Allergies may seem like a minor nuisance, but according to the CDC there are an estimated 50 million Americans living with allergies, and $18 billion is spent every year dealing with the affliction.

From hay fever to sneezing to itchy, watery eyes, all of these symptoms could become heightened as plants begin to produce more virulent pollen. Allergies can also exacerbate asthma and slow down productivity, in addition to that overall miserable feeling.

Last week the National Oceanic and Atmospheric Administration found that carbon dioxide levels had reached a grim benchmark of 400 parts per million (ppm) in the atmosphere compared with about 280 ppm before the start of the industrial age.

Additionally, 2012 was the warmest year on record for the U.S., a full 3.2 degrees warmer than the average 20th century temperature, according to NOAA.

Dr. Jeffrey Demain , an allergist and director of the Allergy Asthma & Immunology Center of Alaska, said the new carbon levels concerned him as he’s seen his patients have more severe reactions from allergies. “I think over the last 20 years, in my opinion we’re seeing more patients with allergies,” said Demain. “And the allergies seem to be very significant.”

Attack of Potent Pollen

In the past 53 years, carbon dioxide levels have risen globally approximately 22 percent. Much has been written about how the rise in greenhouse gases is bad for the environment, but less has been said about how these gases can help some plants flourish. Unfortunately for humans these plants, like poison ivy and ragweed, tend to be irritating or even harmful to our health

A 2005 study found that when ragweed plants, a prime cause of hay fever symptoms in late summer and fall, were exposed to higher carbon dioxide levels they not only produced more pollen, but the grains of pollen were covered with increased numbers of nose-irritating proteins, supercharging the pollen’s allergic properties.

The study subjected ragweed plants in a lab setting to different carbon dioxide levels from three eras — the preindustrial age, the present day and even the end of the 21st century. The study found that the allergen concentrations increased 20 percent from the preindustrial age to today. But they were projected to rise a startling 60 percent by the end of the century.

So the plants might be flourishing in 90 years, but anyone with a ragweed allergy will be miserable.

“They’re growing faster, they’re producing more flowers,” said Dr. Lewis Ziska, a research plant physiologist at the United States Department of Agriculture and one of the study’s authors. “It’s a two-edged sword … the [plants] that are responding have implications for public health.

Double Whammy Allergy Season

Traditionally, allergists break up the year into three distinct seasons. In spring it’s the trees that cause the most problems; summer brings flowering grasses that induce sneezing; and in fall ragweed pollen afflicts allergy sufferers with itchy, watery eyes.

But as temperatures more common for July start showing up in April and May in certain areas of the country, plants react to the weather and not the calendar date. Increased overlap between allergy seasons means more pollen in the air and little relief for people hoping for a break between seasons. “If you have high levels of pollen in the air then [people with pollen allergies] might have a lot of symptoms,” said Demain. “They’re a mess.”

However, even when there are multiple allergy seasons happening at once, allergists say there are things people can do to stave off the worst symptoms. To keep pollen out of the home, experts recommend washing your face and changing your clothes after you arrive home and using a neti pot daily to help flush out irritating pollen grains.

A Milder Winter Might Mean a Miserable Spring

When the weather is warmer and seasons are milder, some plants will be releasing allergy-inducing pollen for longer periods of time.

A 2011 study looked at the length of the ragweed seasons in cities along different latitudes from Georgetown, Texas, to Saskatoon, Canada, over a 14-year period. During that time, nearly all the cities experienced fewer days with frost and longer ragweed seasons.

Cities further north also had statistically larger increases to their ragweed allergy seasons. The population of Saskatoon had to contend with a ragweed season 27 days longer in 2009 than in 1995.

Marooned on an ‘Urban Heat Island’ Means More Sneezing

According to the U.S. Census Bureau, more than 80 percent of Americans currently reside in urban areas. While cities that lack greenery may seem like a safe place for people with pollen allergies, experts say they won’t offer much sanctuary during allergy season.

That is partly because cities often become what scientists call “urban heat islands,” where concrete and pavement soak up heat, resulting in consistently higher temperatures compared with surrounding rural areas. With warmer temperatures and higher levels of carbon dioxide, some allergen-inducing plants can produce more pollen than the same plants located in rural areas.

A 2003 study on allergen levels in Baltimore found more than three times the amount of ragweed pollen in the city compared with the surrounding rural areas.

Also, densely packed urban areas have higher levels of diesel and car exhaust, which can irritate the nose and throat, making allergy symptoms worse.

Rocks and natural debris previously covered by snow are appearing now as the snow line has retreated 590 feet, according to Sudeep Thakuri, a University of Milan scientist who led the research.

