transport (SST) airliners (a few hundred Boeing 2707s), which would fly in the lower stratosphere, could also deplete the ozone layer; however more recent analysis has disputed this as a large concern. He listed his main research interests as "Stratospheric and tropospheric chemistry, and their role in the biogeochemical cycles and climate". From 1980, he worked at the Department of Atmospheric Chemistry at the Max Planck Institute for Chemistry, in Mainz, Germany; the Scripps Institution of Oceanography at the University of California, San Diego; and at Seoul National University, South Korea. He was also a long-time adjunct professor at Georgia Institute of Technology and research professor at the department of meteorology at Stockholm University, Sweden. From 1997 to 2002 he was professor of aeronomy at the Department of Physics and Astronomy at Utrecht University. He co-signed a letter from over 70 Nobel laureate scientists to the Louisiana Legislature supporting the repeal of that U.S. state's creationism law, the Louisiana Science Education Act. In 2003 he was one of 22 Nobel laureates who signed the Humanist Manifesto. , Crutzen has an h-index of 151 according to Google Scholar and of 110 according to Scopus. Anthropocene One of Crutzen's research interests was the Anthropocene. In 2000, in IGBP Newsletter 41, Crutzen and Eugene F. Stoermer, to emphasize the central role of mankind in geology and ecology, proposed using the term anthropocene for the current geological epoch. In regard to its start, they said: To assign a more specific date to the onset of the "anthropocene" seems somewhat arbitrary, but we propose the latter part of the 18th century, although we are aware that alternative proposals can be made (some may even want to include the entire holocene). However, we choose this date because, during the past two centuries, the global effects of human activities have become clearly noticeable. This is the period when data retrieved from glacial ice cores show the beginning of a growth in the atmospheric concentrations of several "greenhouse gases", in particular CO2 and CH4. Such a starting date also coincides with James Watt's invention of the steam engine in 1784. Geoengineering (Climate intervention) Steve Connor, Science Editor of The Independent, wrote that Crutzen believes that political attempts to limit man-made greenhouse gases are so pitiful that a radical contingency plan is needed. In a polemical scientific essay that was published in the August 2006 issue of the journal