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To ask Her Majesty's Government at what point during the period of warming since the little ice age they consider that an anthropogenic warming signal greater than 0.25ºC per century was observed; and what the implications are for climate change policy.
The so-called little ice age generally refers to a relatively cool period between the 17th and mid-19th centuries in the north Atlantic region. There is no evidence that this was a global event. Global average temperature has risen by approximately 0.7 degrees centigrade since the late 19th century and the long-term upward trend appears to have begun in the early part of the 20th century. The IPCC's fourth assessment report concluded that human activity was responsible for most of this warming—in particular, that it is very likely (more than 90 per cent chance) that greenhouse gas emissions were responsible for most of the warming over the past 50 years, and likely (more than 66 per cent chance) that greenhouse gases caused some of the warming during the early 20th century. The average rate of warming over the 20th century was 0.74 degrees centigrade/century and nearly double that (1.28 degrees centigrade/century) in the second half. It is not possible to identify the exact date when an anthropogenic warming signal greater than 0.25 degrees centigrade per century (or 0.025 degrees centigrade per decade) was observed without performing complex analyses, but it is clear that the anthropogenic warming signal has been significantly greater than 0.25 degrees centigrade over the past century as a whole.