The pessimistic view of Earth’s tallest peak was presented during a meeting Tuesday of the American Geophysical Union in Cancun, Mexico.

Researchers said they believe the observed changes could be due to human-generated greenhouse gases altering global climate, although their research has not established a firm connection.

The team reconstructed the glacial history of the area using satellite imagery and topographic maps of Everest and the surrounding 713-square-mile Sagarmatha National Park. Their statistical analysis shows that the majority of the glaciers in the national park are retreating at an increasing rate, Thakuri said.

Small glaciers of less than a square kilometer (about 247 acres), are vanishing fastest, registering a 43% decline in surface area since the 1960s.

Average temperatures have risen about 1 degree Fahrenheit since 1992, according data from the Nepal Climate Observatory stations and Nepal’s Department of Hydrology and Meteorology, the researchers found. Since 1992, precipitation has declined nearly four inches during the pre-monsoon and winter months, they found.

“The Himalayan glaciers and ice caps are considered a water tower for Asia since they store and supply water downstream during the dry season,” said Thakuri. “Downstream populations are dependent on the melt water for agriculture, drinking and power production.”

The topic of glacial melt in the Himalayas has been controversial. Initial reports by the Intergovernmental Panel on Climate Change predicted glaciers in the region would disappear by 2035. Subsequent analysis by the Gravity Recovery and Climate Experiment (GRACE) satellite mission showed that the melt was one-tenth the reported rate, and that some areas were experiencing growth, particularly in the Tibetan plateau.

Research published last year, however, showed that glaciers have been retreating over a 30-year period on the Tibetan plateau. It also showed that areas that depend on snow during regional monsoon seasons are particularly vulnerable to small rises in temperature.

The plateau is of concern because it is the ultimate source of drinking and irrigation water for more than 1 billion people in Asia.

From Hurricane Sandy’s devastating blow to the Northeast to the protracted drought that hit the Midwest Corn Belt, natural catastrophes across the United States pounded insurers last year, generating $35 billion in privately insured property losses, $11 billion more than the average over the last decade.

And the industry expects the situation will get worse. “Numerous studies assume a rise in summer drought periods in North America in the future and an increasing probability of severe cyclones relatively far north along the U.S. East Coast in the long term,” said Peter Höppe, who heads Geo Risks Research at the reinsurance giant Munich Re. “The rise in sea level caused by climate change will further increase the risk of storm surge.” Most insurers, including the reinsurance companies that bear much of the ultimate risk in the industry, have little time for the arguments heard in some right-wing circles that climate change isn’t happening, and are quite comfortable with the scientific consensus that burning fossil fuels is the main culprit of global warming.

“Insurance is heavily dependent on scientific thought,” Frank Nutter, president of the Reinsurance Association of America, told me last week. “It is not as amenable to politicized scientific thought.”

Yet when I asked Mr. Nutter what the American insurance industry was doing to combat global warming, his answer was surprising: nothing much. “The industry has really not been engaged in advocacy related to carbon taxes or proposals addressing carbon,” he said. While some big European reinsurers like Munich Re and Swiss Re support efforts to reduce CO2 emissions, “in the United States the household names really have not engaged at all.” Instead, the focus of insurers’ advocacy efforts is zoning rules and disaster mitigation.

Last week, scientists announced that the concentration of heat-trapping carbon dioxide in the atmosphere had reached 400 parts per million — its highest level in at least three million years, before humans appeared on the scene. Back then, mastodons roamed the earth, the polar ice caps were smaller and the sea level was as much as 60 to 80 feet higher.

The milestone puts the earth nearer a point of no return, many scientists think, when vast, disruptive climate change is baked into our future. Pietr P. Tans, who runs the monitoring program at the National Oceanic and Atmospheric Administration, told my colleague Justin Gillis: “It symbolizes that so far we have failed miserably in tackling this problem.” And it raises a perplexing question: why hasn’t corporate America done more to sway its allies in the Republican Party to try to avert a disaster that would clearly be devastating to its own interests?

Mr. Nutter argues that the insurance industry’s reluctance is born of hesitation to become embroiled in controversies over energy policy. But perhaps its executives simply don’t feel so vulnerable. Like farmers, who are largely protected from the ravages of climate change by government-financed crop insurance, insurers also have less to fear than it might at first appear.

The federal government covers flood insurance, among the riskiest kind in this time of crazy weather. And insurers can raise premiums or even drop coverage to adjust to higher risks. Indeed, despite Sandy and drought, property and casualty insurance in the United States was more profitable in 2012 than in 2011, according to the Property Casualty Insurers Association of America.

But the industry’s analysis of the risks it faces is evolving. One sign of that is how some top American insurers responded to a billboard taken out by the conservative Heartland Institute, a prominent climate change denier that has received support from the insurance industry.

