Showing papers by "Paul J. Crutzen published in 2007"

The Anthropocene: are humans now overwhelming the great forces of Nature?

Abstract: We explore the development of the Anthropocene, the current epoch in which humans and our societies have become a global geophysical force. The Anthropocene began around 1800 with the onset of industrialization, the central feature of which was the enormous expansion in the use of fossil fuels. We use atmospheric carbon dioxide concentration as a single, simple indicator to track the progression of the Anthropocene. From a preindustrial value of 270-275 ppm, atmospheric carbon dioxide had risen to about 310 ppm by 1950. Since then the human enterprise has experienced a remarkable explosion, the Great Acceleration, with significant consequences for Earth System functioning. Atmospheric CO2 concentration has risen from 310 to 380 ppm since 1950, with about half of the total rise since the preindustrial era occurring in just the last 30 years. The Great Acceleration is reaching criticality. Whatever unfolds, the next few decades will surely be a tipping point in the evolution of the Anthropocene.

Civil Aircraft for the regular investigation of the atmosphere based on an instrumented container: The new CARIBIC system

Abstract: An airfreight container with automated instruments for measurement of atmospheric gases and trace compounds was operated on a monthly basis onboard a Boeing 767-300 ER of LTU International Airways during long-distance flights from 1997 to 2002 (CARIBIC, Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, http://www.caribic-atmospheric.com). Subsequently a more advanced system has been developed, using a larger capacity container with additional equipment and an improved inlet system. CARIBIC phase #2 was implemented on a new long-range aircraft type Airbus A340-600 of the Lufthansa German Airlines (Star Alliance) in December 2004, creating a powerful flying observatory. The instrument package comprises detectors for the measurement of O3, total and gaseous H2O, NO and NOy, CO, CO2, O2, Hg, and number concentrations of sub-micrometer particles (>4 nm, >12 nm, and >18 nm diameter). Furthermore, an optical particle counter (OPC) and a proton transfer mass spectrometer (PTR-MS) are incorporated. Aerosol samples are collected for analysis of elemental composition and particle morphology after flight. Air samples are taken in glass containers for laboratory analyses of hydrocarbons, halocarbons and greenhouse gases (including isotopic composition of CO2) in several laboratories. Absorption tubes collect oxygenated volatile organic compounds. Three differential optical absorption spectrometers (DOAS) with their telescopes mounted in the inlet system measure atmospheric trace gases such as BrO, HONO, and NO2. A video camera mounted in the inlet provides information about clouds along the flight track. The flying observatory, its equipment and examples of measurement results are reported.

Stratospheric dryness: model simulations and satellite observations

Abstract: The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of comprehensive models which are able to reproduce the observations. Here we examine results from the coupled lower-middle atmosphere chemistry general circulation model ECHAM5/MESSy1 together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent the seasonal and inter-annual variability of water vapor. The model reproduces the very low water vapor mixing ratios (below 2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured. Our results confirm that the entry of tropospheric air into the tropical stratosphere is forced by large-scale wave dynamics, whereas radiative cooling regionally decelerates upwelling and can even cause downwelling. Thin cirrus forms in the cold air above cumulonimbus clouds, and the associated sedimentation of ice particles between 100 and 200 hPa reduces water mass fluxes by nearly two orders of magnitude compared to air mass fluxes. Transport into the stratosphere is supported by regional net radiative heating, to a large extent in the outer tropics. During summer very deep monsoon convection over Southeast Asia, centered over Tibet, moistens the stratosphere.

Methane emissions from boreal and tropical forest ecosystems derived from in-situ measurements

Abstract: . Methane is a climatologically important greenhouse gas, which plays a key role in regulating water vapour in the stratosphere and hydroxyl radicals in the troposphere. Recent findings that vegetation emits methane have stimulated efforts to ascertain the impact of this source on the global budget. In this work, we present the results of high frequency (ca. 1 min−1) methane measurements conducted in the boreal forests of Finland and the tropical forests of Suriname, in April–May, 2005 and October 2005 respectively. The measurements were performed using a gas chromatograph – flame ionization detector (GC-FID). The average of the median mixing ratios during a typical diel cycle were 1.83 μmol mol−1 and 1.74 μmol mol−1 for the boreal forest ecosystem and tropical forest ecosystem respectively, with remarkable similarity in the time series of both the boreal and tropical diel profiles. Night time methane emission flux of the boreal forest ecosystem, calculated from the increase of methane during the night and measured nocturnal boundary layer heights yields a flux of (3.62±0.87)×1011 molecules cm−2 s−1(or 45.5±11 Tg CH4 yr−1 for global boreal forest area). This is a source contribution of circa 8% of the global methane budget. These results highlight the importance of the boreal and tropical forest ecosystems for the global budget of methane. The results are also discussed in the context of recent work reporting high methane mixing ratios over tropical forests using space borne near infra-red spectroscopy measurements.

