Glaciers are melting sea levels are rising cloud

Glaciers are melting, sea levels are rising, cloud forests are drying. It's becoming clear that humans have caused most of the past century's warming by releasing heattrapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650, 000 years. We call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. The rhythms of climate that all living things have come to rely upon are changing.

Greenhouse effect The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse. First, sunlight shines onto the Earth's surface, where it is absorbed and then radiates back into the atmosphere as heat. In the atmosphere, “greenhouse” gases trap some of this heat, and the rest escapes into space. The more greenhouse gases are in the atmosphere, the more heat gets trapped.

Levels of greenhouse gases (GHGs) have gone up and down over the Earth's history, but they have been fairly constant for the past few thousand years. Through the burning of fossil fuels and other GHG emissions, humans are enhancing the greenhouse effect and warming Earth. Scientists often use the term "climate change" instead of global warming. This is because as the Earth's average temperature climbs, winds and ocean currents move heat around the globe in ways that can cool some areas, warm others, and change the amount of rain and snow falling. As a result, the climate changes differently in different areas.

Aren't temperature changes natural? The average global temperature and concentrations of carbon dioxide (one of the major greenhouse gases) have fluctuated on a cycle of hundreds of thousands of years as the Earth's position relative to the sun has varied. As a result, ice ages have come and gone. However, for thousands of years now, emissions of GHGs to the atmosphere have been balanced out by GHGs that are naturally absorbed. As a result, GHG concentrations and temperature have been fairly stable. Occasionally, other factors briefly influence global temperatures. Volcanic eruptions, for example, emit particles that temporarily cool the Earth's surface. But these have no lasting effect beyond a few years. Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the industrial revolution. Changes this large have historically taken thousands of years, but are now happening over the course of decades.

Scientists are already seeing some of climate changes occurring more quickly than they had expected. According to the Intergovernmental Panel on Climate Change, eleven of the twelve hottest years since thermometer readings became available occurred between 1995 and 2006. What will we do to slow this warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the face of the Earth as we know it—coasts, forests, farms and snow-capped mountains— hangs in the balance.

People Health "Natural" disasters. Projected changes in temperature and precipitation under global warming are likely to lead to other effects that threaten human health and safety. For example, changing precipitation patterns and prolonged heat can create drought, which can cause forest and peat fires. However, a warming atmosphere also holds more moisture, so the chance of extreme rainfall and flooding continues to rise in some regions with rain or snow. In many heavily populated areas, sea-level rise is more likely to put people in the path of storm surges, coastal flooding, more intense tropical hurricanes and typhoons. Poor air quality. Three key ingredients—sunlight, warm air, and pollution from power plants and cars burning coal and gasoline—combine to produce ground-level ozone (smog). Higher air temperatures increase smog, if fossil fuel pollution remain the same. Allergens and other nuisances. Warmer temperatures and higher concentrations of carbon dioxide in the atmosphere stimulate some plants to produce more potent allergens. Allergy-related diseases rank among the most common and chronic illnesses. Spreading diseases. Scientists expect a warmer world to bring changes in "disease vectors"—the mechanisms that spread some diseases. Insects previously stopped by cold winters are already moving to higher latitudes (toward the poles).

Los Angeles Smog

Food Reduced yields. The productivity of crops and livestock, including milk yields, may decline because of high temperatures and drought-related stress. Increased irrigation. Regions of the world that now depend on rain-fed agriculture may require irrigation, bringing higher costs and conflict over access to water. More pests. Insect and plant pests may survive or even reproduce more often each year if cold winters no longer keep them in check. Risks to fisheries. Shifts in the abundance and types of fish and other seafood may hurt commercial fisheries, while warmer waters may pose threats to human consumption, such as increasing the risk of infectious diseases.

Water Use Humans use water for everything from drinking and bathing to growing crops, supporting livestock and fish farms, shipping goods, generating electricity. Yet climate change is producing profound changes in this precious commodity, threatening water availability, access, and even quality. Decline in drinking water—both quantity and quality—is expected for these reasons: ► The shrinking of mountain glaciers threatens drinking water supplies for millions of people. ► Sea-level rise can lead to saltwater intrusion into groundwater drinking supplies, especially in low-lying, gently sloping coastal areas. Disruptions to power supply. Lower lake and river levels may threaten the capacity of hydroelectric plants, while higher temperatures may mean that water is too warm to cool coal and nuclear power plants.

Costs Damage to property and infrastructure. Sea-level rise, floods, droughts, wildfires, and extreme storms require extensive repair of essential infrastructure such as homes, roads, bridges, railroad tracks, airport runways, power lines, dams, levees, and seawalls. Lost productivity. Disruptions in daily life related to climate change can mean lost work and school days and harm trade, transportation, agriculture, fisheries, energy production, and tourism. Mass migration and security threats. Global warming is likely to increase the number of "climate refugees"—people who are forced to leave their homes because of drought, flooding, or other climaterelated disasters.

