

Early signs of global warming:
Ocean warming, sea-level rise and coastal flooding
Warmer temperatures increase melting of mountain glaciers, increase ocean heat content, and cause ocean water to expand. Largely as a result of these effects, global sea level has risen 4 to 10 inches (10-25 cm) over the past 100 years. With additional warming, sea level is projected to rise from half a foot to 3 feet (15-92 cm) more during the next 100 years. On average, 50 to 100 feet (15-30 meters) of beach are lost for every foot (0.3 meters) of sea-level rise. Local land subsidence (sinking) and/or uplift due to geologic forces and coastal development will also affect the rate of coastal land loss.
Heat waves and periods of unusually warm weatherFrequent and severe heat waves lead to increases in heat-related illness and death, especially in urban areas and among the elderly, the young, the ill, and the poor.
Glaciers melting Over the past 150 years, the majority of mountain glaciers monitored have been shrinking. Many glaciers at lower latitudes are now disappearing, and scientists predict that, under some plausible warming scenarios, the majority of glaciers will be gone by the year 2100. As glaciers continue to shrink, summer water flows will drop sharply, disrupting an important source of water for irrigation and power in many areas that rely on mountain watersheds. Arctic and Antarctic warmingParts of Canada, Alaska, Siberia, and the Antarctic have been experiencing warming well above the global average for the past few decades. This trend fits climate model predictions for a world with increasing levels of greenhouse gases. Melting permafrost is forcing the reconstruction of roads, airports, and buildings and is increasing erosion and the frequency of landslides. Reduced sea ice and ice shelves, changes in snowfall, and pest infestations have affected native plants and animals that provide food and resources to many people.
Spreading diseaseWarmer temperatures allow mosquitoes that transmit diseases such as malaria and dengue fever to extend their ranges and increase both their biting rate and their ability to infect humans.
Earlier spring arrivalSpring now arrives earlier in many parts of the world. Evidence of this comes from earlier thaw dates for rivers and lakes; earlier dates for plant blooming and leafing; and earlier animal egg-laying, spawning and migration. An earlier spring may disrupt animal migrations, alter competitive balances among species, and cause other unforeseen problems.
Plant and animal range shifts and population changesPlants and animals generally react to consistently warmer temperatures by moving to higher latitudes and elevations. Recent studies reveal that some species have already started to shift their ranges, consistent with warming trends. Many populations and species may become more vulnerable to declining numbers or extinction if warming occurs faster than they can respond or if human development presents barriers to their migration.
Coral reef bleachingReefs in 32 countries experienced dramatic bleaching in 1997-98. Bleaching results from the loss of microscopic algae that both color and nourish living corals.
Downpours, heavy snowfalls, and floodingA warmer climate will bring an increase in precipitation worldwide, especially during winter and in mid- to high latitudes, according to climate model projections. In addition, more precipitation is expected to fall in downpours and heavy snowstorms leading to increased flooding and damages. The area of the U.S. affected by extreme rainfall has increased significantly since 1910. Heavy rainfalls have also increased in Japan, the former Soviet Union, China, and Australia. As climate change increases the risk of flooding, human changes in land use and land cover can also contribute to the growing risk of flooding.
Droughts and firesAs the climate heats up, droughts are expected to become more frequent and severe in some locations. Sustained drought makes wildfires more likely, and crops and trees more vulnerable to pest infestations and disease.
