On the Cusp of Climate Change (New York Times)

U.S. Fish and Wildlife Service, via Associated Press


Sea ice is critical for all parts of the walrus’s life cycle. Adults dive and eat on these frigid platforms, and females give birth and raise their pups there. But as sea ice retreats during Arctic summers, walruses are being driven ashore.

“In the summer we’ve seen the sea ice recede far to the north,” said Chadwick V. Jay, a research ecologist for the United States Geological Survey. That change is “making it very difficult for walruses to make a living.”

In five of the last seven summers, tens of thousands of female Pacific walruses and their pups have come ashore in Alaska, farther from their preferred prey: the clam, worm and snail beds in the deep waters of the Bering and Chukchi Seas.

An Animal Gamble in the Arctic (8:59) – The Arctic is changing — fast. Two experts who have spent decades working there believe that the marine mammals who call the high latitudes home are now locked into a human-forced ecological game of chance.

Sheng Li/Reuters


In China, the tea harvest depends on the monsoons: The best tea is harvested in springtime, when the weather is still dry. But climate change threatens to extend the monsoon season.

“Post monsoon season, farmers get much less from their harvest, and a lot of the chemicals that give tea its flavor drop,” said Colin M. Orians, a chemical ecologist at Tufts University. “If climate changes the onset of the monsoon season, farmers will have a shorter window in which to harvest their tea.”

Over the next four years, Dr. Orians and his team will investigate the effects of changing temperatures and rainfall on tea quality and on the livelihoods of farmers who depend on the harvest.

Todd W. Pierson/University of Georgia


Salamanders in the Appalachian Mountains are getting smaller, and species at lower altitudes, where the greatest drying and warming has occurred, are the most affected. One species became 18 percent smaller over 55 years.

“It could be that a change in body size is the first response to climate change,” said Karen Lips, an ecologist at the University of Maryland. “Their food may be affected, and they may be producing smaller babies.”

Dr. Lips partially relied on the data of Richard Highton, a retired ecologist from the University of Maryland who spent 50 years studying and collecting salamanders that are now preserved at the Smithsonian Institution. At the time of his retirement, he noted that salamanders were mysteriously disappearing.

“If they are not nearly as big, they may not be producing as many offspring,” Dr. Lips said.

To test the theory, Dr. Lips and her team plan to raise salamanders in incubators that mimic different climates.

Nikola Solic/Reuters


Bumblebees and other pollinators are critical to global agriculture, but recent studies suggest that up to one-quarter of Europe’s bumblebee population may die out.

Researchers say that climate change is at least partly to blame, along with disease and loss of habitat.

Scientists estimate that pollinators indirectly contribute about $30 billion a year to the European economy.  “Pollinators are essential to our population,” said Jean-Christophe Vié, deputy director of the species program at the International Union for Conservation of Nature in Switzerland.

Felix Kaestle/European Pressphoto Agency

Roe Deer

Roe deer, a small, reddish-brown species that flourishes all over Europe, give birth when new plant growth provides ample nutritious food for the mother. But flowers are blooming earlier than they used to, and the deer are missing their meals.

Researchers tracked deer births from 1985 to 2011 in the Champagne region of northeastern France, where average spring temperatures have steadily increased and flowering time is coming gradually earlier. The study is online in PLOS Biology.

The deer time their fertility by light availability, not temperature. With earlier springs, they are now giving birth too late to take advantage of the best food.

Using data on 1,095 births, the scientists calculated that the mismatch between flowering time and birth over the period had grown by 36 days.

The researchers estimate that deer fitness declined by 6 percent over the period, and by 14 percent in 2007 and 2011, when flowering was particularly early.

“Roe deer are very dependent on large quantities of high quality food, and the critical stage is the first week’s supply,” said the lead author, Jean-Michel Gaillard, a director of research at the National Center for Scientific Research at the University of Lyon. “Unlike birds, for example, that can migrate and breed earlier, roe deer cannot.”

Marcelo Del Pozo/Reuters


In the Mediterranean Basin, small olive farms can support entire families. Olive trees are notoriously drought-resistant, and even in arid ecosystems they attract migratory birds and a host of insect species.

