24 January 2008Dot Earth
Map shows areas in 2007 that were warmer (reds) and colder (blues) than the mean annual temperature from 1951-1980. (Credit: NASA/GISS)The American Geophysical Union, the world’s largest organization representing earth and space scientists, put out a fresh statement on the causes and consequences of recent climate change and possible responses.
It’s available online here, and I’ve posted it below. [UPDATE: A Republican Senate staffer has challenged the value of the statement in a comment below, saying it was done by a small committee and doesn’t reflect the views of the broader membership of the AGU. I added a comment to his, offering to highlight in boldface below either endorsements of the statement or “minority reports” by members of the AGU.]
Human Impacts on Climate
The Earth’s climate is now clearly out of balance and is warming. Many components of the climate system — including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons — are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century.
Global average surface temperatures increased on average by about 0.6 degrees Celsius over the period 1956-2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century. Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained research effort, involving many AGU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate.
During recent millennia of relatively stable climate, civilization became established and populations have grown rapidly. In the next 50 years, even the lower limit of impending climate change — an additional global mean warming of 1 degree Celsius above the last decade — is far beyond the range of climate variability experienced during the past thousand years and poses global problems in planning for and adapting to it. Warming greater than 2 degrees Celsius above 19th century levels is projected to be disruptive, reducing global agricultural productivity, causing widespread loss of biodiversity, and — if sustained over centuries — melting much of the Greenland ice sheet with ensuing rise in sea level of several meters. If this 2 degrees Celsius warming is to be avoided, then our net annual emissions of carbon dioxide must be reduced by more than 50 percent within this century. With such projections, there are many sources of scientific uncertainty, but none are known that could make the impact of climate change inconsequential. Given the uncertainty in climate projections, there can be surprises that may cause more dramatic disruptions than anticipated from the most probable model projections.
With climate change, as with ozone depletion, the human footprint on Earth is apparent. The cause of disruptive climate change, unlike ozone depletion, is tied to energy use and runs through modern society. Solutions will necessarily involve all aspects of society. Mitigation strategies and adaptation responses will call for collaborations across science, technology, industry, and government. Members of the AGU, as part of the scientific community, collectively have special responsibilities: to pursue research needed to understand it; to educate the public on the causes, risks, and hazards; and to communicate clearly and objectively with those who can implement policies to shape future climate.
Adopted by AGU Council, December, 2003Revised and Reaffirmed, December, 2007
The union’s statement is firmer and has more policy prescriptions than the one from 2003. It reflects a growing effort by various scientific institutions to clarify what is uncontroversial about climate change. The Geological Society of America came out with its statement on the issue in 2006. While it is more constrained and cautious — as geologists, with their long timescale view of things tend to be — it also accepts the basics:
The Geological Society of America (GSA) supports the scientific conclusions that Earth’s climate is changing; the climate changes are due in part to human activities; and the probable consequences of the climate changes will be significant and blind to geopolitical boundaries. Furthermore, the potential implications of global climate change and the time scale over which such changes will likely occur require active, effective, long-term planning. GSA also supports statements on the global climate change issue made by the joint national academies of science (June 2005), American Geophysical Union (December, 2003), and American Chemical Society (2004). GSA strongly encourages that the following efforts be undertaken internationally: (1) adequately research climate change at all time scales, (2) develop thoughtful, science-based policy appropriate for the multifaceted issues of global climate change, (3) organize global planning to recognize, prepare for, and adapt to the causes and consequences of global climate change, and (4) organize and develop comprehensive, long-term strategies for sustainable energy, particularly focused on minimizing impacts on global climate. (The rest is at the link above.)
Once again, I’d like to think that these groups’ conclusions on the science, along with the findings of the Intergovernmental Panel on Climate Change, can help bound, at least a little, the comments on Dot Earth on climate science and its implications.
