V. Petoukhov

• Potsdam Institute for Climate Impact Research

The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation patter...

The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern. We sho...

In May-June 2016 the Canadian Province of Alberta suffered one of the most devastating wildfires in its history. Here we show that in mid-April to early May 2016 the large-scale circulation in the mid- and high troposphere of the middle and sub-polar latitudes of the northern hemisphere featured a persistent high-amplitude planetary wave structure...

We present and validate a set of equations for representing the atmosphere's large-scale general circulation in an Earth system model of intermediate complexity (EMIC). These dynamical equations have been implemented in Aeolus 1.0, which is a statistical–dynamical atmosphere model (SDAM) and includes radiative transfer and cloud modules (Coumou et...

Several recent northern hemisphere summer extremes have been linked to persistent high-amplitude wave patterns (e.g. heat waves in Europe 2003, Russia 2010 and in the US 2011, Floods in Pakistan 2010 and Europe 2013). Recently quasi-resonant amplification (QRA) was proposed as a mechanism that, when certain dynamical conditions are fulfilled, can l...

Changes in atmospheric circulation can strongly alter the frequency and/or magnitude of high-impact extreme weather events. Here we address the link between circulation changes and the occurrence of long-lasting heat waves in the Northern Hemisphere summer. We show that boreal summer circulation has seen pronounced changes in circulation over the l...

Slow-moving planetary waves of high amplitudes are often associated with persistent surface weather conditions. This persistence can lead to extreme weather events with potentially serious implications for society and nature. Quasi-resonant amplification of planetary waves (QRA) has been proposed as a mechanism to generate high-amplitude hemisphere...

We present and validate a set of equations for representing the atmosphere's large-scale general circulation in an Earth system model of intermediate complexity (EMIC). These dynamical equations have been implemented in Aeolus, which is a Statistical Dynamical Atmosphere Model (SDAM) and includes radiative transfer and cloud modules (Coumou, 2011;...

Significance Weather extremes are becoming more frequent and severe in many regions of the world. The physical mechanisms have not been fully identified yet, but there is growing evidence that there are connections to planetary wave dynamics. Our study shows that, in boreal spring-to-autumn 2012 and 2013, a majority of the weather extremes in the N...

Paleoclimatic records show abrupt monsoon shifts at various different locations and historic periods (1⇓⇓⇓–5). An important question is whether such transitions are possible in the future (6). To this end, we carved out the physical mechanism for such transitions in a purposefully simple conceptual model (7). Recently, Boos and Storelvmo (8) claime...

In May 2014, the Balkans were hit by a Vb-type cyclone that brought disastrous flooding and severe damage to Bosnia and Herzegovina, Serbia, and Croatia. Vb cyclones migrate from the Mediterranean, where they absorb warm and moist air, to the north, often causing flooding in central/eastern Europe. Extreme rainfall events are increasing on a global...

Identifying regions important for spreading and mediating perturbations is crucial to assess the susceptibilities of spatio-temporal complex systems such as the Eartha € s climate to volcanic eruptions, extreme events or geoengineering. Here a data-driven approach is introduced based on a dimension reduction, causal reconstruction, and novel networ...

Lagged cross-correlation and regression analysis are commonly used to gain insights into interaction mechanisms between climatological processes, in particular to assess time delays and to quantify the strength of a mechanism. Exemplified on temperature anomalies in Europe and the tropical Pacific and Atlantic, the authors study lagged correlation...

Significance The recent decade has seen an exceptional number of boreal summer weather extremes, some causing massive damage to society. There is a strong scientific debate about the underlying causes of these events. We show that high-amplitude quasi-stationary Rossby waves, associated with resonance circulation regimes, lead to persistent surface...

Lagged cross-correlation and regression analysis are commonly used to gain insights into interaction mechanisms between climatological processes, in particular to assess time delays and to quantify the strength of a mechanism. Exemplified on temperature anomalies in Europe and the tropical Pacific and Atlantic, the authors study lagged correlation...

