The last millennium is presented by relatively numerous proxy data, derived from trees, ice cores, and corals better than previous ones.
There is a lot of regional evidence, that, in the ninth to eleventh centuries, climate was warmer than today, the 'Medieval climatic optimum'. Amount of ice in the North Atlantics diminished. Glaciers in the Alps retreated. European winters were milder than the present-day ones. However, due to limitations of the proxy data, quantitative reconstructions are uncertain, especially if they are interpreted in terms of the globally averaged annual mean temperature. While some studies conclude that global temperature in this period was slightly higher than today, others argue that the Medieval climate optimum was limited for the Northern Hemisphere extratropics.
The period following the Medieval warm optimum was colder than this optimum. In the mid-latitudinal and subpolar Eurasia, winters became more severe. In the Alps, the glaciers transgressed again. Sea ice was more abundant, appearing earlier in autumn and withdrawing later in spring in the North Atlantics. According to the presently available data, global temperature in the seventeenth century was lower than that in the mid-twentieth century by about 0.5 °C. This extreme cooling is related to the diminished solar irradiance (the Maunder Minimum). In Europe, the seventeenth and early eighteenth centuries were very dry. There is also evidence that, in the fifteenth to nineteenth centuries, precipitation was diminished in Asia as well. This latter dry anomaly is usually interpreted as a result of changes in the Asian monsoon. Since the seventeenth century, climate gradually warmed, while the mean temperature was below that for the mid-twentieth century. This warming was followed by another cool period at the turn of the nineteenth century, again attributed to the diminished solar irradiance (the Dalton Minimum). This latter cold event was weaker and shorter than that occurred in the seventeenth century. The seventeenth to nineteenth centuries are known as the Little Ice Age (while sometimes this term is extended for the whole interval of thirteenth to nineteenth centuries). However, proxy data for the second part of the last millennium, in the Southern Hemisphere (while limited to the tropics), do not show any substation coldness.
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