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As of July 2015, no similar study has been conducted on a global basis. * From 1979–2014, the three temperate datasets posted above differed from one another by an annual average of 0.13ºF (0.07ºC).The largest gap between any of the datasets in any year was 0.38ºF (0.21ºC), and the smallest gap was 0ºF/C: * To reconstruct global average temperatures in the era before instrumental measurements were made on a global scale, scientists use proxies that respond to changes in climate, such as the widths of tree rings and certain elements of the geological record, to estimate temperature variations in the past.  * The Intergovernmental Panel on Climate Change (IPCC) is a scientific body established in 1988 by the United Nations and World Meteorological Organization.
global mean temperature changes in past centuries.” The report contains the following graph of average temperature changes in Earth’s Northern Hemisphere, showing higher temperatures at present than at any time in the past 1,000 years.
The following map shows these productivity changes, with green signifying higher vegetation productivity and red lower: Plants need water, light, warmth, nutrition and CO2 to grow.