Isotope Curve (image) University of Copenhagen Caption The isotope curve shows that the emissions of the greenhouse gas methane had several peaks in the last 2,100 years. 1: During Roman times, where a lot of wood was burned for heating and for the processing of metals. 2: During the warm Middle Ages, where forests caught on fire. 3: In the "Little Ice Age", which was a very cold and dry period. 4: The methane concentration has increased dramatically since approx. the year 1800, when industrialization took off and triggered energy and food production, for example, rice fields. Credit NBI Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.