Creating a record of climate change for the last 1000 years is important to put more recent measurements and predictions of future climate change into perspective and to answer the questions of anthropomorphic or man made climate change. People can and do affect the weather, on the smallest scale one can go snow skiing in the Arabian Desert and on a larger scale, filling a valley in West Virginia with fog from industrial activities, creating continent wide dust storms from agricultural practice in America during the 1930s, or influencing rain with cloud seeding. These are weather phenomena, local or short lived events.
The difference between weather forecasting and predicting global climate change are one of scale. The recent claims of global warming are empirically supported by only a few decades of global observation by satellite and about 150 years or less of accurate and complete weather observations. This is a very short time frame when compared to the history of the earth's climate and to determine if extremes in these observations are weather aberrations or foreshadowing of significant climate change one must look at a longer history of a large area.
Geological evidences of glaciation show huge ice sheets covering large portions of land and retreating in cyclic fashion that occur over periods of tens of thousands of years and are a good indicator of climate but do not offer the resolution needed to determine if recent observations fall outside the norm or indicate anthropomorphic causes.
An image of the last one to two thousand years of climate can be built using data from anecdotal accounts of crop production, seasonal rain or drought indicated by tree ring data, snowfall and melt from glacier bore holes, and reports on social events like the Frost Fairs on the river Thames in London. Significant events of the last thousand years of climate history for the northern hemisphere are the Medieval Warm Period from about 950AD to 1250AD, when the Vikings settled Greenland, followed by falling temperatures until the Little Ice Age, 1500AD-1700AD then generally rising until the present. The Medieval Warm Period and Little Ice Age are supported by tree ring data from the western America and Tibet and ice core data from Greenland. It is worthy to note the ice core data from Greenland indicates colder temperatures now than 80 years ago and runs contrary to global warming theories, and tree ring data indicates not temperature but how conducive conditions were for tree growth and is very accurate in terms of determining dates.
The volcanic eruption of Tambora in Indonesia during 1815 was probably the cause of significantly below normal temperatures in the northern hemisphere during 1816 and is credited with New England's Year Without a Summer, indicating how a natural event can have drastic effects on climate.
The current high temperatures being recorded in the northern hemisphere could continue to climb, melting glaciers and causing sea levels to rise or the earth could begin to cool leading us into the next ice age, no one knows yet. But one thing seems certain, the climate will change.