One of the most influential US science organisations dedicated to studying the Earth and its environment says human influence on the climate is increasing.
The American Geophysical Union has just adopted a new policy position on global warming in which it states its concern over rising greenhouse gas emissions.
The AGU's council says carbon dioxide concentrations may be climbing faster now than at any time in Earth history.
It calls for concerted worldwide study to understand how Earth will change.
"It is virtually certain that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases will cause global surface climate to be warmer," the AGU council statement says.
"The complexity of the climate system makes it difficult to predict some aspects of human-induced climate change: exactly how fast it will occur, exactly how much it will change, and exactly where those changes will take place."
It continues: "In contrast, scientists are confident in other predictions. Mid-continent warming will be greater than over the oceans, and there will be greater warming at higher latitudes.
"Some polar and glacial ice will melt, and the oceans will warm; both effects will contribute to higher sea levels.
"The hydrologic cycle will change and intensify, leading to changes in water supply as well as flood and drought patterns."
The AGU has just finished its fall meeting held in San Francisco. As in previous years, it heard from researchers whose studies strongly support the idea that human influence on climate is real and growing.
One presentation sought to show that humans had been altering the climate for thousands of years, ever since the beginnings of agriculture.
The AGU said it was imperative scientists worldwide participated in climate research. It also called for policy discussions and decision-making "to be based upon objective assessment of peer-reviewed research results".
The AGU is one of a number of leading US scientific organisations which have adopted a position on climate change that challenges US Government policies.
The US Academy of Sciences has also issued similar sentiments to the AGU.
The Bush administration and members of the Republican-led Congress have, however, frequently criticised what they regard as the poor and uncertain science that underpins much of the case for human-induced climate change.
The US has repudiated the Kyoto Protocol designed to mitigate the effects of global warming because it believes America's economic interests would be gravely damaged.
The White House wants greenhouse gas emissions to be cut not by what it calls the "command and control" of Kyoto, but by voluntary action and development of new energy technologies such as hydrogen-powered fuel cells.