Claudia Timmreck

Aerosol size confines climate response to volcanic super-eruptions

Extremely large volcanic eruptions have been linked to global climate change, biotic turnover, and, for the Younger Toba Tuff (YTT) eruption 74,000 years ago, near-extinction of modern humans. One of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles. A huge atmospheric concentration of sulfate causes higher collision rates, larger particle sizes, and rapid fall out, which in turn greatly affects radiative feedbacks. We address this key process by incorporating the effects of aerosol microphysical processes into an Earth System Model. The temperature response is shorter (9–10 years) and three times weaker (−3.5 K at maximum globally) than estimated before, although cooling could still have reached −12 K in some midlatitude continental regions after one year. The smaller response, plus its geographic patchiness, suggests that most biota may have escaped threshold extinction pressures from the eruption.

Emissions from volcanoes

Around 380 volcanoes were active during the last century, with around 50 volcanoes active per year (Andres and Kasgnoc, 1998). Volcanic activity is not randomly distributed over the Earth, but is linked to the active zones of plate tectonics, as shown in figure 1. More than 2/3 of the world’s volcanoes are located in the northern hemisphere, and in tropical regions. The emission of volcanic gases depends on the thermodynamic conditions (pressure, temperature) and on the magma type (i.e., its chemical composition, which in turn depends on the tectonic environment).

Stratospheric Aerosol--Observations, Processes, and Impact on Climate

Interest in stratospheric aerosol and its role in climate have increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any nonvolcanically driven change, making them difficult to understand. While the role of carbonyl sulfide as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of nonsulfate matter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes.

Tambora 1815 as a test case for high impact volcanic eruptions: Earth system effects

The eruption of Tambora (Indonesia) in April 1815 had substantial effects on global climate and led to the ‘Year Without a Summer’ of 1816 in Europe and North America. Although a tragic event—tens of thousands of people lost their lives—the eruption also was an ‘experiment of nature’ from which science has learned until today. The aim of this study is to summarize our current understanding of the Tambora eruption and its effects on climate as expressed in early instrumental observations, climate proxies and geological evidence, climate reconstructions, and model simulations. Progress has been made with respect to our understanding of the eruption process and estimated amount of SO2 injected into the atmosphere, although large uncertainties still exist with respect to altitude and hemispheric distribution of Tambora aerosols. With respect to climate effects, the global and Northern Hemispheric cooling are well constrained by proxies whereas there is no strong signal in Southern Hemisphere proxies. Newly recovered early instrumental information for Western Europe and parts of North America, regions with particularly strong climate effects, allow Tamboras effect on the weather systems to be addressed. Climate models respond to prescribed Tambora‐like forcing with a strengthening of the wintertime stratospheric polar vortex, global cooling and a slowdown of the water cycle, weakening of the summer monsoon circulations, a strengthening of the Atlantic Meridional Overturning Circulation, and a decrease of atmospheric CO2. Combining observations, climate proxies, and model simulations for the case of Tambora, a better understanding of climate processes has emerged. WIREs Clim Change 2016, 7:569–589. doi: 10.1002/wcc.407 This article is categorized under: 1 Paleoclimates and Current Trends > Paleoclimate

Sensitivity of a coupled climate‐carbon cycle model to large volcanic eruptions during the last millennium

The sensitivity of the climate–biogeochemistry system to volcanic eruptions is investigated using the comprehensive Earth System Model developed at the Max Planck Institute for Meteorology. The model includes an interactive carbon cycle with modules for terrestrial biosphere as well as ocean biogeochemistry. The volcanic forcing is based on a recent reconstruction for the last 1200 yr. An ensemble of five simulations is performed and the averaged response of the system is analysed in particular for the largest eruption of the last millennium in the year 1258. After this eruption, the global annual mean temperature drops by 1 K and recovers slowly during 10 yr. Atmospheric CO2 concentration declines during 4 yr after the eruption by ca. 2 ppmv to its minimum value and then starts to increase towards the pre-eruption level. This CO2 decrease is explained mainly by reduced heterotrophic respiration on land in response to the surface cooling, which leads to increased carbon storage in soils, mostly in tropical and subtropical regions. The ocean acts as a weak carbon sink, which is primarily due to temperature-induced solubility. This sink saturates 2 yr after the eruption, earlier than the land uptake.

A one and half year interactive MA/ECHAM4 simulation of Mount Pinatubo Aerosol

The Mount Pinatubo volcanic eruption in June 1991 had significant impact on stratospheric and tropospheric climate and circulation. Enhanced radiative heating caused by the aerosol absorption of solar and terrestrial radiation changed stratospheric temperature and circulation. Using the stratospheric mesospheric version of the Hamburg climate model MA/ECHAM4, we performed an interactive Pinatubo simulation with prognostic stratospheric aerosol. Interactive and noninteractive model results for the years 1991 and 1992 are compared with satellite data and in situ measurements. The on-line calculated heating rates are in good agreement with radiation transfer models indicating maximum heating rates of about 0.3 K/d in October 1991. The dynamic feedback in the MA/ECHAM4 simulation is similar to observations. The model is able to reproduce the strengthening of the polar vortex in winter 1991/1992 and a minor warming in January. The importance of an interactive treatment of the volcanic cloud for the aerosol transport is evidenced by the analysis of effects such as aerosol lifting and meridional transport. In general, the model results agree well with observations from the northern midlatitudes, especially in the first months after the eruption. The MA/ECHAM4 model is successful in reproducing the formation of two distinct maxima in the optical depth but is unable to simulate the persistence of the tropical aerosol reservoir from the end of 1991. Better agreement may be achieved if the influence of the quasi-biennial oscillation and ozone changes is also taken into account.