In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for Earth system models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single-column convective clouds. It distinguishes between ice and droplet clouds as well. Precipitation is calculate...

At the beginning of the Archean eon (ca. 3.8 billion yr ago), the Earth's climate state was significantly different from today due to the lower solar luminosity, smaller continental fraction, higher rotation rate and, presumably, significantly larger greenhouse gas concentrations. All these aspects play a role in solutions to the "faint young Sun p...

At the beginning of the Archean eon (ca. 3.8 billion years ago), the Earth's climate state was significantly different from today due to the lower solar luminosity, smaller continental fraction, higher rotation rate and, presumably, significantly larger greenhouse gas concentrations. All these aspects play a role in solutions to the "faint young Su...

Our recent article on quasiresonant amplification of planetary waves (1) has been addressed in a letter by Screen and Simmonds (2). They report, in particular, that they do not find statistically significant trends in the mean amplitudes of m = 6–8 waves in the 1979–2012 period. This observation does not contradict the statements made in our paper–...

In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for climate models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single column convective clouds. It distinguishes between ice and droplet clouds as well. Precipitation is calculated by...

During the Archean eon (3.8-2.5 billion years ago), the Sun was up to 25% less luminous than today, yet there is convincing evidence that the Earth's ocean surface was not completely frozen during this time period. As the Earth's rotation rate was higher and the continental fraction smaller than today, the climate system and, particularly, its resp...

In recent years, the Northern Hemisphere has suffered several devastating regional summer weather extremes, such as the European heat wave in 2003, the Russian heat wave and the Indus river flood in Pakistan in 2010, and the heat wave in the United States in 2011. Here, we propose a common mechanism for the generation of persistent longitudinal pla...

During the Archean (3.8-2.5 billion years ago), the Sun was up to 25% less luminous than today, yet there is strong evidence that the Earth's ocean surface was not completely frozen. The most obvious solutions to this ‘faint young Sun problem’ demand high concentrations of greenhouse gases such as carbon dioxide. Here we present the first comprehen...

Multivariate transfer entropy (TE) is a model-free approach to detect causalities in multivariate time series. It is able to distinguish direct from indirect causality and common drivers without assuming any underlying model. But despite these advantages it has mostly been applied in a bivariate setting as it is hard to estimate reliably in high di...

We present a new set of statistical-dynamical equations (SDEs) which can accurately reproduce the three-dimensional atmospheric fields of synoptic scale kinetic en-ergy and momentum flux. The set of equations is closed by finding proper parameterizations for the vertical macro-turbulent diffusion coefficient and ageostrophic terms. The equations ha...

Global and regional climate models, such as those used in IPCC assessments, are the best tools available for climate predictions. Such models typically account for large-scale land-atmosphere feedbacks. However, these models omit local vegetation-environment feedbacks that may be crucial for critical transitions in ecosystems at larger scales. In t...

Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and...

The recent overall Northern Hemisphere warming was accompanied by several severe northern continental winters, in particular extremely cold winter 2005/2006 in Europe and northern Asia. Here we show that these cold extremes might be favored by anomalous sea ice reduction in the Barents and Kara Seas in the Eastern Arctic. Atmospheric general circul...

Mineral dust particles provide the dominant contribution to the aerosol mass in the atmosphere while showing enormous variations in space and time. Dust deposition flux data range over more than four orders of magnitude. The largest values are reconstructed from Asian loess areas, followed by values from the Arabian Sea and the low latitudes in the...

The atmospheric burden of mineral dust is controlled by processes of dust emission, transport and deposition. Changes in vegetation cover from natural or anthropogenic climate change are a key factor for changes in dust emission. Increases in surface temperature and precipitation imply a decrease of the land area with no or little vegetation cover...

We use a coupled climate–carbon cycle model of intermediate complexity to investigate scenarios of stratospheric sulfur injections as a measure to compensate for CO2-induced global warming. The baseline scenario includes the burning of 5,000GtC of fossil fuels. A full compensation of CO2-induced warming requires a load of about 13MtS in the stratos...