The billboard had a picture of Theodore Kaczynski, the Unabomber, who asked: “I still believe in global warming. Do you?”

Concerned about global warming and angry to be equated with a murderous psychopath, insurance companies like Allied World, Renaissance Re, State Farm and XL Group dropped their support for Heartland.

Even more telling, Eli Lehrer, a Heartland vice president who at the time led an insurance-financed project, left the group and helped start the R Street Institute, a standard conservative organization in all respects but one: it believes in climate change and supports a carbon tax to combat it. And it is financed largely with insurance industry money.

Mr. Lehrer points out that a carbon tax fits conservative orthodoxy. It is a broad and flat tax, whose revenue can be used to do away with the corporate income tax — a favorite target of the right. It provides a market-friendly signal, forcing polluters to bear the cost imposed on the rest of us and encouraging them to pollute less. And it is much preferable to a parade of new regulations from the Environmental Protection Agency.

“We are having a debate on the right about a carbon tax for the first time in a long time,” Mr. Lehrer said.

Bob Inglis, formerly a Republican congressman from South Carolina who lost his seat in the 2010 primary to a Tea Party-supported challenger, is another member of this budding coalition. Before he left Congress, he proposed a revenue-neutral bill to create a carbon tax and cut payroll taxes.

Changing the political economy of a carbon tax remains an uphill slog especially in a stagnant economy. But Mr. Inglis notices a thaw. “The best way to do this is in the context of a grand bargain on tax reform,” he said. “It could happen in 2015 or 2016, but probably not before.”

He lists a dozen Republicans in the House and eight in the Senate who would be open to legislation to help avert climate change. He notes that Exelon, the gas and electricity giant, is sympathetic to his efforts — perhaps not least because a carbon tax would give an edge to gas over its dirtier rival, coal. Exxon, too, has also said a carbon tax would be the most effective way to reduce emissions. So why hasn’t the insurance industry come on board?

Robert Muir-Wood is the chief research officer of Risk Management Solutions, one of two main companies the insurance industry relies on to crunch data and model future risks. He argues that insurers haven’t changed their tune because — with the exception of 2004 and 2005, when a string of hurricanes from Ivan to Katrina caused damage worth more than $200 billion — they haven’t yet experienced hefty, sustained losses attributable to climate change.

“Insurers were ready to sign up to all sorts of actions against climate change,” Mr. Muir-Wood told me from his office in London. Then the weather calmed down.

Still, Mr. Muir-Wood notes that the insurance industry faces a different sort of risk: political action. “That is the biggest threat,” he said. When insurers canceled policies and raised premiums in Florida in 2006, politicians jumped on them. “Insurers in Florida,” he said, “became Public Enemy No. 1.”

And that’s the best hope for those concerned about climate change: that global warming isn’t just devastating for society, but also bad for business.

The chief greenhouse gas was measured Thursday at 400 parts per million in Hawaii, a monitoring site that sets the world’s benchmark. It’s a symbolic mark that scientists and environmentalists have been anticipating for years.

While this week’s number has garnered all sorts of attention, it is just a daily reading in the month when the chief greenhouse gas peaks in the Northern Hemisphere. It will be lower the rest of the year. This year will probably average around 396 ppm. But not for long — the trend is going up and at faster and faster rates.

Within a decade the world will never see days — even in the cleanest of places on days in the fall when greenhouse gases are at their lowest — when the carbon measurement falls below 400 ppm, said James Butler, director of global monitoring at the National Oceanic and Atmospheric Administration’s Earth Science Research Lab in Boulder, Colo.

“The 400 is a reminder that our emissions are not only continuing, but they’re accelerating; that’s a scary thing,” Butler said Saturday. “We’re stuck. We’re going to keep going up.”

Carbon dioxide stays in the air for a century, some of it into the thousands of years. And the world carbon dioxide pollution levels are accelerating yearly. Every second, the world’s smokestacks and cars pump 2.4 million pounds of the heat-trapping gas into the air.

Carbon pollution levels that used to be normal for the 20th century are fast becoming history in the 21st century.

“It means we are essentially passing one in a whole series of points of no return,” said Michael Mann, a climate scientist at Pennsylvania State University.

Princeton University climate scientist Michael Oppenheimer said the momentum in carbon dioxide emissions has the world heading toward and passing 450 ppm. That is the level which would essentially mean the world warms another 2 degrees, what scientists think of as dangerous, he said. That 2-degree mark is what much of the world’s nations have set as a goal to prevent.

“The direction we’ve seen is for blowing through the best benchmark for what’s dangerous change,” Oppenheimer said.