But as the region warms, some olive trees will not be as productive.

“In the south, you’re going to see a lower crop yield,” said Andrew Paul Gutierrez, an ecologist at the University of California, Berkeley. “In marginal areas, the farmers will just go out of business.”

Dr. Gutierrez and his colleagues predict that some local farmers ultimately will have to abandon their orchards, leaving barren swaths of desert where biodiversity once flourished.

Tom McHugh/Science Source


Contrary to myth, lemmings do not commit mass suicide. But populations do rise and fall in predictable cycles, to the benefit and detriment of predators like arctic foxes and migratory birds.

Recently, scientists noticed that some groups of lemmings have died off.

“The lemming cycle is the heartbeat of the terrestrial Arctic,” said Nicolas Lecomte, a biologist at the University of Moncton in Canada. “Now we’re seeing the collapse of the main prey of many terrestrial predators.”

Lemmings survive harsh winters by hiding in the snow. When warmer temperatures bring off-season rain, that snow turns to ice, and the lemmings cannot burrow.

Dr. Lecomte has found that as lemmings die off en masse, the fragile Arctic ecosystem is growing weaker.

Asit Kumar/Agence France-Presse – Getty Images

Wheat, Rice and Corn

If wheat, rice and corn are going to continue to feed the world, the crops will have to adapt to warmer temperatures. The latest report from the Intergovernmental Panel on Climate Change offers some predictions.

The analysis, published last spring in Nature Climate Change, concluded that a 3.6 degree Fahrenheit increase in temperature will bring a significant decline in crop yields.

Most projections see a decrease from 2030 onward, with greater decreases in the 2040s and 2050s.

Selective breeding and changes in irrigation methods, pest control, fertilization and planting dates may compensate, partially, for the temperature change. But most of these adaptations will work better in temperate regions, while tropical crop yields will continue to decline.

Extreme weather events — another consequence of climate change — will affect yields year-to-year in ways that are difficult to forecast.

“There are two pieces of bad news here,” said the lead author of the I.P.C.C report, Andy J. Challinor, a professor of climate impact at the University of Leeds in England. “One is that average yields are going down. The other is that yields in any given year will be less reliable.”

Patrick Kerwin


Sharks pursue their prey partly by odor, but rising carbon dioxide levels may severely impair their sense of smell.

Scientists used the smooth dogfish, a small shark, as an experimental animal. They created tanks in which some jets of water held the odor of squid, a favorite food, or no odor at all. The water in the tanks also contained varying levels of carbon dioxide.

With carbon dioxide levels resembling today’s, the sharks spent 60 percent of their time nosing about the plume with the squid odor. But in water with carbon dioxide concentrations predicted for the year 2100, the animals actively avoided the jet with the food odor, spending only 15 percent of their time there.

Any change in shark feeding habits might affect other species as well.

“There might be a decrease in hunting behavior among sharks, and an increase in prey animals as a result,” said a co-author, Ashley R. Jennings, a researcher at Boston University. “That’s assuming the prey animals aren’t being affected by CO₂ as well.”

Sue-Ann Watson

Conch Snails

As the oceans gather carbon, a small sea snail that lives in the Great Barrier Reef risks losing its famous ability to leap.

The conch snail jumps to escape from a predator, also a sea snail, that tries to inject it with a poisonous dart.

In laboratory experiments in water with increased carbon dioxide levels, the snails were 50 percent less likely to jump. And snails that did jump took nearly twice as long to do so.

The carbon dioxide and acidity disrupt a neurotransmitter receptor in the snail’s nervous system, one that other marine animals also rely on.

“They are very widespread,” said Sue-Ann Watson, a biologist at James Cook University in Australia. “It could affect many marine animals and their behaviors.”

Oceans today are 30 percent more acidic than they were 250 years ago, when the Industrial Revolution started. And it is getting worse.

“By the end of the century, if we carry on with business as usual, they will be 150 percent more acidic than they were 250 years ago,” Dr. Watson said.

Gifford Miller


As Arctic temperatures rise every summer, some of the ice on Canada’s Baffin Island melts, revealing the moss trapped underneath. Now, using radiocarbon dating, researchers have determined that until recently some of that moss hadn’t seen daylight in 44,000 years.