Analysis of the CEPEX ozone data using a 3D chemistry‐meteorology model

Abstract: The ozone (O3) data collected during the Central Equatorial Pacific Experiment (CEPEX) are analysed with the aid of the 3D global photochemistry model MATCH-MPIC (Model of Atmospheric Transport and Chemistry-Max-Planck-Institute for Chemistry version). This study focuses on using MATCH-MPIC to address three specific questions: (1) are the individual CEPEX O3 soundings, in particular the extremely low O3 levels occasionally observed in the upper troposphere (UT), reproducible by a state-of-the-art global photochemical model driven with analysed meteorological data from the same time period as the measurements (March 1993): (2) are the CEPEX O3 data likely to be representative of the mean state of the regional atmosphere, or do they instead indicate the degree of variability in this region of the atmosphere; and (3) what causes the UT O3 minima? It is found that MATCH-MPIC is not able to reproduce the soundings obtained during CEPEX on an individual basis; however, the model does reproduce some of the key features present in the observations, such as UT minima and mid-tropospheric maxima similar to those observed during CEPEX. the UT O3 minima computed by the model are mainly due to convective pumping of low-O3 marine boundary-layer air, as is demonstrated by comparison with the results of a run in which convective transport of O3 is suppressed. the UT O3 minima simulated by MATCH-MPIC (with O3 between 5 and 10 nmol mol-1) are less intense than those observed (with O3 < 5 nmol mol-1), even at relatively high model spatial and temporal resolution, and with a convection scheme that would be expected to readily produce UT O3 minima via intense pumping of low-O3 marine boundary-layer air directly into the UT convective outflow regions. This may indicate that additional photochemical loss processes are involved, either in situ in the UT or, in particular, near the surface in the convective inflow regions. where the model tends to overestimate the observed O3 levels. In addition, although a significant temporal variability for O3 in this region is computed, it is still less than indicated by the observations in the UT. This high degree of variability implies that individual O3 soundings will often differ considerably from the mean over a longer period. For instance, 20-50% less O3 in the UT during the CEPEX period is computed with MATCH-MPIC than the average for March. Thus, the CEPEX expedition was perhaps fortunate in encountering extreme conditions which produced extensive UT O3 minima. which have helped to demonstrate one end of the large degree of variability of O3 in the tropical troposphere.

Frequent Ozone Depletion Resulting from Impacts of Asteroids and Comets

Abstract: The fossil record reveals that the evolution of life on Earth has been punctuated by a number of catastrophic events, of which one of the most devastating occurred at the end of the Cretaceous, approximately 66 million years ago. The postulate introduced in 1980 by Alvarez et al. (1980) that the collision of an approximately 10 km diameter asteroid with the Earth caused the extinction of the dinosaurs along with more than half of all plant and animal species has resulted in a greatly expanded research efforts in the area of catastrophic events (Alvarez et al. 1980).

The CARIBIC aircraft system for detailed, long-term, global-scale measurement of trace gases and aerosol in a changing atmosphere

Abstract: Contributed by Carl Brenninkmeijer (carlb@mpchmainz.mpg.de), Franz Slemr (slemr@mpch-mainz. mpg.de), Tanja Schuck (schuck@mpch-mainz.mpg.de), Dieter Scharffe (scharffe@mpch-mainz.mpg.de), Claus Koeppel, (koeppel@mpch-mainz.mpg.de), Martin Pupek (pupek@mpch-mainz.mpg.de), Patrick Jockel (Joeckel@mpch-mainz.mpg.de), Jos Lelieveld (lelieveld@mpch-mainz.mpg.de) and Paul Crutzen (crutzen@mpch-mainz.mpg. de), Max Planck Institute for Chemistry, Mainz, Germany, Tae Siek Rhee (rhee@ kopri.re.kr), Korea Polar Institute, Incheon, Korea, Markus Hermann (Hermann@tropos.de), Andreas Weigelt (andreas.weigelt@tropos.de), Manuela Reichelt (reichelt@chemie.uni-leipzig.de) and Jost Heintzenberg (jost@tropos.de), Leibniz Institute for Tropospheric Research, Leipzig, Germany, Andreas Zahn (zahn@imk.fzk.de), Detlev Sprung (sprung@ imk.fzk.de) and Herbert Fischer (Fischer@imk.fzk. de), Institute for Meteorology and Climate Research, Karslruhe, Germany, Helmut Ziereis (helmut.ziereis@ dlr.de), Hans Schlager (hans.schlager@dlr.de) and Ulrich Schumann (ulrich. schumann@dlr.de), Institute for Atmospheric Physics, DLR, Oberpfaffenhofen, Germany, Barbara Dix (bdix@iup.uni-heidelberg. de), Udo Friess (udo.friess@ iup.uni-heidelberg.de) and Ulrich Platt (Platt@iup.uniheidelberg.de), University of Heidelberg, Heidelberg, Germany, Ralf Ebinghaus (ralf.ebinghaus@gkss.de), GKSS, Geesthacht, Germany, Bengt Martinsson (bengt. martinsson@nuclear.lu.se) and Hung N. Nguyen (hung. ng uye n _ ngo c @ pi xe . l t h . se), Department of Nuclear Physics, University of Lund, Lund, Sweden, David Oram (d.e.oram@uea.ac.uk), Debbie O’Sullivan (debbie. osullivan@metoffice.gov.uk) and Stuart Penkett (M.Penkett@uea.ac.uk), University of East Anglia, Norwich, England, Peter van Velthoven (velthove@ knmi.nl) KNMI, de Bilt, the Netherlands, Thomas Rockmann (T.Roeckmann@phys.uu.nl) and Gerben Pieterse (G.Pieterse@phys.uu.nl), University of Utrecht, the Netherlands, Sergey Assonov (sergey.assonov@ ec.europa.eu), IRMM, Geel, Belgium, Michel Ramonet (michel.ramonet@cea.fr), Irene Xueref-Remy (irene. xueref@cea.fr) and Philippe Ciais (ciais@cea.fr), LSCE/ CEA/CNRS, Paris, France, Stefan Reimann (Stefan. Reimann@empa.ch) and Martin Vollmer (Martin. Vollmer@empa.ch), EMPA, Dubendorf, Switzerland, Markus Leuenberger (mleu@climate.unibe. ch) and Francesco Luca Valentino ( F r a n c e s c o L u c a .Va l e n t i n o @ insightful.com), University of Bern, Bern, Switzerland.