And to see what the future is, scientists look to the past.

The last time the worldwide carbon level probably hit 400 ppm was about 2 million years ago, said Pieter Tans of the National Oceanic and Atmospheric Administration.

That was during the Pleistocene Era. “It was much warmer than it is today,” Tans said. “There were forests in Greenland. Sea level was higher, between 10 and 20 meters (33 to 66 feet).”

Other scientists say it may have been 10 million years ago that Earth last encountered this much carbon dioxide in the atmosphere. The first modern humans only appeared in Africa about 200,000 years ago.

Environmental activists, such as former Vice President Al Gore, seized on the milestone.

“This number is a reminder that for the last 150 years — and especially over the last several decades — we have been recklessly polluting the protective sheath of atmosphere that surrounds the Earth and protects the conditions that have fostered the flourishing of our civilization,” Gore said in a statement. “We are altering the composition of our atmosphere at an unprecedented rate.”

Carbon dioxide traps heat just like in a greenhouse. It accounts for three-quarters of the planet’s heat-trapping gases. There are others, such as methane, which has a shorter life span but traps heat more effectively. Both trigger temperatures to rise over time, scientists say, which is causing sea levels to rise and some weather patterns to change.

When measurements of carbon dioxide were first taken in 1958, it measured 315 ppm. Some scientists and environmental groups promote 350 ppm as a safe level for CO2, but scientists acknowledge they don’t really know what levels would stop the effects of global warming.

The level of carbon dioxide in the air is rising faster than in the past decades, despite international efforts by developed nations to curb it. On average the amount is growing by about 2 ppm per year. That’s 100 times faster than at the end of the Ice Age.

Back then, it took 7,000 years for carbon dioxide to reach 80 ppm, Tans said. Because of the burning of fossil fuels, such as oil and coal, carbon dioxide levels have gone up by that amount in just 55 years.

Before the Industrial Revolution, carbon dioxide levels were around 280 ppm, and they were closer to 200 during the Ice Age, which is when sea levels shrank and polar places went from green to icy. There are natural ups and downs of this greenhouse gas, which comes from volcanoes and decomposing plants and animals. But that’s not what has driven current levels so high, Tans said. He said the amount should be even higher, but the world’s oceans are absorbing quite a bit, keeping it out of the air.

“What we see today is 100 percent due to human activity,” said Tans, a NOAA senior scientist. The burning of fossil fuels, such as coal for electricity and oil for gasoline, has caused the overwhelming bulk of the man-made increase in carbon in the air, scientists say.

The world sent 38.2 billion tons of carbon dioxide into the air in 2011, according international calculations published in a scientific journal in December. China spews 10 billion tons of carbon dioxide into the air per year, leading all countries, and its emissions are growing about 10 percent annually. The U.S. at No. 2 is slowly cutting emissions and is down to 5.9 billion tons per year.

The speed of the change is the big worry, said Pennsylvania State’s Mann. If carbon dioxide levels go up 100 ppm over thousands or millions of years, plants and animals can adapt. But that can’t be done at the speed it is now happening.

“We are a society that has inadvertently chosen the double-black diamond run without having learned to ski first,” NASA climate scientist Gavin Schmidt said. “It will be a bumpy ride.”

Scientific monitors reported that the gas had reached an average daily level that surpassed 400 parts per million — just an odometer moment in one sense, but also a sobering reminder that decades of efforts to bring human-produced emissions under control are faltering.

The best available evidence suggests the amount of the gas in the air has not been this high for at least three million years, before humans evolved, and scientists believe the rise portends large changes in the climate and the level of the sea.

“It symbolizes that so far we have failed miserably in tackling this problem,” said Pieter P. Tans, who runs the monitoring program at the National Oceanic and Atmospheric Administration that reported the new reading.

Ralph Keeling, who runs another monitoring program at the Scripps Institution of Oceanography in San Diego, said a continuing rise could be catastrophic. “It means we are quickly losing the possibility of keeping the climate below what people thought were possibly tolerable thresholds,” he said.

The new measurement came from analyzers high atop Mauna Loa, the volcano on the big island of Hawaii that has long been ground zero for monitoring the worldwide carbon dioxide trend.

Devices there sample clean, crisp air that has blown thousands of miles across the Pacific Ocean, producing a record of rising carbon dioxide levels that has been closely tracked for half a century.

Carbon dioxide above 400 parts per million was first seen in the Arctic last year, and had also spiked above that level in hourly readings at Mauna Loa. But the average reading for an entire day surpassed that level at Mauna Loa for the first time in the 24 hours that ended at 8 p.m. Eastern Daylight Time on Thursday, according to data from both NOAA and Scripps.