The melting ice not only gives scientists the chance to study ancient moss, but adds to evidence that climate change is caused by human activities, not Earth’s natural warming and cooling cycle, said Gifford H. Miller, a geologist at the University of Colorado.

“Cyclical warming is mostly related to the Earth’s irregular orbit around the sun,” he said. The Earth warms when it’s nearer the sun and cools when it’s farther away.

“For the past 10,000 years, we’ve been getting farther away,” he said. The exposure of such ancient moss suggests “the Arctic is now experiencing warmer summers than at any time since the end of the Ice Age.”

Science/Associated Press


Black-capped chickadees are commonly found in the Northeastern United States. Carolina chickadees make their home in the Southeast. Between them is a narrow zone in which both breeds reproduce in the spring.

As winter temperatures have risen over the past decade, the birds’ social scene has moved steadily northward. Today, it is about seven miles farther north than it was in 2004.

The reason? Carolina chickadees are trying to move north — like many other species dealing with climate change — and are running into the black-caps.

“As they start interacting with the black-caps, they try to hybridize,” said Robert L. Curry, a biologist at Villanova University who has studied the birds. But a high percentage of the hybrid eggs don’t hatch, he has found, and hybrid chickadees are probably less fertile.

This is unfortunate for both species in the short term, but it would be even worse for two species not accustomed to mixing.

“This is a model for what could happen if you had an introduced species moving into a new area because of climate change, then come in contact with a species it’s never met before,” Dr. Curry said.

David Inouye


To everything there is a season — including, of course, the flowering of plants. But a warming climate is changing the timing in complicated ways.

Scientists reviewed 39 years of records of flowering plants in the Rocky Mountains in Colorado, a period in which each decade saw a 0.72 degree Fahrenheit increase in average summer temperatures and a 3.5-day earlier spring snow melt.

The resulting study, published in Proceedings of the National Academy of Sciences last spring, found considerable variation in the changes in flowering, and a much larger number of species affected than previously believed.

Some form of flowering change occurred in 41 of 60 species examined. On average, first flowering advanced by 3.3 days per decade, peak flowering by 2.5 days, and final flowering by 1.5 days.

“The changes in the flower community are potentially reshuffling what’s available for the pollinators,” said a co-author, Amy M. Iler, a postdoctoral researcher at the Rocky Mountain Biological Laboratory. “We don’t know what all the consequences will be. It’s likely it will be good for some and bad for others.”

Dr. Andrew Weeks

Fruit Flies

As temperatures rise, insect populations may relocate around the globe in search of more hospitable environments. But it is the extreme highs, not just the average rise in temperatures, that may determine where they end up.

Scientists studied 10 different fruit fly species in Australia (both temperate and tropical), noting the temperature ranges each preferred for mating and everyday life, and their thresholds for extreme hot and cold.

All the species lived in environments where temperatures were sometimes less than optimal, the researchers found, but none chose places that forced them to endure extreme heat.

“Many species might undergo seasons where conditions are not optimal for growth and reproduction,” said Johannes Overgaard, a biologist at Aarhus University in Denmark and an author of the study. “They just survive the season. But what they can’t survive is temperatures beyond their threshold.”

This is bad news for the insects in Australia, who might find themselves with fewer habitable lands as extreme conditions dominate the continent. Whether this will also hold true for other continents is not yet known, Dr. Overgaard said.

Kelly Shimoda for The New York Times

Rock Snot

An unsightly algae known as “rock snot” has been surfacing in lake waters in Eastern Canada.

“It looks like torn-up toilet paper that is attached to rocks,” said John Smol, a biologist at Queen’s University in Ontario who is studying the algae’s growth. “It’s an aesthetic issue, and as it decomposes it becomes a smell issue.”

Rock snot, or didymo, was thought of as an invasive species introduced by humans. But an analysis of fossilized algae in the lakes indicates that it is native.

The algae was present in one lake in Quebec since at least 1970, 36 years before it was first noticed, Dr. Smol’s team found.

