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Anpassungen sind zwingend, Tagblatt, März 2014

Winterkälte und Meereis, NZZ, Januar 2014

Interview Horizonte, Dezember 2013

Extreme Wetterereignisse ändern sich, Tagesschau, SRF, November 2013

Langfristig ist der Einfluss der Menschen dominant, SRF 4 News, November 2013

Und die Erde erwärmt sich doch, Sonntagszeitung, November 2013

Das Wetter wird extrem, 20 Minuten, November 2013

Klimaveränderung ist eindeutig, Tagblatt, November 2013

How to Slice a Global Carbon Pie?, New York Times, October 2013

Können wir die Welt überhaupt noch retten?, Blick, Oktober 2013

Das Ausmass der Erwärmung bestimmen wir!, EE News, Oktober 2013

Heiter bis wolkig: Winzige Tropfen bestimmen den Klimawandel, Rhein-Neckar Zeitung, November 2013

Das CO2-Budget ist schon fast weg, Basler Zeitung, Oktober 2013

Nicht nur für die Inseln wird es brenzlig, Neue Luzerner Zeitung, September 2013

Klimawandel: Zwei Drittel des CO2-Budgets sind schon aufgebraucht, Tagesanzeiger, September 2013 Teil 1, Teil2, Teil 3

Klima-Report: Wissenschaft und Politik sind sich einig; SRF Autorenbeitrag, September 2013

Warum macht der Klimawandel Pause? (Teil 1), FAZ, September 2013

Warum macht der Klimawandel Pause? (Teil 2), FAZ, September 2013

Der Klimawandel scheint eine Pause einzulegen, SF Tagesschau, August 2013

Leaked IPCC report doesn't let us off the hook, New Scientist, July 2013

Auch kleine Meereswirbel ändern das Wetter, 20 Minuten, Juli 2013

Erderwärmung macht Pause, Interview Tagblatt, Juni 2013

Klimawandel langsamer – aber keine Entwarnung, 3sat nano, Mai 2013

Klimaerwärmung weniger stark als befürchtet, Radio SRF, Echo der Zeit, Mai 2013

Warum ist es so saukalt, Herr Professor?, Sonntagsblick, Mai 2013

Die Klimapause, Tagesanzeiger, Mai 2013

Wir wissen genug, um zu entscheiden, Wochenspiegel, Mai 2013

Pourquoi le réchauffement s’est ralenti, Le Temps, April 2013

A sensitive matter, Economist, March 2013

Kühlende Vulkane, Sonntagszeitung, März 2013

Wissenschaft im Gespräch, SRF2, März 2013

SF TV 10 vor 10 zu Doha, Dezember 2012

Interview Swiss Radio International December 2012

DRS3 zu Doha, November 2012

Interview Sonntagszeitung, November 2012

Neuer OcCC Bericht, SF Tagesschau, November 2012

An den Grenzen der Klimamodelle, ETH Life, November 2011

Vier Grad zu heiss, Tagblatt, November 2012

Der Spielraum für Klimaschutz schrumpft, Tagesanzeiger, November 2012

Auf Kosten zukünftiger Generationen, Die Politik, Oktober 2012

Hagelsommer 2012, SF TV Einstein, September 2012

Der ideale Preis fürs Klima, Sonntagszeitung, September 2012

Unsicherheit als Ausrede, SNF Horizonte, September 2012

Aussergewöhnliche Eisschmelze in Grönland, Radio DRS, Juli 2012

Brutus lässt die Rechenkerne glühen, NZZ, Juni 2012

Von nichts kommt nichts, Editorial Physik in unserer Zeit, Mai 2012

Wir müssen den Klimaschutz entschiedener angehen, Interview DRS4, Dezember 2011

Der Klimaschutz muss noch deutlich schneller voran kommen, Interview Nachhaltigleben, Dezember 2011

Aus der Sicht des Klimas ist Durban eine Nullrunde, Tagesanzeiger, Dezember 2011

WDR Radio Interview, Dezember 2011

Das Klima verdüstert sich, Autorenbeitrag NZZ am Sonntag, November 2011

Der Wert der Eisbären, Tagblatt Interview, November 2011

Nur mit Verzicht funktioniert das nicht, Sonntagszeitung, November 2011

Die immer gleichen Verlierer, Sonntagszeitung, November 2011

Wie weiter mit dem Klimaschutz, DRS2 Kontext, November 2011

SF Tagesschau über CH2011

Teletop über CH2011 (ab 5min 30sec)

World Radio International über CH2011, September 2011

DRS Echo der Zeit über CH2011

Die Natur würde verrückt spielen, Tagesanzeiger, Juli 2011
Gibt es immer mehr Wetterkatastrophen?, Blick online, Februar 2011

Schöne Aussichten dank Klimawandel, Blick am Abend, Januar 2011

Menschen 2011 (Seite 3), Sonntagszeitung, Januar 2011

Click here for full list...