Carbon dioxide rises and falls on a seasonal cycle and the level will dip below 400 this summer, as leaf growth in the Northern Hemisphere pulls about 10 billion tons of carbon out of the air. But experts say that will be a brief reprieve — the moment is approaching when no measurement of the ambient air anywhere on earth, in any season, will produce a reading below 400.

“It feels like the inevitable march toward disaster,” said Maureen E. Raymo, a Columbia University earth scientist.

From studying air bubbles trapped in Antarctic ice, scientists know that going back 800,000 years, the carbon dioxide level oscillated in a tight band, from about 180 parts per million in the depths of ice ages, to about 280 during the warm periods between. The evidence shows that global temperatures and CO2 levels are tightly linked.

For the entire period of human civilization, roughly 8,000 years, the carbon dioxide level was relatively stable near that upper bound. But the burning of fossil fuels has caused a 41 percent increase in the heat-trapping gas since the Industrial Revolution, a mere geological instant, and scientists say the climate is beginning to react, though they expect far larger changes in the future.

Governments have been trying since 1992 to rein in emissions, but far from slowing, emissions are rising at an accelerating pace, thanks partly to rapid economic growth in developing countries. Scientists fear the level of the gas could triple or even quadruple before being brought under control.

Indirect measurements suggest that the last time the carbon dioxide level was this high was at least three million years ago, during an epoch called the Pliocene. Geological research shows that the climate then was far warmer than today, the world’s ice caps were smaller, and the sea level might have been as much as 60 or 80 feet higher.

Experts fear that humanity may be precipitating a return to such conditions — except this time, billions of people are in harm’s way.

“It takes a long time to melt ice, but we’re doing it,” Dr. Keeling said. “It’s scary.”

Dr. Keeling’s father, Charles David Keeling, began carbon dioxide measurements on Mauna Loa and at other locations in the late 1950s. The elder Dr. Keeling found a level in the air then of about 315 parts per million — meaning that if a person had filled a million quart jars with air, about 315 quart jars of carbon dioxide would have been mixed in.

His analysis revealed a relentless, long-term increase superimposed on the seasonal cycle, a trend that was dubbed the Keeling Curve. Subsequent research proved it was coming from the combustion of fossil fuels. Charles David Keeling died in 2005.

Countries have adopted an official target to limit the damage from global warming, which by most estimates requires that emissions stop by the time the level reaches about 450. “Unless things slow down, we’ll probably get there in well under 25 years,” Ralph Keeling said.

Yet many countries, including China and the United States, have refused to adopt binding national targets. Scientists say that unless far greater efforts are made soon, the goal of limiting the warming will become impossible without severe economic disruption.

“If you start turning the Titanic long before you hit the iceberg, you can go clear without even spilling a drink of a passenger on deck,” said Richard B. Alley, a climate scientist at the Pennsylvania State University. “If you wait until you’re really close, spilling a lot of drinks is the best you can hope for.”

Climate-change contrarians, who have little scientific credibility but are politically influential in Washington, point out that carbon dioxide represents only a tiny fraction of the air — as of Thursday’s reading, exactly .04 percent. “The CO2 levels in the atmosphere are rather undramatic,” a Republican congressman from California, Dana Rohrabacher, said in a Congressional hearing several years ago.

But climate scientists reject that argument, saying it is like claiming that a tiny bit of arsenic or cobra venom cannot have much effect. Research shows that even at such low levels, carbon dioxide is potent at trapping heat near the surface of the earth.

“If you’re looking to stave off climate perturbations that I don’t believe our culture is ready to adapt to, then significant reductions in CO2 emissions have to occur right away,” said Mark Pagani, a Yale geochemist who studies climates of the past. “I feel like the time to do something was yesterday.”

Under the system, 31 nations slapped emission limits on more than 11,000 companies and issued carbon credits that could be traded by firms to meet their new pollution caps. More efficient ones could sell excess carbon credits, while less efficient ones were compelled to buy more. By August 2008, the price for carbon emission credits had soared above $40 per ton — high enough to become an added incentive for some companies to increase their use of cleaner fuels, upgrade equipment and take other steps to reduce carbon footprints.

That system, however, is in deep trouble. A drastic drop in industrial activity has sharply reduced the need for companies to buy emission rights, causing a gradual fall in the price of carbon allowances since the region slipped into a multi-year economic crisis in the latter half of 2008. In recent weeks, however, the price has appeared to have entirely collapsed — falling below $4 as bickering European nations failed to agree on measures to shore up the program.

