NOAA

Concentrations of the greenhouse gas carbon dioxide in air sampled at Mauna Loa Observatory in Hawaii will likely peak above 400 ppm this month, scientists said.

Any day now, the concentration of the greenhouse gas carbon dioxide sampled from the air wafting above a barren lava field in Hawaii could be above 400 parts per million (ppm), a level not seen since the Pliocene, between 3.2 and 5 million years ago.

Carbon dioxide levels were around 280 ppm when the Industrial Revolution got under way in the 18th century and humans started pumping greenhouse gases into the atmosphere from burning fossil fuels. Levels have continued to accelerate higher since then.

Hitting the 400 ppm milestone is symbolic to science and policy discussions about efforts to control global climate change, according Ralph Keeling, a geochemist at the Scripps Institution of Oceanography in La Jolla, Calif. 

Human-forced global climate change is primarily driven by rising concentrations of carbon dioxide. Round numbers such as 350 ppm, 400 ppm and 450 ppm are discussed as targets for "safe" levels of the greenhouse gas - a level that will prevent the climate from spinning out of control, he explained.

"So crossing 400 represents, if you will, a lost opportunity," Keeling said.

His late father, Charles David Keeling, a climate science pioneer at Scripps, began tracking levels of carbon dioxide in 1958 at the Mauna Loa Observatory. Concentrations then were 316 ppm. 

Since then, levels have continued to step higher in a saw-tooth pattern, peaking each May before drifting lower as plants in the Northern Hemisphere absorb carbon dioxide to grow, then rising in the fall and winter.

Keeling Curve
The readings plotted on a graph show carbon dioxide concentrations curving sharply higher over time as humans burn more and more fossil fuels. The graph is known as the Keeling Curve. 

Details from the curve, in fact, show the rate of increase continuing to accelerate, noted Pieter Tans, the senior scientist at the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostic Lab, which oversees the Mauna Loa Observatory.

Scripps Institution of Oceanography

The saw-tooth graph, known as the Keeling Curve, shows rising concentrations of the greenhouse gas carbon dioxide in the atmosphere since record keeping began in 1958.

When David Keeling first started keeping records, the five-year average rate of change was 0.7 ppm. Today, it is 2 ppm, more than three times faster, he said. 

"That is significant," Tans told NBC News. "We are just mostly talking about decreasing emissions. In practice, at least globally average, emissions are still accelerating and so is the rate of CO2 increase in the atmosphere."

But crossing 400 ppm in and of itself "doesn't mean anything in particular," Daniel Sarewitz, a sustainability scientist at Arizona State University, noted in an email to NBC News. "It's just another indicator of what we know full well already — that modern society is enormously dependent on fossil fuels for its well-being."

And that dependence on fossil fuels means concentrations of carbon dioxide will continue to climb for the foreseeable future, he added.

Watching for 400
To mark the crossing of 400 ppm, Scripps Institution of Oceanography launched a website and Twitter feed to provide daily readings from Mauna Loa. As of this writing, it stands at 399.29.

The hourly number fluctuates up and down depending on the atmospheric winds and, to a lesser extent, pockets air that upwell from lower on the island. Scientists calculate a daily average from hourly readings (when there's too much noise, a reading isn't produced). The daily numbers are then averaged to establish weekly, monthly and yearly numbers to be plotted on the graph.

From a scientific point of view, the monthly number matters the most, said Ralph Keeling, who took over the record keeping from his father. It is unlikely that this May will actually have an average above 400 ppm. The month is already a few days old and the threshold hasn't been crossed yet. The peak is typically the middle of the month.

There is, however, a better-than 50-50 chance that at least one daily reading above 400 will be recorded in the next few weeks, he said.

"Of course, we might go the whole month without it, but I'd be very surprised if we don't creep up over 400 next May and in a matter of a couple years, even the trough in the cycle will climb over 400, so it will be very hard to find any air that is below 400," he added.

How high concentrations will eventually go, he added, largely depends how willing humans are to forgo burning available reserves of fossil fuels and how many of those fuels actually exist.

