| Abstract |
In 2007, the fourth major assessment of technical information on climate change by the Intergovernmental Panel on Climate Change (IPCC) was published in November. The year also saw continued release of new scientific findings on various aspects of climate change. The IPCC Fourth Assessment Report (AR4) critically reviewed the research on science, impacts, and mitigation strategies, and underscored large areas of agreement on climate issues (as well as some important uncertainties and disagreements). The IPCC concluded that the Earths climate unequivocally has warmed over the past century, and that while natural factors, including changes in solar irradiance and volcanoes, have played roles in the observed changes, most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. Additional research published in 2007 showed continuously rising concentrations of greenhouse gases and temperatures, record loss of Arctic sea ice in the summer, transit by sailboat through the legendary Northwest Passage through the Arctic, and other markers of climate change. Additional research indicated several ecological risks including mortality of the eastern Pacific gray whale and lower survival rates among young polar bears linked to climate change. Concerns about climate change are based both on observed changes to date and projections of what is likely to occur in the future. The IPCC concluded that greenhouse gas emissions and concentrations in the atmosphere could be expected to grow through the 21st Century in the absence of concerted climate change mitigation policies. For a wide range of plausible GHG scenarios to 2100, the IPCC projected best guess increases in global average temperatures from 1.8oC to 4.0oC (3.2oF to 7.2oF). Its range of all scenarios to 2100, incorporating a fuller range of uncertainties, was 1.1oC to 6.4oC (2.0oF to 11.5oF). Associated with the projections are impacts that may be beneficial in some locations and for some sectors with small changes in globally averaged climate, but that would be adverse for others, particularly in regions that are already warm and dry, and may become more so. Adverse effects are expected to multiply with accumulating climate change. Sea levels could rise between seven and 23 inches by 2100, not including the effects of possible accelerated melting of the Greenland or Antarctic ice sheets. The risks of abrupt and irreversible changes in the climate system some potentially catastrophic continue to grow as the atmosphere moves further from its state over the past several thousand years. |
