December 9, 2013
As much of the United States shivers through a cold spell, readers may be hard pressed to remember the summer heat waves that have been coming in increasing frequency. The southwestern U.S. baked during this past summer. High heat in the Midwest and East Coast in summer 2012 killed 82 people, which followed a record summer in 2011. And that came after a 2010 summer that saw high heat across the Northern Hemisphere, from Asia to Europe to North America.
These events are not random and can be blamed on the disappearance of sea ice from the Arctic Ocean and, to a lesser extent, the melting of snow cover in the Arctic, say climate scientists from the Chinese Academy of Sciences in Beijing and Rutgers University. Their study was published December 7 in Nature Climate Change.
The ice that blankets the Arctic Ocean increases in winter and shrinks in extent in the summer. Likewise, Arctic lands become covered in snow in winter, and that snow melts in warmer months. This cycle is natural, but it’s been changing in recent years. The summer ice has been shrinking more, and the winter snow has been melting more. The region is warming more quickly than the rest of the world, and it’s having a variety of consequences, from alterations to the food web to a melting of permafrost to the opening up of shipping channels.
But climate scientists are also trying to figure out if the loss of snow and ice might be having larger effects on Earth’s weather patterns. Snow and ice act like mirrors, reflecting some of the Sun’s energy back out into space. When that mirror shrinks, the darker land and ocean can suck up more heat, which not only leads to more melting and a warmer Arctic but may also alter weather far away.
Arctic sea ice reaches its smallest extent in September, and that area has declined by about 8 percent every 10 years since the 1980s. Arctic snow cover, which reaches its minimum in June, has been shrinking even faster, declining about 18 percent every decade since 1979. In the new study, the researchers linked this data, as gathered from satellite observations, with atmospheric data and found that shrinking sea ice was associated with the jet stream moving northward. Snow cover also played a role but a smaller one, even though it is disappearing faster than the sea ice.
The jet stream is a ribbon of air that flows around the Northern Hemisphere from west to east and separates cold Arctic air from warmer air masses to the south. A jet stream stuck farther in the north helps to keep unbroken the warm weather patterns to the south, “increasing the probability of extreme weather events such as heat waves and droughts,” the researchers write, particularly in the eastern half of North America, eastern Europe and eastern Asia.
This study “provides further evidence linking snow and ice loss in the Arctic with summer extreme weather in mid-latitudes,” the researchers write. “As greenhouse gases continue to accumulate in the atmosphere and all forms of Arctic ice continue to disappear, we expect to see further increases in summer heat extremes in the major population centres across much of North America and Eurasia where billions of people will be affected.”
Though a heat wave may sound like a good thing right now, as many of us look out through frost-covered windows onto snowy streets, these are expensive, deadly events that kill more people than cold, cause droughts and contribute to devastating wildfires.
But the link between changes in the Arctic and heat waves in the populous mid-latitudes isn’t certain. The study showed an association, but climate scientists have yet to figure out the mechanism that might provide the link and most remain skeptical that such a link exists. “I would have more confidence in the linkage being ‘real’ if there was a well-understood and proven mechanism to support the correlations,” James Screen, a climate researcher at the University of Exeter in England, told Climate Central. And there is evidence that Arctic melting can also be associated with extremes in winter cold.
Though climate scientists have yet to understand exactly how the changes in the Arctic may be influencing weather elsewhere in the world, there is enough evidence to convince them that they should keep investigating, climate scientist James Overland of the NOAA/Pacific Marine Environmental Laboratory in Seattle, writes in an accompanying News & Views article. “The potential for an Arctic influence remains high given the outlook for further declines in summer sea-ice and snow cover over the next few decades and Arctic amplification of global temperatures.”
October 23, 2013
We tend to think of giraffes as a single species, but in Kenya not one but three types of giraffe occupy the same scruffy grasslands. These three species–the Masai, Reticulated and Rothschild’s giraffe–often encounter one another in the wild and look similar, but they each maintain a unique genetic makeup and do not interbreed. And yet, throw a male Masai and a female Rothschild’s giraffe, a male Rothschild or a female Reticulated–or any combination thereof–together in a zoo enclosure, and those different species will happily devote themselves to making hybrid giraffe babies.
