That is the conclusion of a new report by the U.S. National Academy of Sciences (NAS) and The Royal Society, which is the national scientific academy of the United Kingdom. The plain-language report on climate change addresses 20 issues in a question-and-answer format.
Though estimates of the magnitude and regional expression of future change still have important uncertainties, increases in the extremes of climate that can adversely affect natural ecosystems and human activities and infrastructure are expected.
"Anyone who has kids or grandkids has investment in the future, and in the kind of world we're going to leave behind for them," said Lawrence Livermore National Laboratory atmospheric scientist Benjamin Santer, one of the authors of the report. "People understand that we are changing the chemical composition of the Earth's atmosphere. We are no longer innocent bystanders -- we are active participants in the climate system. This report is an opportunity to try and tell people about the science and the likely outcomes, in plain English."
The Earth's average surface air temperature has increased by about 1.4 degrees Fahrenheit since 1900, with much of this increase taking place since the mid-1970s. A wide range of other observations, such as reduced Arctic sea ice extent and increased ocean heat content, and indications from the natural world, such as poleward shifts of temperature-sensitive species of fish, mammals, insects, etc., provide incontrovertible evidence of planetary-scale warming, the report states.
"Climate change is a dividing issue of our times," said Paul Nurse, head of the Royal Society. "Policy decisions are made on the world stage. This is a simple but authoritative account of the major issues of climate change. It's a reliable guide to the science -- a guide that's necessary for an informed debate."
Scientists know that recent climate change is largely caused by human activities. This knowledge comes from an understanding of basic physics, from comparing observations with models and from 'fingerprinting' the detailed patterns of climate change caused by different human and natural influences.
Inez Fung, the U.S. lead author of the report from the University of California, Berkeley, said that even if the emissions of greenhouse gases stopped today, temperatures would continue to rise.
"If greenhouse gas emissions were to suddenly stop, the earth would not cool to preindustrial levels for thousands of years," she said. "The actions of today have long-term effects. Stopping emissions now doesn't mean we can remove the carbon dioxide that is already in the atmosphere. The accumulation of carbon dioxide in the atmosphere causes continued rises in temperatures and sea levels."
As for significant weather events such as the cold snap on the Eastern seaboard this winter, Fung said climate change will continue to be a leading cause. "A warmer atmosphere can hold more moisture so when it rains, there's more rain. Rainfall will be more intense. Heat waves will become more frequent. We expect droughts, when they occur, will be more severe. There will always be cold nights and cold days in this warming trend, but they will be rarer and rarer."
Santer addressed the recent warming "hiatus" that has occurred over the last decade.
"Our expectation was never to see some monotonic warming trend," Santer said. "The planet is going to warm because of gradual human-caused levels of greenhouse gas emissions. We know that is going to happen along with natural variability."
The report concludes that if emissions continue on their present trajectory, without either technological or regulatory abatement, then warming of 4.7 degrees to 8.6 degrees -- in addition to that which has already occurred -- would be expected by the end of the 21st century. The Lawrence Livermore research was funded by the U.S. Department of Energy's Office of Science.
To see the full report, go to NAS.