Selected recent publications

Robustness and uncertainties in the new CMIP5 climate model projections, Nature Climate Change 2012

Communication of the role of natural variability in future North American climate, Nature Climate Change Perspective 2012

Robust joint projections for humidity and temperature extremes, Nature Climate Change 2012

Anthropogenic and natural warming inferred from changes in Earth’s energy balance, Nature Geoscience 2011

Long-term climate implications of twenty-first century options for carbon dioxide emission mitigation, Nature Climate Change 2011

Climate model genealogy, GRL 2011

The end of model democracy?, Climatic Change 2010

Greenhouse-gas emission targets for limiting global warming to 2°C, Nature 2009

Irreversible climate change due to carbon dioxide emissions, PNAS 2009

Review climate sensitivity, Nature Geoscience 2008

Should we believe model predictions of future climate change?, Phil Trans Roy Soc 2008

Click here for full list...


Quick links

Main page Reto Knutti

Publications

Research

Presentation/Media


I use several climate models of different complexity, from intermediate complexity to general circulation models for my work. Below is a short summary on a few topics.

Process studies on the ocean thermohaline circulation

For my studies on the large-scale ocean thermohaline circulation, I use the Bern 2.5D Climate Model. This model is designed to study the role of the thermohaline circulation in the Earth climate system of the past, present and future. My early work focussed on the stability and dynamics of the thermohaline circulation on timescales of more than several decades and on spatial scales of more than a thousand kilometers. The simple parameterization of processes results in a computationally efficient climate model suitable for long-term integrations (up to millions of years) and large numbers of simulations not feasible with more complex models. This allows us to focus in detail on the mechanisms and processes of natural climate variability and on the potential anthropogenic climate change.

Probabilistic projections with very large model ensembles

The extreme efficiency of the zonally averaged climate model also allows to calculate ensemble simulations of several thousand members. This approach has recently been used to demonstrate a strategy of how probabilistic forecasts of climate change over the next century can be obtained. The idea is to run a model many times with different parameter combinations and then used observations to constrain the ensemble, i.e. give those model versions more weight that agree well with observations. Technically, these are Bayesian methods, and the result of this procedure is a probability density function of future warming given the observations of the past century.

Uncertainties in global temperature for SRES scenarios B1 and A2
Uncertainties in global temperature for SRES scenarios B1 and A2

Further details can be found in Knutti et al., Nature 2002 (PDF file: 0.2 MB), or in the related News&Views.

Regional probabilistic projections from comprehensive models

Although global mean temperature is a good overall indicator of the expected changes, people are more interested in regional climate projections, since those determine local impacts. We used output from twenty different coupled atmosphere ocean general circulation models and a Bayesian method to obtain regional probabilistic projections of future warming. Instead of calculating just a model mean, this allows for instance to quantify the warming that is likely to occur, i.e. the warming that will be exceeded with at 80% probability. Such models also allow to differentiate between summer and winter changes, and to quantify trends variability and extreme events.

'Likely' warming in 2100 for SRES scenario A1B
'Likely' warming in 2100 for SRES scenario A1B
SRES A1B 2100 multi model mean surface warming
SRES A1B 2100 multi model mean surface warming (°C)


Further details can be found in Furrer et al. GRL 2007 (PDF file).

Paleoclimate modeling

Using the Ecbilt-CLIO climate model we also studied how the ocean connects the polar regions of Greenland and Antarctica during the abrupt climate events in the last ice age, about 50,000 years ago. For the first time, we proposed an improved 'bipolar seesaw' concept, the so-called 'thermal freshwater seesaw' that explains most of the timing and amplitude in the Greenland and Antarctic temperature proxies as well as sea level. The model also captures surprisingly many features of the spatial patterns of temperature and precipitation changes as reconstructed from proxy data. The figure below shows the surface temperature difference simulated by the model when the Atlantic thermohaline circulation switches from a collapsed state to an active state with deepwater formation in the North Atlantic. The associated increased northward heat transport of the ocean causes the North Atlantic to warm by 15 degrees C or more within several decades and the Southern Ocean to cool (the seesaw).

Temperature change for an abrupt warm event in the last glacial period
Temperature change for an abrupt warm event in the last glacial period

Further details can be found in Knutti et al., Nature 2004 (PDF file: 0.8 MB), or in the related News&Views

For more detailed information, please see the Publications page. 

 

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