page_title: Global warming controversy
section_title: Temperature projections
hierarchical_section_title: Global warming controversy / Scientific consensus / Temperature projections
caption_attribution_description: English: Comparison of Models from Ch. 6 of IPCC First Assessment Report (FAR) published in 1990 to current observations. Data from figure 6.11 b. Scenarios as described therein. equilibrium sensitivity used is 2.5 deg C/doubling. IPCC also ran with 4 deg C/doubling and 1.5 deg/doubling. The current best estimate is around 3 deg. C, so the 2.5 deg /doubling is the model used. Notes: BaU=Business as Usual, however it should be noted that business did not go as usual due to the implementation of the montreal protocol which substantially reduced CFC emissions. Added 0.71 to GISTEMP to get "relative to prehistoric." 1975 value for the IPCC predictions was 0.71 and average of GISTEMP from 1970-1980 was less than 0.01 from zero.
context_page_description: The global warming controversy concerns the public debate over whether global warming is occurring, how much has occurred in modern times, what has caused it, what its effects will be, whether any action can or should be taken to curb it, and if so what that action should be. In the scientific literature, there is a strong consensus that global surface temperatures have increased in recent decades and that the trend is caused by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view, though a few organizations with members in extractive industries hold non-committal positions, and some have attempted to convince the public that climate change isn't happening, or if the climate is changing it isn't because of human influence, attempting to sow doubt in the scientific consensus.
  The controversy is, by now, political rather than scientific: there is a scientific consensus that global warming is happening and is caused by human activity.
context_section_description: James Hansen's 1984 climate model projections versus observed temperatures are updated each year by Dr Mikako Sato of Columbia University. The RealClimate website provides an annual update comparing both Hansen's 1988 model projections and the IPCC Fourth Assessment Report (AR4) climate model projections with observed temperatures recorded by GISS and HadCRUT. The measured temperatures show continuing global warming.
  Conventional projections of future temperature rises depend on estimates of future anthropogenic GHG emissions (see SRES), those positive and negative climate change feedbacks that have so far been incorporated into the models, and the climate sensitivity. Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100. Others have proposed that temperature increases may be higher than IPCC estimates. One theory is that the climate may reach a "tipping point" where positive feedback effects lead to runaway global warming; such feedbacks include decreased reflection of solar radiation as sea ice melts, exposing darker seawater, and the potential release of large volumes of methane from thawing permafrost. In 1959, Dr. Bert Bolin, in a speech to the National Academy of Sciences, predicted that by the year 2000, there would be a 25% increase in carbon dioxide in the atmosphere compared to the levels in 1859. The actual increase by 2000 was about 29%.
  David Orrell or Henk Tennekes say that climate change cannot be accurately predicted. Orrell says that the range of future increase in temperature suggested by the IPCC rather represents a social consensus in the climate community, but adds "we are having a dangerous effect on the climate".
  A 2007 study by David Douglass and coworkers, concluded that the 22 most commonly used global climate models used by the IPCC were unable to accurately predict accelerated warming in the troposphere although they did match actual surface warming, concluding "projections of future climate based on these models should be viewed with much caution". This result went against a similar study of 19 models which found that discrepancies between model predictions and actual temperature were likely due to measurement errors.
  In a NASA report published in January 2013, Hansen and Sato noted "the 5-year mean global temperature has been flat for a decade, which we interpret as a combination of natural variability and a slowdown in the growth rate of the net climate forcing." Ed Hawkins, of the University of Reading, stated that the "surface temperatures since 2005 are already at the low end of the range of projections derived from 20 climate models. If they remain flat, they will fall outside the models' range within a few years." Using the long-term temperature trends for the earth scientists and statisticians conclude that it continues to warm through time.
caption: IPCC AR4 projections compared to the GISS temperature record[176]
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