"We are starting to move toward alternate fossil energy — non-conventional fossil fuels like tar sands and so forth," Keeling said. "And that’s a little troubling because it reflects our willingness to expand and use reserves of fossil fuels that probably ought to stay in the ground if we take this problem seriously."

John Roach is a contributing writer for NBC News. To learn more about him, visit his website.

NASA / NOAA

This file NOAA's GOES-13 weather satellite image shows the storm system associated with Superstorm Sandy covering the northeastern United States before landfall.

Six months after Superstorm Sandy killed dozens of people and caused an estimated $50 billion in damage on the East Coast, a majority — 58 percent — of Americans see a connection between recent changes in the weather and global climate change, according to a new report.

"People are beginning to recognize a pattern of extreme weather across the country and are themselves saying 'Aha, I wonder if climate change has something to do with that,'" Anthony Leiserowitz, director of the Yale Project on Climate Change Communication, which released the report today, told NBC News.

About half the country, he added, believes climate change is affecting specific extreme weather events. For example 50 percent linked climate change to the record warmth in 2012, 49 percent to the ongoing drought in the Midwest and Great Plains, 46 percent to Superstorm Sandy, and 42 percent to Superstorm Nemo.

Climate scientists are typically careful not to draw too close of an association between climate change and the day-to-day weather, notes Leiserowitz. The standard talking point is that no single weather event is caused by climate change. Still, climate change may be making the usual weather worse.

"The report provides good evidence for why it is we rely on science rather than public opinion on such matters," Roger Pielke Jr., from the Center for Science and Technology Policy Research at the University of Colorado, said in an email to NBC News. Pielke was not involved with the Yale survey, but has written extensively on climate change policy.

"The attribution of changes in climate on extremes is a difficult and thorny scientific puzzle requiring long-term data," he added. "Unfortunately, the human experience — in one place at a time and over a generation — is not a solid basis for such attribution."

In recent years, however, climate science has evolved to the point where some researchers are beginning to see the fingerprint of climate change on individual heat waves, droughts, hurricanes, and other storms.

Read: Blame blistering heat waves on global warming, study says

These so-called attribution studies calculate the likelihood that events such as the Russian heat wave of 2010 and the drought in Texas and Oklahoma in 2011 could have occurred in the absence of climate change. 

The answer is "very, very small ... so that basic line has begun to shift even among the climate science community," Leiserowitz said.

The American people, he added, "are not empty vessels waiting to be told to think about these issues by scientists or journalists, they are actively interpreting their own experience and what we are seeing in our data is that many Americans are now connecting the dots."

The connections the public is drawing between extreme weather events and climate change are consistent with the climate science, Leiserowitz said. While climate change doesn't necessarily cause the weather events, adding greenhouse gases to the Earth's weather system has an effect similar to giving steroids to a baseball player: Harder hits. It juices the system, he said.

And the picture the connected dots present shows climate change making life harder — about two out of three Americans said the weather has been "worse" over the past couple years, which is up 12 percentage points from 2012. Only 11 percent said the weather has gotten better, down 16 points.

In addition, just over half believe extreme weather will cause a natural disaster in their community in the next year.

That said, only one in three Americans are actually prepared for an extreme weather event, highlighting the need for people to develop an emergency plan and kit and get "ready for the unknown event that is going to happen in your lifetime at some point," Leiserowitz said.

The survey is based on interviews with 1,045 adults between April 8 and 15 with a margin of error of +/- 3 percentage points.

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. 

Darrell S. Kaufman / Northern Arizona University

Kristi Wallace of the Alaska Volcano Observatory examines a lake sediment core from southern Alaska that shows intricate layering indicating environmental and climatic changes over centuries.

A long-term global cooling trend ended in the late 19th century, a reversal in temperature that cannot be explained by natural variability alone, according to a new study.

The finding stems from 2,000-year-long continental-scale temperature records inferred from tree rings, ice cores, lake sediments and other so-called proxies from around the world. 

