Some U.S. politicians have been attacking environmental regulations, arguing that they hurt the economy and that the costs outweigh the benefits. But four decades of data refute that claim and show we need not choose between a clean environment and economic growth.

For environmentalists protesting the Keystone XL pipeline, the battle is about more than just transporting tar sands oil from Alberta. It’s about whether the United States — and the rest of the world — will finally come to its senses about global warming.

Airborne microbes can travel thousands of miles and high into the stratosphere. Now scientists are beginning to understand the possible role of these microbes — such as bacteria, fungal spores, and tiny algae — in creating clouds, causing rain, spreading disease, and even changing climate.

From understanding the cumulative impacts of widely used chemicals to preparing for life in a warming world, a host of environmental health issues now face medical experts. In an interview with Yale Environment 360, Lynn Goldman, dean of the George Washington University School of Public Health and Health Services, talks about meeting the challenges.

For eons, the polar marine food chain has been closely linked to the seasonal formation and retreat of sea ice. Now, as that ice rapidly melts in the Arctic and along the Antarctic Peninsula, this intricate web of life is undergoing major shifts, benefiting some creatures and putting others at risk.

For millennia, the blanket of ice covering the Arctic Ocean protected the shore from damaging storms. But as that ice buffer disappears, increasingly powerful storm surges are eroding the coastline and sending walls of seawater inland, devastating Arctic ecosystems that support abundant wildlife.

Grizzly bears mating with polar bears. Red foxes out-competing Arctic foxes. Exotic diseases making their way into once-isolated polar realms. These are just some of the worrisome phenomena now occurring as Arctic temperatures soar and the Arctic Ocean, a once-impermeable barrier, melts.

William Reilly led the national commission that investigated the Deepwater Horizon oil spill and says he was struck by the totally inadequate response plans that were in place. In an interview with Yale Environment 360, he talks about why it’s crucial to carry out the reforms needed to prevent future disasters.

Doug Peacock has been tireless defender of the Yellowstone grizzly for decades, but he believes the bear may now be facing its toughest threat yet. In an interview with Yale Environment 360, Peacock talks about the insect infestation that is destroying a key food source for grizzlies and recalls some of his closest encounters with the bears.

With the Arctic Ocean heading toward a largely ice-free state in summer, scientists are looking for areas that may help preserve ice-dependent creatures. In an interview with Yale Environment 360, geologist Stephanie Pfirman talks about the need for a refuge north of Canada and Greenland that researchers say could be a kind of Noah’s Ark in the age of global warming.

The fringes of the coldest continent are starting to feel the heat, with the northern Antarctic Peninsula warming faster than virtually any place on Earth. These rapidly rising temperatures represent the first breach in the enormous frozen dome that holds 90 percent of the world’s ice.

In China, millions of tons of waste from livestock farms are causing severe water pollution and massive emissions of methane. Now, some large livestock operators are turning to biogas fuel production in hopes of creating “ecological” factory farms.

Across the Far North, populations of caribou — an indispensable source of food and clothing for indigenous people — are in steep decline. Scientists point to rising temperatures and a resource-development boom as the prime culprits.

In the early 20th century, Russian botanist Nikolai Vavilov created a preserve outside St. Petersburg that today contains one of the world’s largest collections of rare seeds and crops. Now, scientists and conservationists are waging an international campaign to save the reserve’s fields from being bulldozed for housing development.

As warming intensifies, scientists warn, the oxygen content of oceans across the planet could be more and more diminished, with serious consequences for the future of fish and other sea life.

With 20 percent of the world’s population but just 7 percent of its available freshwater, China faces serious water shortages as its economy booms and urbanization increases. The government is planning massive water diversion projects, but environmentalists say conservation — especially in the wasteful agricultural sector — is the key.

Unearthing photographs of the Himalaya dating back more than a century, mountaineer and filmmaker David Breashears has assembled a powerful visual record of the rapid retreat of the region’s glaciers. By comparing archival photographs from such renowned explorers as George Mallory to photographs taken in the past three years, Breashears has documented the steady disappearance of these great rivers of ice, whose melting will eventually threaten the water supplies of hundreds of millions of people across Asia.

The polar bear has long been a symbol of the damage wrought by global warming, but now biologist Andrew Derocher and his colleagues have calculated how long one southerly population can hold out. Their answer? No more than a few decades, as the bears’ decline closely tracks that of the Arctic’s disappearing sea ice.

The surest sign of a warming Earth is the steady melting of its ice zones, from disappearing sea ice in the Arctic to shrinking glaciers worldwide. Now, scientists are using increasingly sophisticated satellite technology to measure the extent, thickness, and height of ice, assembling an essential picture of a planet in transition.

The massive oil spill in the Gulf of Mexico is a warning, conservationists say, of what could happen in the Arctic as melting sea ice opens the Arctic Ocean to oil and gas drilling. Many experts argue that the time has come to adopt an Arctic Treaty similar to the one that has safeguarded Antarctica for half a century.

Flying dwarfs any other individual activity in terms of carbon emissions, yet more and more people are traveling by air. With no quick technological fix on the horizon, what alternatives — from high-speed trains to advanced videoconferencing — can cut back the amount we fly?