The collapsing price of carbon in Europe is darkening the outlook for a greener future in a part of the world that was long the bright spot in the struggle against climate change. It is also presenting new challenges for those who once saw Europe’s program as the natural anchor for what would eventually be a linked network of cap-and-trade systems worldwide.

Carbon “started as the commodity of the future, but it has now deteriorated,” said Matthew Gray, a trader at Jefferies Bache in London and one of a diminishing breed of carbon dealers in Europe. “Its future is uncertain.”

The problems plaguing Europe’s cap-and-trade system underscore the uphill battle for international cooperation in the global-warming fight. After middling progress at various summits, officials from more than 190 countries have been charged with forging a global accord by 2015 aimed at cutting carbon emissions. But critics point to the inability of even the European Union — a largely progressive region bound by open borders and a shared bureaucracy — to come together on a fix for its cap-and-trade system as evidence of how difficult consensus building on climate change has become.

Negotiations to launch a similar system across the United States collapsed in 2010, replaced with a regional approach in which California, for instance, moved forward with its own program. Aided by a boom in cheaper and cleaner shale gas as well as the spread of more renewable energies, including wind and solar, the United States has — like Europe — nevertheless seen a continuing drop in its overall emission levels.

But there are also signs that years of increasing investment in clean energies are ebbing on both sides of the Atlantic. In 2012, overall clean-energy investment in the United States fell 37 percent,to $35.6 billion, compared with a year earlier, according to a new report by the Pew Charitable Trusts. European countries, including green leaders such as Germany, also saw declines, leading analysts to call the problems with the region’s cap-and-trade system that much more troubling.

In the middle of Earth’s largest ocean and already in a warm clime, Hawaii seems like the last place to to worry about global warming. But as the air warms, the oceans are absorbing even more heat and that plays out in climate models that Hiroyuki Murakami, of the University of Hawaii, and his colleagues ran to see if they could tease out Hawaii’s probably future.

They published what they discovered in the May 5 issue of the journal Nature Climate Change.

Right now tropical cyclones with the potential of hitting Hawaii are typically born far east of the islands: off the west coast of Mexico, in a way similar to how North Atlantic hurricanes begin off the northwest coast of Africa.

“Normally the tropical cyclones travel west,” said Murakami. “But they very rarely reach Hawaii.”

The researchers used several different climate models at different spatial resolutions and included a variety of environmental factors to see what robust patterns emerged for storm activity from the year 2075 to 2099. Their results suggest fewer, but stronger cyclones along with a northwestward shift of the typical cyclone track — which would take them more directly toward the Hawaiian islands.

In other words, there is good and bad news: the good news is that there will be fewer tropical cyclones. The bad news is they will be stronger, longer lived, with have longer tracks that and steer more towards Hawaii.

“The Hawaiian Islands are very vulnerable,” said Murakami, which is one reason he wanted to do the research in the first place. Another reason is that previous modeling work had not shown any consistent results.

On the other hand, there is no reason for Hawaiians to worry too much yet. The new study is not the last word on the matter. There are a lot more additional studies that can be done to test how robust Murakami’s conclusions are, said climate scientist Tom Knutson of the National Oceanic and Atmospheric Administration.

“They’ve gone a step in that direction,” said Knutson of Murakami’s and his colleagues’ research. But Hawaii is a small place in a big ocean and nailing down the details is tricky. “When you get down to a smaller scale, things got a lot more uncertain.”

The fever has hit California’s agricultural heartland particularly hard in recent years, with the incidence dramatically increasing in 2010 and 2011. The disease — which is prevalent in arid regions of the United States, Mexico, Central and South America — can be contracted by breathing in fungus-laced spores from dust disturbed by the wind as well as human or animal activity.

The fungus is sensitive to environmental changes, experts say, and a hotter, drier climate has increased the dust carrying the spores.

“Research has shown that when soil is dry and it is windy, more spores are likely to become airborne in endemic areas,” said Gil Chavez, deputy director of the Center for Infectious Diseases at the California Department of Public Health.

Long-standing concerns about valley fever were heightened last week when a federal health official ordered the transfer of more than 3,000 exceptionally vulnerable inmates from two San Joaquin Valley prisons where several dozen have died of the disease in recent years. A day later, state officials began investigating an outbreak in February that sickened 28 workers at two solar power plants under construction in San Luis Obispo County.

Although millions of residents in Central California face the threat of valley fever, experts say that people who work in dusty fields or construction sites are most at risk, as are certain ethnic groups and those with weak immune systems. Newcomers and visitors passing through the region may also be more susceptible.

Nationwide, the number of valley fever cases rose by more than 850 percent from 1998 through 2011, according to the Centers for Disease Control and Prevention. In 2011, there were more than 20,400, with most cases reported in California and Arizona.

She was wrong.