Heterogeneous nucleation as a potential sulphate‐coating mechanism of atmospheric mineral dust particles and implications of coated dust on new particle formation

[1] The plausibility of heterogeneous conucleation of water, sulphuric acid, and ammonia as a pathway leading to soluble coating of atmospheric mineral dust is investigated. In addition, the effect of such sulphate-coated dust on the formation and growth of atmospheric aerosol particles is addressed. The simulated new particle formation mechanism is ternary nucleation of water, sulphuric acid, and ammonia vapors, while in the condensational growth process the effect of condensable organic vapor is also studied. The results indicate that soluble coating of dust by heterogeneous nucleation can occur at atmospheric sulphuric acid concentrations. In addition, the simulations show that homogeneous ternary nucleation and subsequent growth are decoupled. Although observed (or even higher) dust concentrations are unable to inhibit new particle formation, coated dust particles acting as condensation and coagulation sinks can prevent the growth of newly formed particles to detectable sizes. This is particularly true in desert areas, where organic vapor concentrations are low. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 3210 Mathematical Geophysics: Modeling; KEYWORDS: aerosol, mineral dust, soluble coating, heterogeneous nucleation, particle formation and growth, condensation sink

Three‐dimensional simulation of stratospheric background aerosol: First results of a multiannual general circulation model simulation

A sulfuric acid aerosol model has been implemented in the global general circulation model ECHAM4. This model treats the formation, the development, and the transport of stratospheric sulfuric acid aerosol. The aerosol size distribution and the sulfuric acid mass fraction are calculated as a function of the H2SO4/H2O concentration, temperature, and air pressure in a size range between 0.001 μ and 2.58 μ. Binary homogeneous nucleation of H2SO4/H2O, condensation and evaporation of H2SO4 and H2O, Brownian coagulation and gravitational sedimentation are included. The microphysical model for stratospheric sulfate aerosol and a stratospheric sulfur chemistry are combined with a representation of the tropospheric sulfur chemistry. This tropospheric scheme accounts for the natural and anthropogenic emissions, chemistry, and dry and wet deposition of DMS, SO2, and SO42−. Globally and seasonally different SO2− and SO42− sources for stratospheric aerosol can therefore be taken into account. Results of a multiannual simulation show that the simulated SO2 and H2SO4 concentrations are generally in good agreement with available observations. The formation of new particles through homogeneous nucleation takes place in the tropical lower stratosphere and upper troposphere and in polar spring. The aerosol surface area density and the aerosol mass concentration reproduce lower stratospheric background conditions quite well. Effective radius and aerosol mixing ratio agree also with satellite and in situ measurements at Northern Hemisphere midlatitudes.

Using a large ensemble of simulations to assess the Northern Hemisphere stratospheric dynamical response to tropical volcanic eruptions and its uncertainty

The observed strengthening of the Northern Hemisphere (NH) polar vortex after tropical volcanic eruptions appears to be underestimated by coupled climate models. However, there is only a limited number of observed eruptions, which makes the attribution of volcanic signals difficult, because the polar vortex is also influenced by other external forcing factors as well as internal variability. We show with a 100-member ensemble of historical (1850-2005) simulations with the MPI-ESM-LR that an ensemble larger than what is provided by the Coupled Model Intercomparison Project Phase 5 (CMIP5) models is needed to detect a statistically significant NH polar vortex strengthening. The most robust signal can be found when only the two strongest eruptions (Krakatau and Pinatubo) are considered in contrast to including smaller eruptions to increase the sample size. For these two strongest eruptions, also the mean of 15 CMIP5 models shows a statistically significant strengthening of the NH polar vortex.

MiKlip - a National Research Project on Decadal Climate Prediction

AbstractMittelfristige Klimaprognose (MiKlip), an 8-yr German national research project on decadal climate prediction, is organized around a global prediction system comprising the Max Planck Institute Earth System Model (MPI-ESM) together with an initialization procedure and a model evaluation system. This paper summarizes the lessons learned from MiKlip so far; some are purely scientific, others concern strategies and structures of research that target future operational use.Three prediction system generations have been constructed, characterized by alternative initialization strategies; the later generations show a marked improvement in hindcast skill for surface temperature. Hindcast skill is also identified for multiyear-mean European summer surface temperatures, extratropical cyclone tracks, the quasi-biennial oscillation, and ocean carbon uptake, among others. Regionalization maintains or slightly enhances the skill in European surface temperature inherited from the global model and also displays h...