Extreme Wet & Extreme Dry A warmer climate spurs the evaporation of water from land sea and allows the atmosphere to hold more moisture—thus setting the stage for more extreme precipitation. Wet places tend to get wetter. Atmospheric circulation over oceans, plains, and mountains helps determine where rainforests thrive and semiarid regions develop. Extreme Dry Increased drought in dry areas. In drier regions, evapotranspiration may produce periods of drought. Precipitation has declined in the tropics and subtropics since 1970. Southern Africa, the Sahel region of Africa, southern Asia, the Mediterranean, and the U. S. Southwest, for example, are getting drier. Expansion of dry areas. Scientists expect the amount of land affected by drought to grow by mid-century—and water resources in affected areas to decline as much as 30 percent.

Land Ice Shrinking land ice is wreaking havoc across the globe. Sea-level rise. Long locked away in polar regions and mountains, glaciers are adding new freshwater to the world's oceans. Long-term decline in water resources. Nearly one-sixth of the world's population lives near rivers that derive their water from glaciers and snow cover. Short-term increase in flash floods. Many rivers that derive their water from melting glaciers or snow are likely to have earlier peak runoff in spring and an overall increase in runoff, at least in the short term. Accelerated warming from albedo. Land ice in polar regions reflects some of the sun's energy back into space (known as albedo), helping keep the planet cool. As this ice shrinks and darker land is exposed, it absorbs more solar energy—creating a feedback loop that accelerates the planet's warming.

Sea Level Higher seas endanger coastal communities—where 40 percent of the world's population lives—and threaten groundwater supplies. As ocean temperatures rise, the warmer water expands. Trapped within a basin bounded by the continents, the water has nowhere to go but up. The consequences of sea level rise include: Threats to coastal communities. Some 40 percent of the world's population lives within 62 miles (100 kilometers) of the ocean, putting millions of lives and billions of dollars' worth of property and infrastructure at risk. Saltwater intrusion. Sea-level rise can mean that saltwater intrudes into groundwater drinking supplies, contaminates irrigation supplies, or overruns agricultural fields.

Sea Ice Where in the past, some Arctic sea ice grew to 3 meters thick over multiple years, now much of the ice has only one year of growth, making it much more susceptible to melting in the summer. Scientists project that the Arctic Ocean may be ice-free in summer in just a few decades. The cascade of consequences include: Accelerated warming due to higher Arctic temperatures. The loss and thinning of Arctic sea ice raises regional temperatures, delaying the formation of sea ice in the fall, and transferring more heat from the ocean to the air. If higher air temperatures speed the degradation of frozen ground (permafrost) on adjacent lands, they could release vast stores of carbon often trapped in the permafrost for thousands of years—further amplifying climate change. Severe threats to polar creatures. Polar creatures that depend on ice for all or parts of their life cycle are highly threatened by a warming world. In the Arctic, polar bears must swim greater distances in open water to find the sea-ice habitat that is home to their prey: seals, which use breathing holes through the ice. Threats to indigenous ways of life, some of which have flourished in the Arctic for thousands of years. Traditional hunting methods, for example, are becoming more risky because of thin ice.

Alaska Permafrost

Lakes & Rivers Climate change is already beginning to affect plants and animals that live in freshwater lakes and rivers, altering their habitat and bringing lifethreatening stress and disease. Displacement of cold-water species. Streams and lakes may become unsuitable for cold-water fish but support species that thrive in warmer waters. Dead zones. In a warming climate, a warmer upper layer in deep lakes slows down air exchange. This, in turn, often creates large "dead zones" —areas depleted of oxygen and unable to support life. Effects on reproduction. Earlier snowmelt, rising amounts of precipitation that falls as rain rather than snow, and more severe and frequent flooding may affect the reproduction of aquatic species. Some salmon populations have declined, for example, as more intense spring floods have washed away salmon eggs laid in stream beds.

Salmon Migration

Land Rising temperatures and shifting precipitation patterns are changing the geographic areas where mammals, birds, insects, and plants that live on land can survive—and are affecting the timing of lifecycle events, such as bud bursts, leaf drop from trees, pollination and reproduction. Forced migrations and extinctions. Plants and animals are migrating to higher altitudes and latitudes. Land-based species that already live in extreme habitats—such as plants and animals found only in alpine regions—may become extinct because they literally have no place to go. Desynchronization of life-cycle events. For example, bird migrations timed to seasonal changes or temperatures may begin earlier. Meanwhile warmer temperatures in late winter may force flowers to bud early, leaving them vulnerable to late-season frost. Changing woodlands. As conditions change, habitats become unsuitable for saplings to grow, and species attempt to migrate. Because trees are so long-lived, the effects may not be noticeable for many years. However, species that now grow only in certain areas— such as the sugar maple, now found in parts of the United States and Canada—may be quite rare in their southern range by the end of this century.

Salt Water Although marine species are more difficult to see and less well studied than land freshwater species, they are known to be experiencing some of the same—and some different—effects from global warming. Coral bleaching. As seawater temperatures rise above the range that corals can tolerate, they are expelling their symbiotic algae and exposing white skeletons—a process known as bleaching. Harm to wetlands. Coastal wetlands, salt marshes, and mangroves are highly vulnerable to inundation as sea levels rise. Freshwater from melting land ice and extreme rainfall—the results of global warming— dilutes salinity levels near shore, potentially disrupting the delicate balance among creatures in these productive waters.

Виконала студентка економічного факультету групи Екф-11 с Юрків Олена