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Climate Change

House of Lords written question – answered on 24th April 2009.

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Photo of Lord Leach of Fairford Lord Leach of Fairford Conservative

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.

Photo of Lord Hunt of Kings Heath Lord Hunt of Kings Heath Minister of State (Sustainable Development, Climate Change Adaptation and Air Quality), Department for Environment, Food and Rural Affairs, Minister of State (Sustainable Development, Climate Change Adaptation and Air Quality), Department for Energy and Climate Change, Minister of State (Department of Energy and Climate Change), Minister of State (Department for Environment, Food and Rural Affairs) (Sustainable Development, Climate Change Adaptation and Air Quality) (also in the Department for Energy and Climate Change), Deputy Leader of the House of Lords

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.

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