feature em A Summary of the 2008 Critical Review Prospects for Future Climate Change and the Reasons for Early Action

• Main Author: Michael C. Maccracken
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Climate change; Sea ice
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.174.2727; http://climate.org/PDF/MacCracken-CritReviewSummary-final.pdf

Combustion of coal, oil, and natural gas and, to a lesser extent, deforestation, landcover change, and emissions of halocarbons and other greenhouse gases (GHGs), are rapidly increasing the atmospheric concentrations of climate-warming gases. Past emissions have initiated warming of 0.1–0.2 °C per decade since the 1970s, leading to accelerated loss of snow cover and Arctic sea ice, more frequent occurrence of very heavy precipitation, intensification of severe storms, rising sea level, and shifts in the natural ranges of plants and animals. Warming above pre-industrial levels is already ~0.8 °C, and present atmospheric levels of GHGs will contribute to a further warming of 0.5–1.0 °C, as equilibrium is re-established. Warming has been and will be greater in mid and high latitudes compared to low latitudes, over land compared to oceans, and at night compared to day. As emissions continue to increase, both warming and the commitment to future warming are presently increasing at a rate of ~0.2 °C per decade, with projections that the rate of warming will further increase if emissions controls are not put in place. Such warming and the associated changes are likely to cause severe impacts to key societal and environmental support systems. Present estimates are that limiting the increase in global average surface temperature to no more than 2–2.5 °C above its 1750 value of ~15 °C will be required to avoid the most catastrophic, but certainly not all, consequences of climate change. Accomplishing this will require reducing emissions sharply by 2050 and to near zero by 2100. This can only be achieved if: (1) developed nations move rapidly to demonstrate that a modern society can function without reliance on technologies that release carbon dioxide (CO 2) and other GHGs to the atmosphere; and (2) developing nations act in the near-term to sharply limit their non-CO 2 emissions while minimizing growth in CO