The records show variations in temperature caused by changes in Earth's orbit, output of solar energy, and volcanic eruptions, noted Nicholas McKay, a climate scientist at Northern Arizona University and study co-author. Volcanic eruptions, for example, inject particles in the atmosphere that reflect some of the solar radiation back out to space.

Read: Warming fastest since dawn of civilization, study shows

"The 18th and 19th centuries would probably have been colder than the 20th century no matter what just because there has been a bit less volcanism in this century, but the amount of warming we've seen is extremely unlikely to have happened solely due to natural processes," he told NBC News.

In fact, he and colleagues note in the study — published Sunday in Nature Geoscience — that the natural factors that drove the Earth's long-term cooling are still present today, despite the fact that we are in a period of rising global temperatures.

The "hockey stick"
The record is consistent with other recent temperature reconstructions that show the reversal in long-term cooling coinciding with the acceleration of greenhouse gas emissions from human activity during the industrial revolution at the end of the 19th century.

Gerald North, a climate scientist at Texas A&M University, told NBC News in an email that the new study seems to fit the emerging consensus of a gradual cooling of the past 1,000 to 2,000 years followed by "an abrupt warming since 1900."

"Each year we have more evidence corroborating these same findings," he said. "It is 15 years since the first paper ... known as the 'hockey stick' paper. We have no credible evidence that they got it wrong."

The researcher behind the iconic 1999 "hockey stick" graph, Pennsylvania State University climate scientist Michael Mann, was not part of the new study, but he told NBC News in an emailed statement that the work of McKay and his team "adds to the growing body of scientific evidence that the recent warming is likely unprecedented even further back in time."

Mann added, "While the study doesn't attribute causality to the warming, there is an extensive body of research that shows that we can only explain the anomalous recent warming with human impacts, i.e. burning of fossil fuels and resulting increase in greenhouse gas concentrations."

Regional temperature variations
One distinguishing feature of the new study, noted McKay, is that it highlights variability in temperature around the globe at any one time. For example, a rise in temperatures known as the Medieval Warm Period followed by cooling during the Little Ice Age was pronounced in Europe and North America, less so in the Southern Hemisphere, he said.

While the paper isn't the first to look at regional climate reconstructions, it is the first so well organized, noted David Anderson, a paleoclimatologist with the National Oceanic and Atmospheric Administration's National Climatic Data Center. And, collectively, the regions show the end to the cooling trend on a global scale. "It is truly no debate," he told NBC News.

The ability to see the regional variability in response to forces on the global climate — from human burning of fossil fuels to volcanic eruptions — will be increasingly important as humans try to mitigate and adapt to future climate change, McKay added.

John Roach is a contributing writer for NBC News. To learn more about him, visit his website.

John Brecher / NBC News

An array of 575 solar panels covers the roof of the Bullitt Center, a role model for a new generation of sustainable, energy-efficient buildings.

In cloudy, drizzly Seattle, Denis Hayes, the environmental activist who organized the first Earth Day in 1970, is pulling the wraps off a six-story office building that generates all of its electricity via an oversized rooftop array of solar panels.

A sun-powered building in Seattle is "formidable," Hayes told NBC News, but the Bullitt Center project aims to show it is possible in a visible, tangible manner that, in turn, makes an impact on the often invisible, slow-motion challenge of global climate change.

"When this whole [Earth Day] thing got launched in 1970, we had people walking around with gas masks and smokestacks were pouring out enormous impenetrable clouds of black smoke," said Hayes, who is now president of the Bullitt Foundation, which supports environmental causes.

Today, the sooty smokestacks and black clouds are largely gone, but our energy demands have never been greater, and the impacts of climate change are considered by environmental advocates to be more and more apparent, ranging from extreme weather to growing food insecurity. As scientists toil to identify how our world is changing, the environmental movement will have to spend the next decades finding better ways to rally the world's citizens to address the new challenges.

Self-sustaining architecture
Hayes says the Bullitt Center addresses many of the environmental issues underpinned by global climate change. Take, for example, the building's 56,000-gallon basement cistern for storing captured rainwater. It's a seemingly odd fixture for a building in a city famous for its rain and amply supplied by water, stored in snow form, from the nearby Cascade Mountains.

