Jochem Marotzke, Directo, Climate Research, Max Planck Institute for Meteorology, Hamburg, Germany: Aren't you worried about thawing permafrost? No, quantitatively the contribution is relatively small. And as a general rule, it always says: Methane is a much more powerful greenhouse gas than CO₂, which is of course true: Overall, methane has a lower greenhouse gas effect than CO₂. Even if the permafrost thaws, it is uncertain how much of the methane really arrives in the atmosphere. Bacteria can convert methane to CO₂. I'm not worried about the methane. I am not concerned about any catastrophic climate tipping point from use of fossil fuels.