See all climate myths in our special feature.
Some climate sceptics argue that the warming we are now experiencing is simply due to the planet recovering from the Little Ice Age, a period of regionally cold conditions between roughly AD 1350 and 1850. But the key question is why it was colder during the Little Ice Age. And why didn鈥檛 the climate remain that way, or even get colder still?
The Earth does not have some natural temperature to which it always returns. If it cools, then it must be receiving less heat from the Sun or radiating more into space, or both. If it warms, it must be receiving more heat or retaining more heat.
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The term 鈥淟ittle Ice Age鈥� is somewhat questionable, because there was no single, well-defined period of prolonged cold around the entire planet. After 1600, there are records of average winter temperatures in Europe and North America that were as much as 2掳C lower than present (although the in England since 1659 was in 1963).
Comparisons of temperature indicators such as tree-ring records from around the northern hemisphere suggest there were between 1580 and 1850.
Yet while there is some evidence of cold intervals in parts of the southern hemisphere during this time, they with those in the northern hemisphere. Such findings suggest the Little Ice Age may have been more of a regional phenomenon than a global one.
Heat transport
Solar radiation was probably lower at times during this period, especially during a dip in solar activity called the Maunder minimum around 1700, but models and temperature reconstructions suggest this would have reduced average global temperatures .
The larger falls in temperature in Europe and North American may have been due to changes in atmospheric circulation over the North Atlantic, or in the Gulf Stream, or both, reducing heat transport from the tropics (see Climate change sceptics lose vital argument).
The warming after the so-called Little Ice Age may reflect both an increase in solar activity and a redistribution of heat around the planet. In particular, the increase in global temperature in the first half of the 20th century may have been largely due to an increase in solar activity. The continued warming in recent decades, however, cannot be explained by increases in solar radiation alone (see Climate myths: Global warming is down to the Sun, not humans).