What is it, then, that keeps these species apart in the wild?
Researchers from the University of California, Los Angeles, may be close to an answer. In nature, at least one of four potential barriers typically keeps similar-looking and similar-acting but distinct species from becoming intimate: distance, physical blocks, disparate habitats or seasonal differences, like rainfall. In the case of the Kenyan giraffes, the researchers could simply look at the habitat and know that physical barriers could probably be ruled out; no mountains, canyons or great bodies of water prevent the giraffes from finding one another. Likewise, giraffes sometimes have home ranges of up to 380 square miles, and those ranges may overlap. Distance alone, therefore, was probably not stopping the animals from meeting.
Either habitat or seasonal differences, they suspected, was the likely firewall preventing species from getting up close and personal with one another. To tease out the roles of these potential drivers, the authors built computer models that took into account a range of factors, including climate, habitat, human presence and genotypes from 429 giraffes that they sampled from 51 sites around Kenya. Just to make sure they weren’t unfairly excluding distance and physical obstacles from the list of possible dividers, they also included elevation values–some giraffes were found in the steep Rift Valley–and the distance between populations of giraffes sampled.
According to their statistical model, regional differences in rain–and the subsequent greening of the plains that it triggers–best explain genetic divergence between giraffe species, the researchers write in the journal PLoS One. East Africa experiences three different regional peaks in rain per year–April and May, July and August and December through March–and those distinct weather envelopes trisect Kenya.
So, although the trio of giraffe species sometimes overlap in range, the authors samples as well as previous studies revealed that they tend to each live and mate in one of those three geographic rain pockets, both within Kenya and throughout the greater East Africa region.
Giraffe species sync their pregnancies up with rain patterns to ensure enough vegetation is around to support the energetically taxing processes of gestation, birth and lactation for mother giraffes, the authors think. Not much information is available on giraffe births, but the few observations on this topic do confirm that giraffe species tend to have their babies during the local wet season, they report.
And while the models indicate that rain is the primary divider keeping giraffes apart, the authors point out that the animals also may be recognizing differences in one another’s coat patterns, for example. But scientists do not know enough about how giraffes chose mates or whether they can distinguish potential mates between species to give the species possible due credit for recognizing one another.
Whether rain alone or some combination of rain and recognition trigger mating, in the wild, at least, those mechanisms seem to work well for keeping giraffe species apart. It will be interesting to see whether this separation is maintained as climate changes.
October 3, 2013
For some humans, storms–with their raging winds and rains, passionate bursts of lightening and bone-rattling thunder–are prompts for romantic snuggling up. Likewise, few can argue that kissing in the pouring rain, Hollywood-style, isn’t a pretty thrilling experience. Insects, however, beg to differ. For them, overcast skies are the ultimate sexual buzz kill.
To assess how big of a turn-off rain is for insects, a team of Brazilian and Canadian researchers gathered together collections of three versatile arthropods: curcurbit beetles, true armyworm moths and potato aphids. Insects, they knew, possess hairs and waxy coatings to help repel water, and some, like mosquitoes, are known to have no problem flying through raindrops. On the other hand, too much heavy rain and wind can kill the little guys. So when it came to the question of how their tiny research subjects would handle sex in a storm, the team wasn’t sure what to expect.
Storms form when different air pressures collide, and the researchers decided to use decreasing air pressure as a proxy for impending rain. The team wanted to examine changes in any insect mating behaviors, including courtship and the deed itself, so they performed a number of experiments, which they describe in a paper published in PLoS One.
First, they exposed around 70 male curcurbit beetles to virgin female sex pheromones–chemical odors that normally would drive the males into a frenzy of desire–while subjecting the bugs to different barometric pressures, including stable, increasing (usually associated with clear weather but strong winds) and decreasing atmospheric pressures. Under stable or increasing pressure, they found, the male beetles eagerly scuttled into the section of their container where the pheromone was concentrated. But when the pressure was decreasing, the males were significantly less enthusiastic about initiating a meeting with a potential blushing beetle bride. In fact, they usually ignored the cues.
