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It then started to rise, and its concentration is now nearly 50% higher than it was before the industrial revolution (Fig. 2). Other measurements that can fingerprint the source of this CO2 (e.g. isotopic data) confirm that the increase must be due to emissions from f****l f**l usage and human-induced changes vegetation and soils. Measurements from older ice cores (discussed below) confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years (Fig. 2). The fastest natural increase measured in older ice cores is around 15ppm (parts per million) over about 200 years. For comparison, atmospheric CO2 is now rising 15ppm every 6 years. Methane (CH4), another important greenhouse gas, also shows an unprecedented increase in concentration over the last two centuries. Its concentration is now much more than double its pre-industrial level. This is mainly due to emissions from agricultural sources and f****l f**l production, that comes on top of natural emissions from wetlands and other sources.



Natural c*****e c****e: glacial-interglacial cycles
By measuring the ratios of different water isotopes in polar ice cores, we can determine how temperature in Antarctica and Greenland has changed in the past. The oldest continuous ice core we have was drilled by the European Project for Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau (Fig. 3). It extends back 800,000 years and shows a succession of long, cold ‘glacial’ periods, interspersed roughly every 100,000 years by warm ‘interglacial’ periods (of which the last 11,000 years is the most recent). This succession of events is well-known from other records, and the coldest periods in Antarctica are the times when we had ice ages. Ice sheets extended over North America as far south as places like Chicago and New York, and over Britain to south of The Wash.