On Aug. 28, 2011, Tropical Storm Irene’s rains swelled the Williams River, smashing dams, flooding homes and carrying off the historic Lower Bartonsville Covered Bridge.

This wasn’t just another 1-in-500-years event happening, a freak occurrence, a one-off event. Rather, experts see it as the new normal across the Northeast, the latest in a series of calamitous weather events occurring because of, or amplified by, climate change.

From valleys staggered by Irene, to coasts battered by Superstorm Sandy, the 24-hour outbursts of rain and snow, or “extreme precipitation,” has increased by 74% in the past six decades there, according to January’s draft of the federal National Climate Assessment report.

Such storms have become the signature of climate change across the Northeast, afflicting older cities and towns built at a time of more modest rainfall. This heavy flooding is undermining aging bridges, eroding roads and overwhelming drainage systems.

USA TODAY traveled to the birch- and maple-dappled hills of Vermont as the third stop in a year-long series to explore places where climate change is already changing lives.

“I grew up here. I live here now,” Hammond says, standing on the gravel road leading to the covered bridge’s crossing. “The bridge has always been here.”

That bridge, and hundreds more like it, were damaged in the storm, along with dams, roads, houses and most everything in sight. Three people died and more than $700 million in damage was sustained in Vermont alone. Before trailing off in Canada, Irene had killed 49 people and caused more than $10 billion in damages in 2011, according to the National Oceanic and Atmospheric Administration (NOAA). That was only a warm-up for last year’s Superstorm Sandy, which delivered even more crippling blows, killing more than 130 people nationwide and causing more than $75 billion in damages.

Hammer blows such as these storms are consistent with climate change’s expected effects on the Northeast, says climatologist Cameron Wake of the University of New Hampshire in Durham.

“It’s not just those two storms,” he says. “We are suddenly seeing many extreme precipitation events, ones that have led to several 100-year floods across the region just in the last 15 years.”

The soggy misfortune of these extreme events has reached well beyond the Northeast. From the Upper Midwest, suffering from recent flooding, to the desert Southwest, where flash floods are more likely even amid sparser rain overall, high-intensity storms are more frequent. But nowhere is the increase as pronounced as in the Northeast, where already-moist air means more extreme, “extreme precipitation.”

The more intense rainfall is a direct impact of warmer air temperatures tied to climate change juicing the weather cycle, according to the federal assessment report. Average temperatures in the region — the home of some 64 million people stretching from Washington, D.C., to Portland, Maine — have increased 2 degrees Fahrenheit in the past century, with most of the increase coming in the past three decades. The increase largely results from heat-trapping carbon dioxide and other greenhouse gases emitted into the air by burning coal, oil and other fossil fuels, boosting temperatures to spur increases seen worldwide in this century.

STORMS CHANGE ‘EVERYTHING’

Amid trees just starting to bud with spring, Vermont’s State Road 121 follows the twisting course of the Saxtons River. Along the way, Timothy Cullenen, who was municipal manager of nearby Rockingham, Vt., during Irene, points out wrecked homes and condemned, covered bridges with sidewalls beaten out and replaced.

“We had roads washed out, people trapped in homes,” Cullenen says, recounting how firefighters had to boat people out of homes inundated by a river suddenly stuffed with battering-ram-size trees and hissing propane tanks with broken valves. The frequency of these storms “changes everything for us, from what size culverts we build, to where people can live,” Cullenen says.

The Northeast averages about 55 inches of rain and snow annually, according to NOAA records. That’s 10% more than just over a century ago.

What’s causing the additional rain? It’s simple. Warmer air causes more evaporation from streams, lakes and seas. Warmer air also holds more moisture. So, when it falls, it really unloads — thus, more extreme storms.

“Increased extreme precipitation in the Northeast is one of the clearest signals of climate change that we can see nationwide,” says climate expert Donald Wuebbles of the University of Illinois in Urbana-Champaign. “It’s not just more rain, but more rain falling in buckets over long periods of time.”

In the hills of the Northeast, heavy rains are funneled into valley streams and rivers, carrying timber and sand downstream. “Bridges become dams when the water rises and this stuff slams into them,” says FEMA historic preservation expert Peter Thomas.

In Irene, ground already saturated with rainwater couldn’t handle the downpour, making flooding more likely. (Rainfall totaled more than 25 inches for much of the Northeast in August and September 2011, compared with about 8 inches normally.)

“Streams and rivers scoured out by floods just become race tracks for the next flood,” Thomas says. “They won’t have as much time to naturally restore themselves if climate change is making floods more common.”

