Too alarmist, or too conservative? Both questions are being asked about a U.N. report on climate change that warns of impacts ranging from flooded coastlines to food shortages and species extinction.
The short answer: It depends on your perspective — and more precisely, how you weigh risk and potential impacts. That's the focus of the Intergovernmental Panel on Climate Change's latest report, which runs to more than 1,000 pages, as well as a 44-page summary for policymakers.
Like previous IPCC studies, the report issued on Monday is a lightning rod. Some say the panel's long, laborious process makes the final product out of date and too weak. Others say the summaries that are produced for policymakers exaggerate the risks. This time, those critics include one of the report's lead authors.
"I took my name off the summary for policymakers because it is too alarmist," said Richard Tol, an economist at Britain's University of Sussex who was a lead author of the report's chapter on economics.
This week's report doesn't try to project how much sea levels will rise, or which areas will dry up. Those issues were addressed in an earlier study. Instead, scientists focused on how to manage the risks. Charts in the report show the risks and adaptation potential for global regions — and then provide a range for each risk, from very low to very high.
The full report cites estimates suggesting that the cost of adapting to global climate change could amount to as much as $100 billion a year by 2050 — but adds that "there is little confidence in these numbers." Such uncertainty adds to the challenge of assessing future risks.
Risk assessment is a feature that wasn't part of the panel's previous report on impacts and adaptation, issued in 2007. The point of the exercise is to show that risks can be reduced or increased by taking steps (or not taking steps) to mitigate or adapt to a global warming trend.
Establishing the risks is no easy task for one scientist, let alone for the 309 scientists from 70 countries who wrote the report.
The IPCC's work — which won it the 2007 Nobel Peace Prize — is a lengthy, peer-reviewed process whose critics usually come from conservative groups that question the science and oppose intervention by governments.
Tol provided fodder for the skeptics by withdrawing from the subgroup that drafted the summary for policymakers. He told NBC News that he believes the summary magnifies negative impacts while "downplaying positive impacts."
It also "fails to emphasize that many of the worst impacts of climate change are in fact symptoms of bad management and underdevelopment," he added.
Tol earlier told the BBC "the message in the first draft was that through adaptation and clever development these were manageable risks. ... This has completely disappeared from the draft now, which is all about the impacts of climate change and the Four Horsemen of the Apocalypse."
"You have a very silly statement in the draft summary that says that people who live in war-torn countries are more vulnerable to climate change, which is undoubtedly true," Tol added. "But if you ask people in Syria whether they are more concerned with chemical weapons or climate change, I think they would pick chemical weapons."
Chris Field, a co-chair of the report group and director of the Carnegie Institution's Department of Global Ecology, told NBC News that he had tried to get Tol "to stay on board so that his opinions could be accurately reflected" in the summary.
In any case, Field said, "the reality is that every author thinks the report would be better if it focused more on his or her own work. But our job is to reflect the full range of views, including the strengths and weaknesses of each."
Others felt the report was conservative.
"I think it understates some of the cases," Kevin Trenberth, a senior scientist at the U.S. National Center for Atmospheric Research, told NBC News. "There is not very much about drought, and water resources, anywhere. It seems to me that was given short shrift."
Jim White, director of the Institute of Arctic and Alpine Research at the University of Colorado, said the IPCC process is too slow to factor in the latest research on sea-level rise from melting ice sheets. He cited recent studies on West Antarctica and Greenland "that show that ice loss is accelerating faster than expected — which would lead to higher than expected sea-level rise than the IPCC shows."
For Trenberth, both the IPCC and the news media have room to improve when it comes to reporting on climate change. "A report every six years is not enough. An annual report at least is needed," he said of the IPCC update.
"The media," he added, "has generally under-reported the IPCC work. One shot and done, yet it is a continuing major issue that disappears for weeks."
The remaining scientific uncertainties — and there are plenty of them — help explain the IPCC's slow pace, the media's shifting interest level and even wavering efforts by governments to intervene.
Linda Mearns, a National Center for Atmospheric Research scientist who is one of the report's authors , has studied the role of uncertainty in decision making.
"The fact that we can't tell now exactly how much temperature will increase in Kansas City by 2050 is not a reason to do nothing," she said. "People make decisions under conditions of uncertainty all the time, and most people realize this — I hope."
Field noted that society already has started adapting to reduce the risks. But, he added, so far most of that adaptation has been reacting to past events instead of preparing for what's likely to be an even warmer future.
So is the report an apocalyptic prediction of certain misery ahead, or is it a guidebook for managing the risks rather than waiting for things to get worse?
"Perhaps it is best to call the report a bit of both," Field told NBC News. "At least a couple of horsemen are on the horizon, but there is a lot we can do."