Next, around 70 virgin armyworm moth females were plopped into a similar experimental setting. The moths were on the cusp of peak mating season, during which females “call” to males by releasing potent cocktails of sex pheromones. When the pressure dropped, the females apparently did not feel frisky, releasing significantly less of the come-hither concoctions than under the environment of stable or increasing pressure. In nature, the researchers point out, females usually chose a nice spot high on an extended leaf to do this–in other words, the spot most likely to be splattered with rain and result in their getting washed away.
The researchers then took the obvious next step, putting both beetle and moth males and virgin females together. The male moths seemed totally turned off by both the decreasing and increasing pressure, mating fewer times under those conditions than in the stable control group.
The male beetles behaved a bit more curiously, however. When pressure was normal or increasing, the male beetles took their time setting the mood and impressing their lucky ladies by intertwining their antenna and performing other sexy pre-copulation behaviors.
When the pressure was decreasing, however, the males were all business. They skipped courtship entirely, jumped on the females and quickly got things over and done with. The researchers found this to be a bit puzzling since the males did not respond to the female hormones under decreasing pressures, but did go ahead and initiate a quickie when females were standing right next to them. This rushed copulation could be because of a “perceived reduction in life expectancy”–in other words, an it’s-the-end-of-the-world-so-let’s-do-it mentality–although that would require further investigation, they say.
Finally, the potato aphids were subjected to similar experiments. The researchers observed that females raised their backsides and hind legs into the air (the aphid’s version of a “come and get it” calling) less often in both increasing and decreasing pressure conditions. Like the moths, the team points out, the females chose the edge of a leaf to perform this booty call, so any hint of wind could potentially spell disaster for them. As for the males, not surprisingly, they, too, had no success in mating under neither the increasing or decreasing pressure conditions, perhaps because they agree that literally getting blown away during copulation is not the way to go.
The evidence, the team writes, was pretty conclusive: insects are not turned on by storms. This applies to all facets of mating, including an aversion to seeking, encouraging or initiating sex when there’s even a chance that precipitation and wind might be involved.
Although each species had their kinks–the beetles would still do it, albeit quickly, and the moths and aphids hated both increasing and decreasing pressure–the team thinks the results are general enough and cover a diverse enough spread of species to likely apply to many insects. Probably, they write, this aversion evolved as a way to avoid injury, death by drowning or being swept away by strong winds.
While the team is eager to probe even more arthropod species to confirm and better understand these behavioral patterns, they conclude that insects, at least, seem unwilling to die for love.
August 28, 2013
Over the past 15 years, a strange thing has happened. On one hand, carbon dioxide concentrations have kept on shooting up thanks to humans burning fossil fuels—in May, we passed 400 parts per million for the first time in human history.
On the other hand, despite certain regions experiencing drastically warmer weather, global average temperatures have stopped increasing. Climate change deniers have seized upon this fact to argue that, contrary to the conclusions reached by major science academies (PDF) around the world, greenhouse gas emissions do not cause global warming.
As it turns out, the truth is much grimmer. A pair of scientists from Scripps Institution of Oceanography have determined that the underlying process of global warming has merely been masked by natural decade-scale variations in the temperature of Pacific Ocean surface waters, related to the El Niño/La Niña cycle. Once that’s finished, our planet’s warming will march onward as usual.
Climate scientists have speculated about the possibility that ENSO (the El Niño-Southern Oscillation, the proper term for the cycle) was behind the apparent hiatus in warming for some time, but the scientists behind the new study—Yu Kosaka and Shang-Ping Xie—are the first to take a quantitative look at the role of Pacific surface temperatures in pausing global warming as a whole. Their paper, published today in Nature, uses climate models to show that the abnormally cool surface waters observed over the Pacific since 1998 can account for the lack of recent warming entirely.
