode and can be viewed as the Atlantic analogon of the El Nino/Southern Oscillation (ENSO) phenomenon in the equatorial Pacific. El Hermanito is an internal Atlantic mode and appears to be independent of the quasi-biennial (QB) variability observed in the tropical Indian and Pacific Oceans. The discovery of El Hermanito is important to the prediction of Atlantic climate anomalies. (orig.

Influence of the Multidecadal Atlantic Meridional Overturning Circulation Variability on European Climate

The influence of the natural multidecadal variability of the Atlantic meridional overturning circulation (MOC) on European climate is investigated using a simulation with the coupled atmosphere–ocean general circulation model ECHAM5/Max Planck Institute Ocean Model (MPI-OM). The results show that Atlantic MOC fluctuations, which go along with changes in the northward heat transport, in turn affect European climate. Additionally, ensemble predictability experiments with ECHAM5/MPI-OM show that the probability density functions of surface air temperatures in the North Atlantic/European region are affected by the multidecadal variability of the large-scale oceanic circulation. Thus, some useful decadal predictability may exist in the Atlantic/European sector

Apres Paris: nur Lippenbekenntnisse?

Auf der 21. UN-Klimakonferenz in Paris 2015 haben sich die Staaten darauf verständigt, die Erderwärmung auf „deutlich unter 2°C gegenüber der vorindustriellen Zeit“ zu begrenzen1). Man hofft, dass sich dadurch irreversible, d.h. unumkehrbare Prozesse vermeiden lassen, wie etwa das unwiderrufliche Abschmelzen des grönländischen Eisschilds oder der Westantarktis mit einem globalen Meeresspiegelanstieg von vielen Metern. Andere Beispiele für dramatische Auswirkungen des Klimawandels wären drastische Änderungen in den atmosphärischen und ozeanischen Zirkulationssystemen oder das Kippen von Ökosystemen auf Land oder in den Meeren. Oder auch die Zunahme und Intensivierung von Wetterextremen. Die Lage der Schwellenwerte, bei deren Überschreitung derartige Folgen eintreten würden, unterliegt jedoch einer großen Unsicherheit. Aus diesem Grund ist immer die geringste noch mögliche Erwärmung anzustreben

Northern Hemisphere interdecadal variability: A coupled air-sea mode

A coupled air–sea mode in the Northern Hemisphere with a period of about 35 years is described. The mode was derived from a multicentury integration with a coupled ocean–atmosphere general circulation model and involves interactions of the thermohaline circulation with the atmosphere in the North Atlantic and interactions between the ocean and the atmosphere in the North Pacific. The authors focus on the physics of the North Atlantic interdecadal variability. If, for instance, the North Atlantic thermohaline circulation is anomalously strong, the ocean is covered by positive sea surface temperature (SST) anomalies. The atmospheric response to these SST anomalies involves a strengthened North Atlantic Oscillation, which leads to anomalously weak evaporation and Ekman transport off Newfoundland and in the Greenland Sea, and the generation of negative sea surface salinity (SSS) anomalies. These SSS anomalies weaken the deep convection in the oceanic sinking regions and subsequently the strength of the thermohaline circulation. This leads to a reduced poleward heat transport and the formation of negative SST anomalies, which completes the phase reversal. The Atlantic and Pacific Oceans seem to be coupled via an atmospheric teleconnection pattern and the interdecadal Northern Hemispheric climate mode is interpreted as an inherently coupled air–sea mode. Furthermore, the origin of the Northern Hemispheric warming observed recently is investigated. The observed temperatures are compared to a characteristic warming pattern derived from a greenhouse warming simulation with the authors’ coupled general circulation model and also with the Northern Hemispheric temperature pattern associated with the 35-yr climate mode. It is shown that the recent Northern Hemispheric warming projects well onto the temperature pattern of the interdecadal mode under consideration

Warum ist es auf der Erde so schön warm?

Der Klimaforscher aus Kiel erzählt über seine Arbeit am Leibniz-Institut für Meereswissenschaften: Warum erlaubt das Klima nur auf der Erde Leben? Warum ist der Golfstrom eine gigantische Heizung für Westeuropa? Und welche Rolle spielen die Ozeane überhaupt im Klimasystem? Antworten auf diese Fragen gibt Professor Latif in seinem Vortrag