Slideshow: A look at the world's greenest office building

John Stamets

The Bullitt Foundation, whose mission is to safeguard the environment, spent $18.5 million to construct this uniquely sustainable office building.

Launch slideshow

"There is not going to be enough water in the future," Hayes said. "There is going to be far less snowpack. The water is going to come in gushers and there is just no way to build additional reservoirs to capture it in the Cascades."

John Brecher / NBC News

Hayes, who co-founded Earth Day with Gaylord Nelson, now heads the Seattle-based Bullitt Foundation.

The solution? Build thousands of reservoirs in the basements of buildings, sufficient to hold water to meet the needs of the current and future residents of a city that studies suggest could grow by at least a million people in the next few decades — potentially, many climate refugees from the parched Southwest, noted Hayes.

The hope is that "by trying to build a building as best we could, that literally does everything right," the Bullitt Center will drive change in the building industry with the type of impact Tom's of Maine, a green personal care products company, had on Proctor and Gamble, an industry giant, Hayes said.

Given that buildings in the U.S. account for 39 percent of the nation's carbon dioxide emissions, 65 percent of waste and 70 percent electrical use, adoption of the Living Building Challenge standards highlighted by the Bullitt Center could make life on Earth more sustainable by the middle of this century.

"If we can get a whole bunch of these other buildings built and we start eating up that market share, then we can begin to have changes that are not small incremental one inch here, five inches there, but a fairly profound impact," he explained. "At least, that's the theory."

Want to know more about the Bullitt Center? Read our feature story here, and check out our slideshow.

Rising food insecurity
But even if self-sustainable architecture really takes off, it can't solve all the environmental issues, Hayes noted. In particular, he worries about food security, at a time when rising prosperity around the world means a shift to more meat-heavy diets. 

The shift in diet is not the only issue, either. It may be hard enough to meet the basic needs of a hungry population, according to Lester Brown, founder and president of the Earth Policy Institute and a leading thinker on global environmental issues.

"Agriculture as it exists today has evolved over an 11,000-year period of rather remarkable climate stability," he told NBC News. "If the climate system begins to change, suddenly the climate system and the agricultural system will no longer be in sync with each other. With each passing year, they will be more and more out of sync, making it difficult to just maintain production, much less to increase it."

The solution, Brown added, would be to escalate the problem from the agriculture departments and ministries up to the very heads of state, who will need to grasp food's relationship to everything from energy policy to shifts in population.

And in turn, world leaders need to work together. 

"No one country can ensure food security on its own because we are talking about climate change being one of the keys here and that requires a global effort," Brown explained. "No country can stabilize its climate unilaterally; it takes a concerted international effort."

Rousing international cooperation
Building an international coalition to tackle global climate change is plausible, and happening, leading environmental scientists said Thursday during a panel discussion with recipients of the Tyler Prize, an environmental achievement award, at the National Press Club in Washington, D.C.

For example, John Holdren, director of the White House Office of Science and Technology and a Tyler Prize laureate in 2000, said that in both India and China "the leadership is fully aware of the damage already being done to their countries by climate change and they are fully aware that ultimately the problem cannot be solved without their participation."

That participation, he added, is already underway, as exhibited by a Joint U.S.-China Statement on Climate Change posted on the Department of State's website earlier this month.

"Forceful, nationally appropriate action by the United States and China — including large-scale cooperative action — is more critical than ever," reads the statement. "Such action is crucial both to contain climate change and to set the kind of powerful example that can inspire the world."

Only time will tell if the statement is truly the beginning of something focused and concrete that puts the world on the path to tackling the biggest environmental issues of today and tomorrow.

Meanwhile, Hayes, on the 43rd anniversary of the first Earth Day rally, readies his new self-sustaining office building for the world to see, as he continues to search for ways to raise awareness about the environment.

"Somehow we have to take all of these issues — and I don't have the magic formula — and make them the most immediate concern," he said. "And I guess the reason for optimism is that sometimes stuff just happens. It is almost like a school of fish — it is a biological phenomenon."

