"Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.
Impacts of Global Warming
Global warming is already underway with consequences that must be faced today as well as tomorrow. Evidence of changes to the Earth's physical, chemical and biological processes is now evident on every continent.To fully appreciate the urgency of climate change, it's important to understand the ways it affects society and the natural environment. Sea levels are rising and glaciers are shrinking; record high temperatures and severe rainstorms and droughts are becoming increasingly common. Changes in temperatures and rainfall patterns alter plant and animal behavior and have significant implications for humans. In this section, explore the connections between the climate data and the changes happening around you—and those you can expect to see in the future—in all parts of the globe, including your own backyard.
Not only are global warming-induced changes currently underway, but scientists also expect additional effects on human society and natural environments around the world. Some further warming is already unavoidable due to past heat-trapping emissions; unless we aggressively reduce today's emissions, scientists project extra warming and thus additional impacts.
The Climate Hot Map arranges current and future climate impacts into five main groupings:
As our climate changes, the risk of injury, illness, and death from the resulting heat waves, wildfires, intense storms, and floods rises.
- Extreme heat. If high temperatures, especially when combined with high relative humidity, persist for several days (heat waves), and if nighttime temperatures do not drop, extreme heat can be a killer. Of all climate-related projections by scientists, rising temperatures are the most robust. Higher temperatures are also the most influenced by human behavior: the fewer heat-trapping emissions we release into the atmosphere, the cooler we can keep our planet. Because winter temperatures are rising faster than summer ones, cold-related deaths are likely to decline.
- "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, putting residents and firefighters in danger. 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 and coastal flooding. Warmer ocean waters may spawn more intense tropical hurricanes and typhoons while ocean cycles continue to be a factor in the frequency of tropical cyclones.
- 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), which humans experience as poor air quality. Higher air temperatures increase smog, if sunlight, fossil fuel pollution, and air currents remain the same.
- Allergens and other nuisances. Warmer temperatures and higher concentrations of carbon dioxide in the atmosphere stimulate some plants to grow faster, mature earlier, or produce more potent allergens. Common allergens such as ragweed seem to respond particularly well to higher concentrations of CO2, as do pesky plants such as poison ivy. Allergy-related diseases rank among the most common and chronic illnesses that can lead to lower productivity.
- 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). Warmer oceans and other surface waters may also mean severe cholera outbreaks and harmful bacteria in certain types of seafood. Still, changes in land use and the ability of public health systems to respond make projecting the risk of vector-borne disease particularly difficult.
- Climate trends differ by region. People who live in floodplains, for example, are more likely to see river or coastal flooding. Similarly, people who live in regions with poor air quality today are at greater risk from poor air quality days in the future.
- Some people are more vulnerable to illness or death. Young children, the elderly, and those who are already ill are less able to withstand high temperatures and poor air quality, for example. Temperature extremes and smog hit people with heart and respiratory diseases, including asthma, particularly hard.
- Wealthy nations are more likely to adapt to projected climate change and recover from climate-related disasters than poor countries . Even within nations, less economically fortunate individuals are more vulnerable because they are less likely to have air conditioning and well-insulated homes, and because they have fewer resources to escape danger.
Climate-related threats to global food production include risks to grain, vegetable, and fruit crops, livestock, and fisheries.
- 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.
- Planting and harvesting changes. Shifting seasonal rainfall patterns and more severe precipitation events—and related flooding—may delay planting and harvesting.
- Decreased arability. Prime growing temperatures may shift to higher latitudes, where soil and nutrients may not be as suitable for producing crops, leaving lower-latitude areas less productive.
- More pests. Insect and plant pests may survive or even reproduce more often each year if cold winters no longer keep them in check. New pests may also invade each region as temperature and humidity conditions change. Lower-latitude pests may move to higher latitudes, for example.
- 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. Extreme ocean temperatures and ocean acidification place coral reefs-—the foundations of many of the world's fisheries-—at risk.
Nations that lose arable land and critical fisheries may not have the resources or climate to pursue reasonable-cost options for maintaining food security. Some nations are also more vulnerable to unfavorable international trade agreements and regional strife that may interrupt food distribution.
Humans use water for everything from drinking and bathing to growing crops, supporting livestock and fish farms, shipping goods, generating electricity, and simply relaxing and having fun. 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:
► Municipal sewer systems may overflow during extreme rainfall events, gushing untreated sewage into drinking water supplies.
► Loss of mountain snowpack and earlier spring snowmelt spurred by higher temperatures reduce the availability of drinking water downstream.
► 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.
- Decline in irrigation supplies. Loss of mountain snowpack reduces the amount of water available for irrigation downstream, while earlier spring snowmelt affects the timing. Saltwater intrusion may contaminate the supply from groundwater.
- Higher shipping costs. Lower lake and river levels may reduce the capacity of ships to carry freight safely due to the danger of their running aground or preclude the use of large ships altogether—both of which may increase shipping costs for food and other commodities.
- 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, leading to power brownouts. Shrinking mountain glaciers threaten electricity generation as well.
- Effects on recreation. Reduced snowpack and earlier spring snowmelt put traditional winter sports, such as skiing and snowmobiling, at risk, while lower water levels in lakes and rivers increase the costs of maintaining recreational amenities such as pleasure boat docks and even beaches.