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Lindau Nobel Laureate Meetings - Global Warming by Hanna Kurlanda-Witek 2017 or 2018? The process of global warming begins with the release of greenhouse gases, such as methane, carbon dioxide, nitrous oxide, water vapour and fluorinated gases. Outgoing infrared radiation, or longwave radiation, is absorbed from the Earth’s surface by these gases as well as aerosols, hence the lower layers of the atmosphere become warmer, and less energy is emitted by the Earth’s surface. This is known as the greenhouse effect; without it, the Earth would be a very cold place, with a mean surface temperature about 33°C lower than it is now. But approximately since the beginning of the Industrial Age, the concentrations of greenhouse gases have reached unprecedented levels. The amount of carbon dioxide in the troposphere, or the lowest layer of the atmosphere, has risen from 280 ppm to about 400 ppm. methane levels have exceeded 1800 ppb, an increase from approximately 700 ppb in pre-Industrial times. The enormous amounts released into the atmosphere are both natural and linked to human activities. Here, Nobel Laureate Paul Crutzen describes the man-made and natural sources of methane emissions: Historical data demonstrate that the dynamics of global temperatures are correlated with the global carbon cycle. However, the association between rising greenhouse gas emissions and their effect on the climate, as well as to what extent these changes are brought about by anthropogenic activity, is still a matter of debate and controversy among scientists, let alone policymakers and the general public. To quote the topic cluster, “The Future” in the Lindau Mediatheque by David Siegel, “political, economic and scientific angles need to be considered”. There is evidence that the climate is becoming warmer. Many of us in Europe don’t need data from glacial ice cores – we can remember much colder winters and long periods of winter slowly turning into spring. In this lecture snippet, the biochemist and Nobel Laureate Hartmut Michel mentions his observations of first frosts in Germany, and explains a particular view on the evidence of global warming. A much stronger opinion is expressed by Mario Molina, who won the Nobel Prize in Chemistry in 1995, along with Paul Crutzen and F. Sherwood Rowland. It is likely that global warming will push the climate system past a tipping point, after which any preventive measures are futile – the damage will already be done. “You can’t play roulette with the planet”, explains Molina. 1