John Roach is a contributing writer for NBC News. To learn more about him, visit his website.

Aquamarine Fukushima

An African coelacanth, photographed using a Remotely Operated Vehicle off the coast of Tanga, Tanzania.

The genome of the coelacanth, an ancient-looking lobed-finned fish, has been sequenced and is already providing insight to the evolutionary changes that allowed the first four-limbed animals, called tetrapods, to crawl out of the water and on to land.

The sequence and preliminary analysis, reported Thursday in the journal Nature by a team spanning 40 research institutions and 12 countries, is a "massive piece of work," Xiaobo Xu, a paleontologist at Kean University who was not involved in the effort, told NBC News in an email.

"The paper really provides rare and valuable genomic data for offering heavy-weight opinions on issues bearing on the fish (to) tetrapod transition," he said.

It also settles a debate that has long raged amongst evolutionary biologists: what fish is the closest relative of tetrapods: the coelacanth or the equally odd-looking lobed-finned lungfish. The winner, according to analysis of the newly-published genome, is the lungfish.

"We think we have definitively shown it now," Jessica Alföldi, a research scientist at the Broad Institute of MIT and Harvard and co-first author of the paper, told NBC News. "They are very close, which is why it took so much data to figure it out."

Slow evolving genes
Scientists thought coelacanths went extinct about 70 million years ago, during the Late Cretaceous period. That changed when a fish trawler off the South African coast delivered a fresh-caught coelacanth to a local natural history museum in 1938, proving that the fish are alive and well.

The coelacanths' odd, ancient-looking looks raised eyebrows and earned it the nickname "living fossil" — much to the chagrin of evolutionary biologists, noted Alföldi. ("It makes people think there was no evolution," she explained.)

Analysis of the coelacanth genome reveals that the ancient fish is indeed evolving just about as quickly as all vertebrates in every aspect except one: its genes, the stretches of protein that code for specific functions.

Other aspects, such as the amount of transposable elements — so-called "junk DNA" — that jump around the genome, is about the same as other species, a sign of evolution. In addition, big chunks of DNA are constantly being rearranged. 

"But if we look at the proteins and say how much have these proteins changed in the last 400 million years, they have changed more in us than in the coelacanths, and they have changed a lot more in pretty much every other vertebrate species that we looked at," Alföldi said.

Why? 

One speculation is that coelacanths haven't needed to evolve, Alföldi said. They live in deep sea caves and appear to have few predators or competitors for food.

Fin to limb
Comparisons of the coelacanth genome with other vertebrates allows researchers to see what genes were lost and regulatory elements gained as lobed-finned fish crawled out of the sea and on to land. 

Some of the preliminary findings are expected, such as a suite of changes to regions of the genome that control limb development, for example. 

"This is consistent with the hypothesis that the autopod (the hand and digits) of land-living vertebrates is a modification of features already present in lobe-finned fishes, rather than something that arose entirely de novo," Matt Friedman, a paleobiologist at Oxford University, said in an email to NBC News.

Others, however, were unexpected, though "end up making total sense once you think about it," Alföldi said.

For example, genes related to smell exhibit a wide range of changes as vertebrates came on to land, which make sense given that smelling underwater is different than on land, she noted. Other changes are seen in sections of the genome that regulate immunity and the way fish and land animals poop.

For Friedman, who was not involved with the team, the findings are in line with decades of paleontological and anatomical studies of the coelacanths and other lobe-finned fish.

"Apart from specific genetic details — which are of course new — most of what is here seems to corroborate our current ideas about evolutionary changes associated with the origin of terrestriality," he said.

The specific genetic details will allow members of the research team and the broader scientific community to better understand what Yu called "the unique genomic features that shed light on the shared evolutionary past of lobe-finned fish and tetrapods."

John Roach is a contributing writer to NBC News. To learn more about him, visit his website. 

AFP / Getty Images

This picture taken on April 10, 2013 shows a newly born two-headed pig in a village in Jiujiang, east China's Jiangxi province.

On the heels of recent news about a two-headed bull shark, a two-headed pig has been born in a village in east China's Jianxi province, according to the news reports.