In this paper the authors perform an extensive sensitivity analysis of the Indian summer monsoon rainfall to changes in parameters and boundary conditions which are influenced by human activities. For this study, the authors use a box model of the Indian monsoon which reproduces key features of the observed monsoon dynamics such as the annual cours...

In the Earth's history, periods of relatively stable climate have often been interrupted by sharp transitions to a contrasting state. One explanation for such events of abrupt change is that they happened when the earth system reached a critical tipping point. However, this remains hard to prove for events in the remote past, and it is even more di...

Based on the ERA40 data for 1976–2002 we calculated skewnesses and mixed third-order statistical moments (TOMs) for the synoptic variations [with (2.5–6) d timescales] of horizontal winds, temperature, vertical velocity and the specific humidity in Eulerian coordinates. All these variables show skewnesses which markedly deviate from zero, basically...

The Earth system model CLIMBER-2 is extended by a scheme for calculating the climatic response to anthropogenic sulphur dioxide emissions. The scheme calculates the direct radiative forcing, the first indirect cloud albedo effect, and the second indirect cloud lifetime effect induced by geographically resolved sulphate aerosol burden. The simulated...

Based on the ERA40 data for 1976–2002 we calculated skewnesses and mixed third-order statistical moments (TOMs) for the synoptic variations [with (2.5–6) d timescales] of horizontal winds, temperature, vertical velocity and the specific humidity in Eulerian coordinates. All these variables show skewnesses which markedly deviate from zero, basically...

An intercomparison of eight EMICs (Earth system Models of Intermediate Complexity) is carried out to investigate the variation and scatter in the results of simulating (1) the climate characteristics at the prescribed 280ppm atmosphere CO2 concentration, and (2) the equilibrium and transient responses to CO2 doubling in the atmosphere. The results...

The stability of the Indian summer monsoon is investigated by means of a box model of the tropical atmosphere. At the heart of this model is the moisture-advection feedback which allows for the existence of two stable regimes: besides the ``wet'' summer monsoon, a stable state exists which is characterized by low precipitation. The model is employe...

The sensitivity of the last glacial-inception (around 115kyrBP, 115,000years before present) to different feedback mechanisms has been analysed by using the Earth system model of intermediate complexity CLIMBER-2. CLIMBER-2 includes dynamic modules of the atmosphere, ocean, terrestrial biosphere and inland ice, the last of which was added recently...

We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at...

Large-scale instabilities of the Laurentide ice sheet (Heinrich events, HEs) are simulated with the 3-D polythermal ice-sheet model SICOPOLIS which is coupled bi-directional with the climate component of the Earth-system model CLIMBER-2. SICOPOLIS simulates the thickness, velocity, temperature and water-content for grounded ice sheets. In this vers...

A new conceptual dynamical model of ice sheet basal creep and sliding is proposed. By virtue of nonstationarity and high nonlinearity, the model displays multi-equilibria and reveals bifurcational features which depend on the type of the ice sheet bed. Based on modern estimates of thickening/thinning rates at different sites of the Greenland ice sh...

By using a climate system model of intermediate complexity, we have simulated long-term natural climate changes occurring over the last 9000 years. The paleo-simulations in which the model is driven by orbital forcing only, i.e., by changes in insolation caused by changes in the Earth's orbit, are compared with sensitivity simulations in which vari...

The stability of the climate-vegetation system in the northern high latitudesis analysed with three climate system models of different complexity: A comprehensive 3-dimensional model of the climate system, GENESIS-IBIS, and two Earth system models of intermediate complexity (EMICs), CLIMBER-2 andMoBidiC. The biogeophysical feedback in the latitudin...

The concept and theoretical background are presented of the hierarchy of Potsdam Statistical-Dynamical Atmospheric Models (POTSDAM). In this, the procedure of the derivation of the generalized statistical-dynamical equations (SDEs) is described at length which are the result of the spatial and temporal averaging of the primitive Reynolds-type hydro...

