By Marianne Lavelle for The Daily Climate

The new National Climate Assessment's key message is to analyze climate change as it stands now — not to focus on the future.

Most climate reports, with their heavy reliance on projections, cast the problem into the future. The 1,300-page report, unveiled by the White House today (May 6), focuses instead on changes well underway.

The work of some 300 scientists over four years, the report details impacts in every corner of the nation: from Iowa corn production, to Washington State oyster farming, to Vermont maple syrup production.

"We’ve seen a lot in the last five years," said Andrew Rosenberg of the Union of Concerned Scientists (UCS), one of the lead authors on the report’s oceans chapter. "So what we’ve tried to do is be quite comprehensive on what our observations have been, as opposed to just modeling projections."

The oceans chapter is a good example of how increased evidence makes this report far more concrete than the last national assessment, released in 2009, or the more widely known reviews by the Intergovernmental Panel on Climate Change, also published every five or six years, he noted.

"Five years ago, ocean acidification and species movement was already happening, but the observational record wasn’t as clear," Rosenberg said. "Now it really is quite clear. It’s not theory-based or model-based."

Scientists have enough evidence to illustrate the complexity of the impacts communities are facing, said Eugene Takle, director of the climate science program at Iowa State University and an author of the agriculture chapter.

For example, farmers are planting earlier because the winters are shorter in the Midwest, he said. "But they are facing more extreme rain events, so that’s accompanied by narrower windows to get the crops in."

"It’s a two-edged sword," he added. "In some ways it’s better for agriculture, but you are also seeing increasing negative effects that limit production."

In Takle’s view, the report is a summing up of "choices, opportunities, and examples of strategies that do, in fact, work."

Under a law passed by Congress in 1990, a national assessment on climate change is due every four years. But only two previous reports have been completed – one at the end of President Bill Clinton’s administration in 2000, and one at the start of President Barack Obama’s administration in 2009.

The report's value, said Leonard Berry, director of the Florida Center for Environmental Studies, is its ability to translate the global picture into "more meaningful local impacts."

"What it can do, and will do, is bring it down to Earth and a place we all know and understand," said Berry, an author on a chapter on Southeast impacts.

Rosenberg, who also directs UCS' Center for Science and Democracy, said he was struck by how many different fields of science were engaged in the effort to develop the most comprehensive assessment of U.S. climate impacts to date. "The public perception is that there are some people who work on climate. But now, everything is a climate-related field," he said. "If you are working on human health, fisheries, forestry – all these disciplines have to be done now in light of a changing climate."

That consensus is significant, said another report author, Donald Wuebbles, an atmospheric scientist at the University of Illinois.

"A lot of really smart people, all looking at this from different angles, are all saying that this is something you ought to be paying attention to."

Marianne Lavelle is a science reporter for the Daily Climate, a nonprofit news service covering energy, the environment and climate change.

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This story was originally written for The Daily Climate and was republished with permission here.