The photo shows a pig with two snouts, two ears and what appears to be a shared eye. A local veterinarian told the AFP news agency the animal is suffering a deformity and is unlikely to survive.

The deformity may be the same condition, called "axial bifurcation," that researchers determined was the cause of the two-headed bull shark in a study published this March in Journal of Fish Biology. 

It results from an embryo splitting into two separate organisms, or twins, but the process is incomplete.

"Halfway through the process of forming twins, the embryo stops dividing," Michael Wagner, a researcher at Michigan State University, told LiveScience. 

The mutation, he added, occurs across animals, including humans.

While rare, in addition to the pig shown here and the shark, two-headed turtles, snakes, kittens, and other critters have been reported in recent years.

John Roach is a contributing writer to NBC News. To learn more about him, visit his website. 

Argo

A system of buoys that record ocean temperatures to a depth of 6,500 feet helped scientists determine where the excess heat is stored.

The deep oceans have recently been soaking up much of the excess heat trapped under the ever-thickening blanket of greenhouse gases that humans pump into the atmosphere, according to a recent study.

The finding may help explain why the pace of global warming at the surface has slowed in recent years compared to the 1990s, a phenomenon that has left members of the climate science community scratching their heads.

"The warming at the surface hasn't stopped, but it has been less than most of the climate models have been predicting," David Pierce, a climate researcher with the Scripps Institution of Oceanography, explained to NBC News. "So the question is: Where is that extra heat going?"

Kevin Trenberth and colleagues at the National Center for Atmospheric Research reanalyzed ocean temperature records between 1958 and 2009. They found that about 30 percent of the extra heat has been absorbed by the oceans and mixed by winds and currents to a depth below about 2,300 feet.

Oceans are well-known to absorb more than 90 percent of the excess heat, but its presence in the deep ocean "is fairly new, it is not there throughout the record," Trenberth said during a teleconference with reporters on Thursday. "So the question is: What happened to produce this?"

To find out, the team used a model that accounts for variables including ocean temperature, surface evaporation, salinity, winds and currents, and tweaked the variables to determine what causes the warming at depth.

"It turns out there is a spectacular change in the surface winds which then get reflected in changing ocean currents that help to carry some of the warmer water down to this greater depth," Trenberth said. "This is especially true in the tropical Pacific Ocean and subtropics."

The change in winds and currents, he added, appears related to a pattern of climate variability called the Pacific Decadal Oscillation which in turn is related to the frequency and intensity of the El Niño/La Niña phenomenon, which impacts weather patterns around the world.

The oscillation shifted from a positive stage to a negative stage at the end of the extraordinarily large El Niño in 1997 and 1998. The negative stage of the oscillation is associated more with La Niñas, which is when the tropical Pacific Ocean is cooler and absorbs heat more readily, Trenberth explained.

"So, some of this heat may come back in the next El Niño event … but some of it is probably contributing to the warming of the overall planet, the warming of the oceans. … It means that the planet is really warming up faster than we might have otherwise expected," he said.

While this ocean mixing has been suggested by some of the models scientists use to simulate the global climate, the new study is the first to re-analyze the observational record to get at an answer, noted Pierce, who was not involved in the study.

This new work, he said, should compel the climate science community to incorporate the mixing into the full suite of models, which in turn could improve climate forecasts in the 5- to 10-year time frame most relevant to planning agencies.

"What people are getting more and more interested in is what's the actual trajectory going to be …this sort of exchange between the surface and the deep they found in this paper really affects the actual trajectory you'll see," explained Pierce.

For example, knowing when the Pacific Decadal Oscillation will switch back to the warm phase could benefit planners on the U.S. West Coast. That's because sea level rise there has been suppressed for the past two decades, Joshua Willis, a project scientist at NASA's Jet Propulsion Laboratory, noted during the teleconference.

"In California," he said, "I like to say we are running a sea level deficit of about 6 centimeters and over the next 10 or 20 years we'll probably make that up and then some."

The findings were reported online earlier this month in the journal Geophysical Research Letters. 

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. 

