For most of the past 10,000 years, global average temperature has remained relatively stable and low compared to earlier hothouse conditions in our planet's history. In 2004 Hans von Storch criticised its statistical techniques, but later accepted that the effect was very small. Thermometer readings around the world have been rising since the Industrial Revolution, and the causes are a blend of human activity and some natural variability—with the preponderance of evidence saying humans are mostly responsible. It shows a general warming in global temperatures. 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. These calculations produce the global average temperature deviations from the baseline period of 1951 to 1980. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. To project future temperatures, the research team used greenhouse gas emission scenarios outlined in the Intergovernmental Panel on Climate Change (IPCC) Climate Change 2007: The Physical Science Basis report, and the authors expect the steep increase to continue through the year 2100 regardless of which one of the emission scenarios from the 2007 report is considered. [17], For information on the description of the, Qualitative reconstruction using historical records, harvnb error: no target: CITEREFBradleyJones1993 (, harvnb error: no target: CITEREFMcIntyreMcKitrick2003 (, harvnb error: no target: CITEREFHuybers2005 (, harvnb error: no target: CITEREFJansen_et_al.2007 (, harvnb error: no target: CITEREFWeart2011c (, harvnb error: no target: CITEREFJonesBriffaOsbornLough2009 (, harvnb error: no target: CITEREFFolland_et_al.2001 (, harvnb error: no target: CITEREFBBC_News,_16_July2004 (, harvnb error: no target: CITEREFPearce2010_pt4 (, harvnb error: no target: CITEREFMasson-Delmotte_et_al.2013 (, Temperature record of the past 1000 years, Intergovernmental Panel on Climate Change, Table of historic and prehistoric climate indicators. Considerable care must be taken in the averaging process; for example, if a certain region has a large number of tree ring records, a simple average of all the data would strongly over-weight that region, and statistical techniques are used to avoid such over-weighting. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. A reconstruction of regional and global temperature for the past 11,300 years. The records used include tree-rings, ice-layers, layers of sediments and rocks, microfossils, the growth of corals and historic documents. The test in science is whether findings can be replicated using different data and methods. Global temperatures remained mostly flat … New model-data comparisons. In the 1960s, Hubert Lamb generalised from historical documents and temperature records of central England to propose a Medieval Warm Period in the North Atlantic region, followed by Little Ice Age. A reconstruction of regional and global temperature for the past 11,300 years. By combining the various archives, the researchers were able to achieve a high temporal resolution - in some cases down to biweekly intervals. The isotopic composition of snow, corals, and stalactites can also be used to infer temperature. Or a cold winter in one area might be balanced by an extremely warm winter in another part of the globe. Arguments against the MBH studies were reintroduced as part of the Climatic Research Unit email controversy, but dismissed by eight independent investigations. But aerosol cooling is more immediate, while greenhouse gases accumulate slowly and take much longer to leave the atmosphere. This article is the second of two articles describing the hottest time periods in Earth’s history.. Over this period the recent instrumental record, mainly based on direct thermometer readings, has approximately global coverage. According to an ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS), the average global temperature on Earth has increased by a little more than 1° Celsius (2° Fahrenheit) since 1880. A five-degree drop was enough to bury a large part of North America under a towering mass of ice 20,000 years ago. It is also a period when many of today’s adults grew up, so it is a common reference that many people can remember. Though there are minor variations from year to year, all five records show peaks and valleys in sync with each other. It is also a period when many of today’s adults grew up, so it is a common reference that many people can remember. [2]The IPCC Fifth Assessment Report (AR5 WG1) of 2013 examined temperature variations during the last two millennia, and concluded that for average annual Northern Hemisphere temperatures, "the period 1983–2012 was very likely the warmest 30-year period of the last 800 years (high confidence) and likely the warmest 30-year period of the last 1400 years (medium confidence)". Afterwards temperatures rose again, first slowly then very rapidly. Otto-Bliesner, B. L., Rosenbloom, N., Stone, E. J., McKay, N.P., Lunt, D.J., Brady, E.C., Overpeck, J.T. 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. Perkins, S. (2013, March 7). They depict how much various regions of the world have warmed or cooled when compared with a base period of 1951-1980. Sparseness of proxy records results in considerable uncertainty for earlier periods.[2]. The paper is freely accessible at 'A global multiproxy database for temperature reconstructions of the Common Era', and it includes links to the datasets. (2013). In the Mann, Bradley & Hughes 1998 and Mann, Bradley & Hughes 1999 CFR reconstructions, principal components analysis was used to combine some of these regional records before they were globally combined.

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