As if the public debate about global warming wasn't complex enough, a new field in climate research is coming of age, grabbing media attention and spawning seemingly contradictory headlines.

The work, called attribution research, doesn't challenge the scientific consensus that climate change is happening. Instead, it strives to understand the regional effects of global warming by determining whether increased greenhouse gas levels did—or didn't—cause a particular weather event. But the findings can be confusing. For instance, scientists say that climate change made Hurricane Sandy worse, but that it had nothing to do with historic floods in Thailand. Warming probably didn't cause this year's severe winter storm, Nemo, but it may have supercharged it. It caused some droughts, but not others.

Adding to the confusion is a trend that worries some experts: People on both sides of the climate divide tend to promote only those attribution studies that support their beliefs. Whether a conscious decision or not, this selective use of research is further polarizing the national conversation on climate change, experts told InsideClimate News.

For the first time in human history, concentrations of carbon dioxide in the atmosphere are expected to pass 400 parts per million across much of the Northern Hemisphere in May, according to scientists who study data from the Mauna Loa Observatory, the world's longest-running CO2 monitoring station.

While crossing the 400 ppm mark isn't a "tipping point" that signals climate catastrophe, scientists told InsideClimate News, it is an important symbolic milestone that underscores government inaction on global warming. 

"This is another global emissions target that we've blown past without doing anything," said Jim Butler, director of global monitoring at NOAA's Earth System Research Laboratory. "Stronger storms, droughts, rising seas. We are already seeing the impacts of increased CO2 in the atmosphere ... How much further can we really go?" The NOAA lab operates the Mauna Loa Observatory and dozens of other greenhouse gas monitoring sites across the globe

One month after a 65-year-old ExxonMobil pipeline burst without warning and dumped Canadian tar sands oil in the town of Mayflower, Ark., government investigators and residents are still looking for answers to basic questions about the spill.

When did the pipeline begin leaking? When and how did the oil company find out about it? How quickly did the company act? How much oil spilled from the pipeline's 22-foot-long gash? And what condition was the line in before it ruptured?

The unanswered questions are urgent because they speak to issues of pipeline safety and enforcement as thousands of miles of new and reconfigured pipelines—including the Keystone XL—are being proposed to run across the United States. 

Just a day after roughly one million gallons of heavy Canadian crude oil spilled into Michigan's Kalamazoo River in 2010, the National Transportation Safety Board announced it was launching a formal investigation into the incident. It quickly set up shop in a local hotel and conducted dozens of interviews with pipeline workers, local officials and residents. It did field and laboratory analysis of the ruptured pipeline in its own labs. And its investigators pored over the responsible company’s records to recreate what happened.

After two years of work, the agency released the results of its investigation: The spill was caused by major lapses in safety by Enbridge Inc., the pipeline's owner and operator, and by "weak regulations" for the entire U.S. pipeline network.

The NTSB has taken none of these steps since the March 29 pipeline break in Mayflower, Ark., where an estimated 210,000 gallons of heavy Canadian crude oil spilled into a neighborhood of neat brick houses. In fact, the independent federal agency hasn't investigated any oil pipeline spills since Kalamazoo, even though information about the risks of transporting oil through pipelines is in high demand as thousands of miles of new pipelines—including the Keystone XL—are being proposed.

As residents and local officials of Mayflower, Ark. were scrambling to evacuate homes and protect their treasured fishing lake from a river of heavy oil pouring through their town on Good Friday afternoon, ExxonMobil, the company responsible for the accident, didn't know what was happening.

A 22-foot gash had opened up in its oil pipeline that cut through the Arkansas town, 450 miles from its headquarters in Houston, and the people were in a sudden uproar. In the emergency response, dispatchers called Exxon and informed them of the unfolding disaster, and company employees arrived on the scene an hour after the emergency was first reported to local authorities.

That is the picture that emerges from transcripts of 911 police reports obtained by InsideClimate News from the Faulkner County Sheriff's Office.