AP / Misha Japaridze

In this file photo, Red Square is seen as tourists walk through thick smog during a heat wave on Aug. 7, 2010. The heat wave was warmer than any since at least 1400, new research says.

The summer heat waves over the past decade that killed thousands of people in Europe, scorched the Russian wheat crop, and sent Greenland's glaciers galloping to the sea are without parallel since at least 1400, according to a new study.

The findings are based on a statistical analysis of summer seasonal temperatures inferred from tree rings, ice cores, lake sediments, and instrumental records. They are largely consistent with other global temperature reconstructions, but put a finer point on the unusualness of the recent warmth. 

Read: Warming fastest since dawn of civilization, study shows 

"Temperatures are without precedent warmer than what we're seeing over at least a 600-year time span," Martin Tingley, a climate scientist at Harvard University in Cambridge, Mass., told NBC News.

He and colleague Peter Huybers approached the question of just how extremely warm recent years are using a type of statistical analysis that allowed them to simultaneously compare one year to many years so that they can determine with high confidence whether one year was indeed warmer than all others.

They do this by using the multiple proxies — the ice cores, lake sediments, etc. — to come up with thousands of potential estimates of past climate. This frees the researchers from relying on a single best guess of past climate with a large degree of uncertainty.

"Instead of saying men in the U.S. are on average 5 feet 11 inches with some uncertainty, we get a random sample of 1,000 people and use that to build up our statistics," Tingley explained.

The approach allowed Tingley and Huybers to conclude in a paper in Thursday's issue of the journal Nature that with a 95 percent probability the high northern latitude summers of 2005, 2007, 2010 and 2011 "were warmer than all prior years back to 1400."

In addition, the pair adds that, with a 99 percent probability, "the summer of 2010 was the warmest in the previous 600 years in western Russia and (with a 90 percent probability) the warmest in western Greenland and the Canadian Arctic as well."

See slide show: Fires rage across Russia

While the findings are generally consistent with previous work, the new paper puts these extreme warm years in a spatial and temporal context, noted Shaun Marcott, a climate scientist at Oregon State University, who was not involved with the new work.

"In other words, they have provided a spatial fingerprint of where the events were extreme and to what level they were extreme over the past 600 years," he told NBC News in an email.

The cause of this unprecedented warmth, Tingley and Huybers found, is due a rise in mean global temperature, not an increase in variability. In other words, the weather is as variable as ever, but that variability now bounces around a warmer mean temperature so that temperature spikes are off the charts.

This point is important, noted Marcott, since other researchers have "argued that the frequency of warm events in the last decade occurred because of increased temperature variability. But this work here would indicate that the mean climate temperature has changed, thus explaining these more frequent extreme events."

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. 

Thomas Cameron

Wild soil mites that were captured and put in a research lab adapted to their new environment within five generations, a new study shows.

Critters can evolve over just a handful of generations to survive whatever environmental maladies humans toss their way, from climate change to over fishing, suggests a new study. 

"That is the first take-home message, and it is a positive message," Thomas Cameron, a biologist at Umea University in Sweden, told NBC News as he explained his new findings reported Tuesday in the journal Ecology Letters.

The findings overturn the common assumption that evolution only occurs gradually over hundreds or thousands of years, he said. Rather, it happens quickly and is intertwined with ecological change.

The research was based on the speed wild-caught soil mites adapted to a life of poking and prodding in a research lab. Within five generations, the wild mites genetically evolved their life-history traits to reverse a downward spiral toward extinction.

They did this by doubling the amount of time they spent as juveniles. That is, they delayed entry to adulthood.

"Those mites with the genes selecting for the slowest growth had the highest fecundity and so we see that, in the long term, the reason that the population recovered was that there was selection for increased fecundity, increased number of offspring per individual," Cameron said.

More offspring translates to a bigger population.

The delayed maturity adaptation held in populations of mites that had either 40 percent of their juveniles or adults harvested once a week, though the harvested populations changed in other ways as well. 

For example, in the case of the adult-harvested mites, the populations delayed maturity even longer, since adulthood was akin to a death sentence. And when they reached adulthood, they were bigger than the non-harvested populations and thus able to lay even more eggs.

