The scientific community at large recognizes global warming as a genuine phenomenon. Dissenters suggest the increased temperatures might be due to natural climate fluctuation-perhaps the higher temperatures are part of the same cycle that caused the Ice Age long ago. But recent research indicates that Earth's natural cycles do not sufficiently account for the temperature increases currently observed.
The Intergovernmental Panel on Climate Change recreated temperature records from the past 150 years by running climate models backwards. Some scenarios only used natural drivers of climate change, such as volcanic ash and solar radiation. Other models included the effects of greenhouse gases from fuel emissions, such as carbon dioxide and methane.
\Unless the greenhouse gases were used in the climate models, [scientists] were unable to generate the warming that has occurred,"" said John Magnuson, UW-Madison professor emeritus of limnology, which isthe study of bodies of fresh water. The data did not support scenarios in which warming had strictly natural causes.
Magnuson, a member of the IPCC, studies the ice records of local lakes. He found that in the past 30 years, rising temperatures have altered the winter season.
""We now have about a month and a half less ice cover on Lake Mendota than we had in the 1800s, and that has not been a smooth line of change,"" Magnuson said. ""Since 1970, the ice period has been declining rapidly."" The ice coverage now averages three months per year, but 150 years ago, it lasted four months.
Magnuson cited the winter of 2000-'01, when a local lake had only 22 days of ice cover.
""There was no ice fishing on Lake Mendota that winter,"" Magnuson said. The problem of sparse ice cover could become more common as climate change persists.
""Recent work suggests that the warming we've experienced to date is only due to carbon dioxide emissions that occurred up to 1960,"" said Galen McKinley, UW-Madison assistant professor of atmospheric and oceanic sciences. ""So even if we were to stop using fossil fuels tomorrow, we would have 40 years more of adjustment.""
""We would see carbon dioxide concentration drop in the atmosphere if we stopped putting it up there, but that process of uptake by the oceans could take up to a thousand years,"" said John Williams, UW-Madison assistant professor of geography. ""We would still see about a degree Celsius of warming over the next 100 years.""
Some scientists are concerned that the media's portrayal of global warming causes lay people to be skeptical that it is occurring, despite the overwhelming evidence and scientific consensus.
""The media often present a balanced debate between scientists, but the number of [scientists] who will say that global warming is not occurring is, in fact, very few,"" McKinley said.
""Often an article will give this consensus equal weight with the thoughts of a couple of climate-change skeptics,"" Magnuson said. ""So while attempting to be fair, the media have given more attention to the skeptics than is deserved from the state of the knowledge.""