Why has the Pacific been abnormally cool for the past 15 years? Naturally, as part of ENSO, a large swath of the ocean off the western coast of South America becomes notably warmer some years (called El Niño events) and cooler in others (La Niña events). Scientists still don’t fully understand why this occurs, but they do know that the warmer years are related to the formation of high air pressures over the Indian Ocean and Australia, and lower pressures over the eastern part of the Pacific.
Because winds move from areas of high pressure to low pressure, this causes the region’s normal trade winds to reverse in direction and move from west to east. As they move, they bring warm water with them, causing the El Niño events; roughly the reverse of this process happens in other years, bringing about La Niña. As it happens, colder surface temperatures in the Pacific—either official La Niña events or abnormally cool years that don’t quite qualify for that designation—have outweighed warm years since 1998.
That, say Kosaka and Xie, is the reason for the surprising lack of increase in global average temperatures. To come to this conclusion, they developed a climate model that, along with factors like the concentration of greenhouse gases over time and natural variations in the solar cycle, specifically takes the ENSO-related cycle of Pacific surface temperatures into account.
Typically, climate models mainly use radiative forcing—the difference between the amount of energy absorbed by the planet and the amount sent back out to space, which is affected by greenhouse gas emissions—as a data input, but they found that when their model did so, it predicted that global average temperatures would increase much more over the past 15 years than they actually have. However, when the abnormally-cool waters present in the eastern Pacific were taken into account, the temperatures predicted by the model matched up with observed temperatures nicely.
In models, the presence of these cooler waters over a huge area (a region within the Pacific that makes up about 8.2% of the Earth’s surface) serves to absorb heat from the atmosphere and thus slow down the underlying warming process. If the phenomenon is representative of reality, the team’s calculations show that it has caused the planet’s overall average temperature to dip by about 0.27°F over the past decade, combating the effects of rising carbon dioxide emissions and causing the apparent pause in warming.
This isn’t the first localized climate-related event to have effects on the progression of climate change as a whole. Last week, other researchers determined that in 2010 and 2011, massive floods in Australia slowed down the global rise in sea level that would have been been expected from observed rates of glacier melting and the thermal expansion of sea water. In many cases, it seems, the subtle and complex dynamics of the planet’s climate systems can camouflage the background trend of warming, caused by human activity.
But that trend is continuing regardless, and so the most obvious impact of this new finding is a disconcerting one: the Pacific will eventually return to normal temperatures, and as a result, global warming will continue. The scientists don’t know exactly when this will happen, but records indicate that the Pacific goes through this longer-term cycle every decade or so, meaning that the era of an abnormally-cool Pacific will probably soon be over.
Perhaps most distressing, the study implies that the extreme warming experienced in recent years in some areas—including much of the U.S.—is actually less warming than would be expected given the amount of carbon dioxide we’ve released. Other regions that haven’t seen much warming yet, meanwhile, are likely in line for some higher temperatures soon.
August 1, 2013
Climate change isn’t just affecting the natural world. Researchers have long understood that rising levels of greenhouse gas emissions will also have cascading ramifications on the dynamics of human society, whether by forcing refugees to flee from newly flood-prone areas or arid regions, by causing spikes in the prices of food crops, or by reducing the productivity of livelihoods based on fishing or grazing in certain regions.
Recently, studies and journalistic investigations have focused on one particularly chilling potential social consequence of climate change: an increased frequency of armed conflicts around the world. By studying the link between various climactic factors and rates of historical violence, researchers have speculated that the climate trends we’ll experience over the next century—hotter overall temperatures, more erratic rainfall patterns and a rising sea level—could make conflict and war more common in the future.
Now, in the most comprehensive analysis of the work on climate change and armed conflict to date, a team from UC Berkeley and elsewhere has found that these climate trends are indeed likely to significantly increase the incidence of armed conflict overall. Their paper, published today in Science, examined 60 studies to aggregate sets of data on events spanning 8000 B.C.E. to the present that examined climate variables and incidences of violence in all major regions of the globe. For example, one of the source papers focused on temperature changes and violent crime in the U.S. from 1952 to 2009, while another looked at the number of conflicts in Europe per decade from 1400 to 1999 as a function of precipitation.