Mites are commonly used to study broad biological questions and the findings from the lab have implications for the management of animal populations that humans hunt and fish, noted Cameron. For example, management plans may need to take rapid evolution into account, and even nudge it along.

Instead of natural selection, think of it as managed selection. In the case of land animals such white-tailed deer, game wardens could select which animals are harvested in order to nudge deer evolution itself in one direction or another. With fish, where population loss has raised concern around the world, such management may not be possible, however.

"It is certainly not very easy for fisheries to harvest small individuals but leave the big ones," Cameron noted, in one hypothetical scenario for increasing the size of fish in a population. "That's because it's not the way the nets work."

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. 

Reuters file

A woman walks her dog in Minneapolis. Indoor energy demands in the chilly city are higher than cooling demands in Miami, according to a new study.

When it's hot outside, people crank up air conditioners that usually suck electricity from coal- and natural gas-fired power plants at the root of human-caused global warming. This seems like a recipe for disaster, but it's more sustainable than living in a cold climate and cranking up the heat, a new paper suggests.

"The traditional view that living in hot desert areas is not sustainable should be re-examined," Michael Sivak, a research professor at the University of Michigan, Ann Arbor, told NBC News. "Because my data suggest that from this point of view — mainly a climate control point of view — living in very cold areas is less sustainable than hot areas."

He compared the energy demands for indoor heating and cooling in Minneapolis, Minn., the coldest metropolitan area in the country, with those in Miami, Fla., the warmest big city. He found the demands are 3.5 times greater in Minnesota.

The biggest factor in his comparison is the number of heating or cooling days per year, which reflects the demand for energy needed to heat or cool a building. The measure is calculated by comparing the mean daily outdoor temperature with 18 degrees Celsius (64.4 degree Fahrenheit). So, for example, a 10 degree Celsius day corresponds to 8 heating degree days. A 25 degree Celsius day corresponds to 7 cooling degree days. In earlier research, Sivak found that Minneapolis has 4,376 heating degree days and Miami has 2,423 cooling degree days per year.

"The need for heating in Minneapolis is more energy demanding than cooling in Miami because the difference of the ambient temperature from the desired temperature is greater in Minneapolis than in Miami," Sivak explained.

His comparison also included:

• the efficiencies of heating and cooling appliances (a typical air conditioner is about four times more energy efficient than a typical furnace or boiler primarily because it takes more energy to heat up a room than it does to cool it); 
• and the efficiencies of power plants, which generate nearly all the electricity used in cooling and 7 percent for heating. ("In terms of power plant efficiencies, cooling is worse than heating," he noted). 

When all three parameters are taken into consideration, including cooling days in Minnesota and heating days in Miami, Sivak found that Minneapolis is 3.5 times as energy-demanding as Miami.

The study doesn't examine what happens as the planet warms, and thus fewer heating days are needed in places such as Minnesota, Buffalo, N.Y., and Portland, Ore., and more cooling days are required in Miami, Phoenix and Las Vegas, but the finding may be a silver lining of global warming.

"Proportionately, you would be shifting the needs," Sivak said. "You would be heating less and you would be cooling more."

In fact, he noted in a paper published Wednesday in Environmental Research Letters, the impact of warm-city living may be even more pronounced than suggested by his calculations since "people are generally more tolerant of heat than of cold."

In other words, people are more likely to turn on their heater when there's a nip in the air than they are their AC when the temperatures begin to rise.

While all of this sounds reasonable, "you run up against basic physical constraints in a hot place that you don't in a cold place," Austin Troy, director of the transportation research center at the University of Vermont, told NBC News. Troy is also the author of The Very Hungry City, a book that illustrates the energy demands of living in warm climates.

For example, in a cold place you can build an passive solar house that uses very little energy to heat it, but similar options are lacking for people living in hot climates. And as the climate warms, in the "sun belt there'll be significantly increased cooling demands for the summer," he added.

John Roach is a contributing writer for NBC News. To learn more about him, visit his website.