Police transcripts show that Jennifer Dement of 50 Starlite Road North was the first to report the oil spill at 2:44 p.m. on March 29.

As severe storms and possibly tornadoes prepare to tear through central Arkansas, workers who are cleaning up an ExxonMobil pipeline break that spilled oil through the town of Mayflower are rushing to lay more boom and safeguard equipment.

Starting early Wednesday, Mayflower and the surrounding region will likely experience damaging winds of up to 40 miles an hour and receive as much as 3 to 4 inches of rain, according to the National Weather Service. There is a high probability of flash floods since vegetation is just beginning to bloom and groundwater levels are high.

Federal meteorologists say the storm front could also spawn a few tornados.

With momentum building for climate policy in Washington for the first time since 2010, environmentalists are going on the offensive to counter skeptics who helped derail global warming legislation in the past.

While their efforts do a good of identifying the formidable strength of organizations that reject the scientific consensus, it is too early to tell if their counter-weapons will have any effect in the climate wars.

The Climate Reality Project, a group overseen by Al Gore, is trying to win over public opinion by getting people to spread accurate global warming science in the comment sections of news stories online, where the battle rages with particular ferocity.

Drought conditions in more than half of the United States have slipped into a pattern that climatologists say is uncomfortably similar to the most severe droughts in recent U.S. history, including the 1930s Dust Bowl and the widespread 1950s drought.

The 2013 drought season is already off to a worse start than in 2012 or 2011—a trend that scientists at the National Oceanic and Atmospheric Administration (NOAA) say is a good indicator, based on historical records, that the entire year will be drier than last year, even if spring and summer rainfall and temperatures remain the same. If rainfall decreases and temperatures rise, as climatologists are predicting will happen this year, the drought could be even more severe.

The federal researchers also say there is less than a 20 percent chance the drought will end in the next six months. 

New national science standards that make the teaching of global warming part of the public school curriculum are slated to be released this month, potentially ending an era in which climate skepticism has been allowed to seep into the nation's classrooms.

The Next Generation Science Standards were developed by the National Research Council, the National Science Teachers Association, the American Association for the Advancement of Science, the nonprofit Achieve and more than two dozen states. The latest draft recommends that educators teach the evidence for man-made climate change starting as early as elementary school and incorporate it into all science classes, ranging from earth science to chemistry. By eighth grade, students should understand that "human activities, such as the release of greenhouse gases from burning fossil fuels, are major factors in the current rise in Earth’s mean surface temperature (global warming)," the standards say.

They're "revolutionary," said Mark McCaffrey, programs and policy director of the National Center for Science Education (NCSE), a nonprofit that defends evolution and climate education and opposes the teaching of religious views as science.

The 26 states that helped write the standards are expected to adopt them. Another 15 or so have indicated they may accept them—meaning climate change instruction could make its way into classrooms in 40-plus states.

It is probably the most influential paper on climate science today. But few outside scientific circles even know it exists.

Though just six pages long, its dense, technical writing makes it largely incomprehensible to non-experts. And yet this paper is transforming the climate change debate—prompting the financial world to rethink the value of the world's fossil fuel reserves and giving environmental activists a moral argument for action.

That's because behind its complicated terminology is a simple question that affects every aspect of society and business: How much time do we have before the burning of fossil fuels pushes the climate system past tipping points? In a worst-case scenario, about 11 years at current rates of fossil fuel use, according to the paper.

"Once you hear the numbers, at least for me, there is no more room for wishful thinking, for speculation or for doubt," said Bill McKibben, founder of the activist group 350.org. Last year, McKibben plucked the science from popular obscurity and used it in a Rolling Stone article and speaking tour to stoke the moral case for carbon controls.  

The paper, "Greenhouse-Gas Emission Targets for Limiting Global Warming to 2C," was published in April 2009 in Nature, the prestigious science journal. It was the work of researchers from Germany, the UK and Switzerland, led by Malte Meinshausen, a climatologist at Germany's Potsdam Institute for Climate Impact.