Cross-comparing these studies with the same statistical methods revealed patterns that, when projected into future, suggest that by 2050 we could see 50 percent more instances of mass conflict due to the effects of climate change.
The team, led by Solomon Hsiang, specifically looked the historical relationship between climatic factors (temperature and rainfall fluctuations) and the incidence of all sorts of conflicts detailed in their source studies, which they grouped into the categories of personal crime (murder, domestic violence, rape and assault), intergroup violence (civil wars, ethnic violence and riots) and institutional breakdowns (collapses of governing bodies or even of entire civilizations such as the Mayan empire). They examined this relationship on a variety of spatial scales, ranging from countries to regions to even warmer areas within a large building or stadium, and on varying time scales, from months to years to centuries in duration.
To standardize data from many different climates and regions, the researchers calculated the number of standard deviations away from baseline averages that temperatures and rainfall rates shifted in the areas studied by the previous papers, based on the time periods covered. A standard deviation is a statistical tool used to examine how data is clustered about an average—the more standard deviations away from the average you go, the more the observation in question is an outlier.
They found that when temperatures or precipitation patterns in an area strayed from the norm, all three types of violence tended to increase, with intergroup conflict in particular surging the most during hotter periods. Specifically, a region that experienced a period of warming that fell beyond one standard deviation of average conditions saw 4 percent more personal crime and 14 percent more intergroup conflict over the period studied. In other words, assuming the variables fall in a bell curve around from average conditions, life became more violent for the roughly 32 percent of regions that significantly deviated away from average temperatures and precipitation rates.
This level of deviation, to put it into perspective, is equivalent to a country in Africa going through an entire year of temperatures averaging 0.6°F warmer than usual or to a county in the U.S. experiencing average temperatures of 5°F warmer than normal in a given month. “These are moderate changes, but they have a sizable impact on societies,” explained Marshall Burke, the study’s co-lead author and a doctoral candidate at Berkeley’s Department of Agricultural and Resource Economics.
Extrapolating to the future, these rates mean that if the entire planet went through an average of 3.6°F of warming by 2050—an optimistic limit set at the 2009 Copenhagen conference—we’d see personal crime rise by 16 percent and intergroup conflicts surge by 50 percent. The distribution of violence wouldn’t be equal, either, as climate models indicate that some areas will be hit with warming periods that fall outside two, three or even four standard deviations of the norm (and thus experience more conflict), as shown in the map below:
But what characteristics of these climate changes—heat and erratic rainfall—cause people or institutions to become violent? The mechanisms that link climate trends with violence are varied and, in many cases, unclear.
Statistics show that in cities, hotter temperatures lead to more arrests for violent crimes, and some researchers believe our basic physiological stress response to heat is to blame someone or something for the heat—but it’s unclear whether the data represent causation or correlation. On a broader level, it’s believed that reductions in agricultural productivity—especially in largely agrarian societies—can drive intergroup conflict, as can extreme weather events and reductions in resources such as potable water (due to erratic rainfall) and arable land (due to sea level rise). All of these factors are likely to come into play as the climate changes.
Of course, there are a few caveats to the finding. For one, the researchers are extrapolating from historical data, so it’s possible that even though humans have previously become more violent as temperatures increased, we could behave differently in the future. Additionally, these hypotheses can’t be rigorously tested in a lab, so it’s impossible to entirely rule out all confounding factors and establish that the climate trends cause more conflict, rather than coincidentally occurring at the same time.
The researchers, though, say that they conducted the most rigorous analysis possible. The fact that the climate-violence relationship was consistently found among a wide range of time periods, cultures and regions, they argue, indicates that there is a substantial link between the two.
If warmer temperatures and erratic precipitation really do drive violence, what can we do? The researchers say that we need to engage in research to better understand the mechanisms by which this occurs—so that eventually, just as we’ll build infrastructure to anticipate and defend against the brunt of climate change’s most dire effects, we can also create innovative social institutions and policies that might minimize violence in a warming world.