Didymo tends to grow in flowing waters. Warmer winters may be producing less ice and snow that disrupt the flow.

Over time, the rock snot will become much more than an eyesore, Dr. Smol said. It will displace other organisms and destroy fish habitats.

F. Stuart Westmorland/Science Source

Coral Reefs

Ocean acidification endangers coral in every ocean. But researchers haverecently discovered unusual reefs in Palau that are thriving in increasingly acidicified waters.

Ocean acidification occurs when carbon emitted by human activities mixeswith ocean waters. This decreases carbonate ions in the water, which coral andother organisms need to form their protective shells.

Yet in 2012, researchers working in the waters off Palau identified coralreefs that were both extremely acidified and very healthy. What’s differentabout these reefs, said Kathryn Shamberger, anoceanographer at Texas A&M University, is that the waters became acidifiedthrough natural means.

“The growth of the reef itself and the breathing of the organisms onthe reef,” not man-made emissions, added carbon to the water, she said.

In a typical reef these products would be flushed out before they could havemuch effect. But the waters in Palau pool around its many small islands.

Might reefs suffering from man-made acidification survive as well as these?Dr. Shamberger and others are trying to figure thatout.

Eric Sanford


Increasing ocean acidity makes it difficult for marine species to build their shells and, by softening calcium carbonate, makes shells weaker. That’s bad news not only for clams, oysters and scallops, but for tens of thousands of lesser known species — echinoderms like star fish and sea urchins, colonies of tiny invertebrates, reef corals and many others.

In June, The Biological Bulletin devoted an issue to research on ocean calcification with papers and reviews on a large variety of organisms.

“Climate change and ocean acidification are going to manifest themselves in the ways species interact — eating each other, facilitating each other’s growth,” said an editor of the issue, Gretchen Hofmann, a marine biologist at the University of California, Santa Barbara.

And yet, she added, there is some hope. “In coastal areas there are plants that actually change the pH of the water — in a good way. Eel grass and surf grasses can provide refuge from future acidification.”

Sophie McCoy

Coral Algae

Coralline algae are the cement that binds many reefs together. By filling the gaps between corals with a hard outer shell, these algae fortify the reef and provide shelter for growing organisms.

To produce that shell, this special algae — much like oysters and snails — require a steady supply of carbonate. But as carbonate becomes harder and harder to come by in increasingly acid oceans, the once-dominant species of coralline algae can no longer grow shells as thick as they once were. Other species are moving in to claim more territory.

For now, it might not be so bad to give these competitors a chance, said Sophie McCoy, an ecologist with the Plymouth Marine Laboratory in England, who lead a study on the phenomenon when she was at the University of Chicago earlier this year.

“In the short term, I think it might be a good thing in terms of local biodiversity,” she said. In the long run, however, “all the species of this algae will start to be affected.”

That could mean less coral overall, and less habitat for the organisms that call it home.

Michael Francis McElroy for the New York Times

Invasive Species

Biological intruders, from California’s medflies to Florida’s Burmese pythons, cost the United States billions of dollars every year. Rising temperatures and changing weather patterns may make them even harder to control.

“Biology can be very complicated, especially when climate change comes in,” said Andrew Paul Gutierrez, an ecologist at the University of California, Berkeley. “That’s going to affect these species in unknown ways.”

In a book on the subject, Dr. Gutierrez notes one jarring possibility: that higher temperatures may invite still more invasive species into fragile ecosystems.

Jim Gathany/Center for Disease Control


Historically, the highlands of Ethiopia offered protection from deadly, mosquito-borne malaria. But perhaps not for much longer.

The disease was mitigated at higher altitudes, where cooler temperatures kept mosquitoes in check. Now, malaria is spreading into higher elevations during warmer years, then back into lower altitudes when temperatures cool.

Looking at temperature records from the two regions, there is a clear link between the changing climate and higher rates of the disease, said Mercedes Pascual, an ecologist at the University of Michigan.

“The disease is seasonal,” she said. “But climate change here could make the problem much bigger.”

She and her colleagues found that a 1.8 degree Fahrenheit temperature increase could result in an additional three million malaria cases annually in Ethiopia among those under age 15.