Heinrich events, related to large-scale surges of the Laurentide ice sheet, represent one of the most dramatic types of abrupt climate change occurring during the last glacial. Here, using a coupled atmosphere-ocean-biosphere-ice sheet model, we simulate quasi-periodic large-scale surges from the Laurentide ice sheet. The average time between simul...

Multiple proxy data reveal that the early to middle Holocene (ca. 8-6 kyr B.P.) was warmer than the preindustrial period in most regions of the Northern Hemisphere. This warming is presumably explained by the higher summer insolation in the Northern Hemisphere, owing to changes in the orbital parameters. Subsequent cooling in the late Holocene was...

We propose a new perspective on the hierarchy of climate models which goes beyond the "classical" climate modeling pyramid that is restricted mainly to atmospheric processes. Most notably, we introduce a new indicator, called "integration", which characterizes the number of interacting components of the climate system being explicitly described in...

At the early Holocene, about 9,000-8,000 years BP, the climate system was at the end of transition from glacial conditions to interglacial state. Multiple proxy data reveal that summer climate at the early to mid Holocene was warmer in the northern hemi- sphere, presumably due to changes in orbital forcing. At the same time, data from Vostok and Ta...

 A set of sensitivity experiments with the climate system model of intermediate complexity CLIMBER-2 was performed to compare its sensitivity to changes in different types of forcings and boundary conditions with the results of comprehensive models (GCMs). We investigated the climate system response to changes in freshwater flux into the Northern A...

A 2.5-dimensional climate system model of intermediate complexity CLIMBER-2 and its performance for present climate conditions are presented. The model consists of modules describing atmosphere, ocean, sea ice, land surface processes, terrestrial vegetation cover, and global carbon cycle. The modules interact through the fluxes of momentum, energy,...

We present a new reduced-form model for climate system analysis. This model, called CLIMBER-2 (for CLIMate and BiosphERe, level 2), fills the current gap between simple, highly parameterized climate models and computationally expensive coupled models of global atmospheric and oceanic circulation. We outline the basic assumptions implicit in CLIMBER...

In this study we determined characteristic temporal modes of atmospheric variability at the decadal and interdecadal timescales. This was done on the basis of 1000 year long integrations of a global coupled atmosphere-ocean climate model of moderate complexity including the troposphere, stratosphere, and mesosphere. The applied model resolves expli...

In order to estimate the effect of historical land cover change (deforestation) on climate, we perform a set of experiments with a climate system model of intermediate complexity – CLIMBER-2. We focus on the biophysical effect of the land cover change on climate and do not explicitly account for the biogeochemical effect. A dynamic scenario of defo...

A conceptual model has been developed for the analysis of atmosphere-vegetation interaction in subtropical deserts. The model can exhibit multiple stable states in the system: a ``desert'' equilibrium with low precipitation and absent vegetation and a ``green'' equilibrium with moderate precipitation and permanent vegetation cover. The conceptual m...

Simulations with a synchronously coupled atmosphere–ocean–vegetation model show that changes in vegetation cover during the mid-Holocene, some 6000 years ago, modify and amplify the climate system response to an enhanced seasonal cycle of solar insolation in the Northern Hemisphere both directly (primarily through the changes in surface albedo) and...

By coupling an atmospheric general circulation model asynchronously with an equilibrium vegetation model, manifold equilibriu solutions of the atmosphere–biosphere system have been explored. It is found that under present–day conditions of the Earth' orbital parameters and sea–surface temperatures, two stable equilibria of vegetation patterns are p...

A global coupled ocean-atmosphere model of intermediate complexity is used to simulate the equilibrium climate of both today and the Last Glacial Maximum, around 21,000 years ago. The model successfully predicts the atmospheric and oceanic circulations, temperature distribution, hydrological cycle and sea-ice covet of both periods without using 'fl...

This paper describes a methodology that combines the outputs of (1) the Integrated Model to Assess the Greenhouse Effect (IMAGE Version 1.0) of the Netherlands National Institute of Public Health and Environmental Protection (RIVM) (given a greenhouse gas emission policy, this model can estimate the effects such as global mean surface air temperatu...