Summary for Policymakers of the Fourth Assessment Report - Working Group I of the Intergovernmental Panel on Climate Change released
(2 February 2007)
The Working Group I of the Intergovernmental Panel on Climate Change (IPCC) released the Summary for Policymakers in the Fourth Assessment Report (Climate Change 2007: the Physical Science Basis) in Paris today (2 February). Persons interested can download the Summary from this web address http://www.ipcc.ch/SPM2feb07.pdf . The following is a brief account of the Hong Kong Observatory's observations.
Based on new and more comprehensive data, more sophisticated analyses and improved climate simulations, it is very likely that greenhouse gas emissions from human activities had caused most of the global warming observed in the past 50 years.
Past trends in climate change and projected future changes described in this Summary are broadly consistent with those in the previous assessment report (2001), but with reduction in uncertainties. For example, for the two climate elements of most concern to the public, namely temperature and sea level, the following table shows that the two reports are broadly consistent:
||Third Assessment Report (2001)
||Summary for Policymakers of Fourth Assessment Report (2007)|
|Past global temperature change
||Rose by 0.6C in the 20th century
||Rose by 0.74C in 1906-2005|
|Projection of global temperature to the end of 21st century
||The range of likely rise is 1.4-5.8C
||The range of likely rise is 1.1-6.4C (the best estimate being 1.8 - 4.0C)|
|Past global mean sea level change
||Rose at a mean rate of 1-2 mm per year in the 20th century
||Rose at a rate of 1.8 mm per year in 1961-2003, and 3.1 mm per year in 1993-2003. It is unclear whether the recent faster rise is a long-term trend or natural variability.|
|Projection of global mean sea level to the end of 21st century
||The range of rise is 0.09-0.88 m
||The range of rise is 0.18-0.59 m|
The assessments on climate change in Hong Kong made by the Hong Kong Observatory in the past several years remain generally valid. However, when the full report of IPCC with the associated climate model products are released later this year, the Hong Kong Observatory will review the assessments on climate change in Hong Kong. It is expected that the adjustment required would not be substantial.
The Summary indicates that if the global temperature were to rise by 1.9 - 4.6 C and sustains for millennia, complete melting of the Greenland Ice Sheet could occur, leading to a sea level rise of 7 m.
Press releases related to assessments of the climate change in Hong Kong in the past several years can be found at the following web addresses:
2 February 2007 (Friday)