Nature of Centennial Global Climate Change from Observational Records

Abstract

In order to provide a better benchmark for climate simulation programs, climate data at Global Historical Climatology Network (GHCN) and Global Summary of the Day (GSOD) archived by the National Climate Data Center (NCDC) are used to ascertain the nature of climate change over the last century. After data validation, about 6000 stations are considered globally to determine the change in mean temperature, and about 5000 stations to determine that change in maximum and minimum temperatures. Global nature of temperature and its change are presented separately for January and July. Both maximum and minimum daily temperatures are used in the analysis. Trend of global change in annual precipitation is also reported here. Least square linear regression is used to ascertain the nature of these changes. Global nature of temperatures in both January and July show bimodal distributions, with the geographical region between the tropics in one mode and the region outside the tropic in another mode. The individual distributions of temperatures of both these regions show separate and similar histograms. Results indicate that over the last century, temperature in January increased more than that during July. Furthermore the minimum temperature in each case increased more than the maximum temperature. Ten separate estimates of temperature change are obtained from the data presented here using different methods. Considering all these estimates, the mean rise in temperature during January was 2.19°C, and during July was 1.72°C. The geographical nature of the rise in temperature shows that though it rises in most locations, the temperature also reduces along eastern Asia, some parts of central Russia, along south-eastern Australia, and along the east coast of the United States. Predominant rise in temperature is mostly over Europe, and in the arctic. Change in precipitation shows that though there is significant reduction rainfall globally, rainfall increases along the equator, in areas around the Gulf of Mexico, along eastern Asia, along the western coast of India, and along the eastern coast of Australia.