‘OH MY GOD’: BRIDGE CRUMBLES

“I never had been able to see the river from my window in August before,” Hammond says of the day the bridge washed out. All morning, she and her neighbors had walked down to the bridge to see the river rise. Recording a video of the flooding, she captured the terrible creaking of the century-old structure and sight of it unrolling off its abutments into the water below. The wood tumbled in the river for a half-mile.

Hammond’s video and heartfelt, “Oh, my God,” response to the bridge’s disappearance went viral on YouTube, seen by more than a half-million people and shown widely on television. “I had no idea it had gone viral until my sister told me days later, after we got power back,” Hammond says.

The bridge had been in place since 1870. Now its wreckage sits, three rows of timber in Rockingham’s winter gravel dump, joined by stumps, trees and junk pulled from the river by the town at a cost of $450,000.

“We used to have an emergency fund. And then we had an emergency. Now it is gone,” Cullenen says. “But we still might have another emergency.”

CITIES STRUGGLE TO ADAPT

Towns and cities across the Northeast are built for the wrong century — the last one — says civil engineer Paul Kirshen of Climate Solutions New England, a colleague of Wake, the climatologist. “We’ve seen the ‘once in a century’ storm’s water level increase,” he says. Where a storm with a 1% chance of happening every year used to dump 6 inches of water (162,924 gallons per acre), that same storm now delivers 8 inches (217,232 gallons per acre), according to the U.S. Geological Survey.

That means street drains aren’t big enough and wastewater facilities can’t handle floods. Culverts, the large pipes that carry water under roads, are increasingly being washed out across the region, according to a 2009 Journal of Applied Meteorology and Climatology study. Expensive sewer systems built for last century’s specifications are too small to handle the extra water. More cars and more people mean more pavement, which dumps water on towns built in the horse-and-buggy era, instead of letting it soak in.

For cities such as Philadelphia and Exeter, N.H., one solution has been to try “low-impact” development: planting more greenery in a bid to soak up rainwater before it hits the drains. Another change has been “flexible” development, in which reservoirs and seawalls are designed so that additions can be made, if needed. “That’s a total change in engineering,” Kirshen says. “In the past, we built to specifications for now, and walked away.”

A longer-term solution, Wake points out, is “putting less greenhouse gas in the air.”

Depending on future emissions, average yearly temperatures will increase anywhere from 3 to 10 degrees by the 2080s, according to the draft federal National Climate Assessment report.

NEW ENGLAND’S ESSENCE

Standing on the gravel road leading to her Vermont hamlet, Hammond looks at the rebuilt Lower Bartonsville Covered Bridge, its spruce sides gleaming blond in the sunlight, the sawmill scent of fresh-cut wood hanging in the air. The new bridge, built to historical standards, now exceeds its original length by 17 feet to stretch 168 feet across the Williams River. It rests on concrete abutments with pilings driven 40 feet into the ground — not the stone causeways that were undermined in the 2011 flood.

“A covered bridge is part of what New England is, and it connected us to the world,” Hammond says. “Maybe you have to live here to understand it. It really was quite a blow to see it pulled away.”

The new bridge is designed to last 75 years, taking it almost to the end of the century, when it will face a very different New England.

“Unless something happens again,” Hammond says, before walking back to her home.

But it turns out that plants help cool the planet in another way, by releasing tiny particles into the atmosphere that help reflect sunlight back into space.

Yes, it’s true: Plants pass gas. A new study published in the journal Nature Geoscience found that vapors emitted by plants scatter and absorb radiation from the sun, and that they help form cloud droplets that also reflect the sun’s rays.

“Everyone knows the scent of the forest,” said study co-author Ari Asmi, in a press release from the University of Helsinki. “That scent is made up of these gases.”

The scientists measured concentrations plant vapors and other aerosols at 11 different sites around the globe – seven in Europe, two in North America, and the others in Siberia and South Africa – and recorded the temperature. They found that, as temperatures increased, the plants emitted more vapors, effectively responding to the warming by increasing the cooling effect.

So does that mean we are good then? Do the global cooling emissions from plants offset the global warming emissions coming from a Chevy Camaro’s tailpipe?

Not quite. The scientists found that the effect of the increased plant emissions counters only about 1 percent of global warming. “This does not save us from climate warming,” said study co-author Pauli Paasonen, in the press release.

But the plant gasses still might cool things for you locally, especially if you live in a rural, forested area. The study found that, in places where there is little man-made soot in the air, the effect could counteract up to 30 percent of warming.

And this discovery has the potential to improve our understanding of how and why our climate is changing. Aerosols, that is, tiny solid or liquid particles that hang in the air, are one of the least understood aspects of our atmosphere. “Understanding this mechanism could help us reduce those uncertainties and make the models better,” said Paasonen.