century known as the Little Ice Age. In the "hockey stick controversy", climate change deniers have asserted that the Medieval Warm Period was warmer than at present, and have disputed the data and methods of climate reconstructions. Temperature change in the last 2,000 years According to IPCC Sixth Assessment Report, in the last 170 years, humans have caused the global temperature to increase to the highest level in the last 2,000 years. The current multi-century period is the warmest in the past 100,000 years. The temperature in the years 2011-2020 was 1.09°C higher than in 1859-1890. The temperature on land rose by 1.59°C while over the ocean it rose only by 0.88°C. General techniques and accuracy By far the best observed period is from 1850 to the present day, with coverage improving over time. Over this period the recent instrumental record, mainly based on direct thermometer readings, has approximately global coverage. It shows a general warming in global temperatures. Before this time various proxies must be used. These proxies are less accurate than direct thermometer measurements, have lower temporal resolution, and have less spatial coverage. Their only advantage is that they enable a longer record to be reconstructed. Since the direct temperature record is more accurate than the proxies (indeed, it is needed to calibrate them) it is used when available: i.e., from 1850 onwards. Quantitative methods using proxy data As there are few instrumental records before 1850, temperatures before then must be reconstructed based on proxy methods. One such method, based on principles of dendroclimatology, uses the width and other characteristics of tree rings to infer temperature. The isotopic composition of snow, corals, and stalactites can also be used to infer temperature. Other techniques which have been used include examining records of the time of crop harvests, the treeline in various locations, and other historical records to make inferences about the temperature. These proxy reconstructions are indirect inferences of temperature and thus tend to have greater uncertainty than instrumental data. Most proxy records have to be calibrated against local temperature records during their period of overlap, to estimate the relationship between temperature and the proxy. The longer history of the proxy is then used to reconstruct temperature from earlier periods. Proxy records must be averaged in some fashion if a global or hemispheric record is desired. The "Composite Plus Scaling" (CPS) method is widely used for large-scale multiproxy reconstructions