Potential Effects of Global Warming

The most obvious impact of global warming will be changes in both average and extreme temperature and precipitation, but warming will also enhance coastal erosion, lengthen the growing season, melt ice caps and glaciers, and alter the range of some infectious diseases, among other things.

For most places, global warming will result in more hot days and fewer cool days, with the greatest warming happening over land. Longer, more intense heat waves will become more frequent. High latitudes and generally wet places will tend to receive more rainfall, while tropical regions and generally dry places will probably receive less rain. Increases in rainfall will come in the form of bigger, wetter storms, rather than in the form of more rainy days. In between those larger storms will be longer periods of light or no rain, so the frequency of drought will increase. Hurricanes will likely increase in intensity due to warmer ocean surface temperatures.

Global Warming
• Introduction
• What is Global Warming?
• Evidence for Global Warming
• Building a Climate Model
• Predicting Future Warming
• Potential Effects of Global Warming
• References

It is impossible to pin any one unusual weather event on global warming, but evidence is emerging that suggests that global warming is already influencing the weather. The IPCC reports that both heat waves and intense rain events have increased in frequency during the last 50 years, and human-induced global warming more likely than not contributed to the trend. Satellite-based rainfall measurements show tropical areas got more rain in the form of large storms or light rainfall instead of moderate storms between 1979 and 2003. Since the 1970s, the area affected by drought and the number of intense tropical cyclones also have increased, trends that IPCC scientists say were more likely than not influenced by human activities, though in the case of cyclones, the record is too sparse to draw any certain conclusions.

Global warming will shift major climate patterns, possibly prolonging and intensifying the current drought in the U.S. Southwest. The white ring of bleached rock on the once-red cliffs that surround Lake Powell indicate the drop in water level over the past decade, the result of repeated winters with low snowfall. (Photograph ©2006 Tigresblanco.)

The weather isn’t the only thing global warming will impact: rising sea levels will erode coasts and cause more frequent coastal flooding. The problem is serious because as much as 10 percent of the world’s population lives in coastal areas less than 10 meters (about 30 feet) above sea level. The IPCC estimates that sea levels will rise between 0.18 and 0.59 meters (0.59 to 1.9 feet) by 2099 because of expanding sea water and melting mountain glaciers.

Apart from driving temperatures up, global warming is likely to cause bigger, more destructive storms, more widespread drought, and coastal damage from high sea levels. With some exceptions, the tropics will likely receive less rain (orange) as the planet warms, while the polar regions will receive more precipitation (green). White areas indicate that fewer than two-thirds of the climate models agreed on how precipitation will change. Stippled areas reveal where more than 90 percent of the models agreed. (©2007 IPCC WG1 AR-4.)

These estimates of sea level rise may be low, however, because they do not account for changes in the rate of melt from the world’s major ice sheets. As temperatures rise, ice will melt more quickly. New satellite measurements reveal that the Greenland and West Antarctic ice sheets are shedding about 125 billion tons of ice per year—enough to raise sea levels by 0.35 millimeters (0.01 inches) per year. If the melting were to accelerate, the rise in sea level could be significantly higher. For instance, the last time global temperatures were a degree or so warmer than today, sea levels were about 6 meters (20 feet) higher, with the water mainly coming from the melting of the Greenland and the West Antarctic ice sheets. Neither ice sheet is likely to disappear before 2100, but there is the danger that global warming could initiate massive losses from the Greenland and Antarctic ice sheets that will continue or even accelerate over future centuries.

Global warming is also putting pressure on ecosystems, the plants and animals that co-exist in a particular climate. Warmer temperatures have already shifted the growing season in many parts of the globe. Spring is coming earlier, and that means that migrating animals have to start earlier to follow food sources. And since the growing season is longer, plants need more water to keep growing or they will dry out, increasing the risk of fires. Shorter, milder winters fail to kill insects, increasing the risk that an infestation will destroy an ecosystem. As the growing season progresses, maximum daily temperatures increase, sometimes beyond the tolerance of the plant or animal. To survive the climbing temperatures, both marine and land-based plants and animals have started to migrate towards the poles. Those species that cannot migrate or adapt face extinction. The IPCC estimates that 20-30 percent of plant and animal species will be at risk of extinction if temperatures climb more than 1.5° to 2.5°C.

The people who will be hardest hit will be residents of poorer countries who do not have the resources to fend off changes in climate. As tropical temperature zones expand, the reach of some infectious diseases like malaria will change. More intense rains and hurricanes, rising sea levels, and fast-melting mountain glaciers will lead to more severe flooding. Hotter summers and more frequent fires will lead to more cases of heat stroke and deaths, and to higher levels of near-surface ozone and smoke, which would cause more ‘code red’ air quality days. Intense droughts could lead to an increase in malnutrition. On a longer time scale, fresh water will become scarcer during the summer as mountain glaciers disappear, particularly in Asia and parts of North America. On the flip side, warmer winters will lead to fewer cold-related deaths, and the longer growing season could increase food production in some temperate areas.

Sea levels crept up about 20 centimeters during the twentieth century. Most of the rise happened because water expands as it warms, though melting mountain glaciers also contributed to the change. Sea levels are predicted to go up between 0.18 and 0.59 meters over the next century, though the increase could be greater if ice sheets in Greenland and Antarctica melt more quickly than predicted. Higher sea levels will erode coastlines and cause more frequent flooding. (Graph ©2007 Robert Rohde.)

Ultimately, global warming will impact life on Earth in many ways, but the extent of the change is up to us. Scientists have shown that human emissions of greenhouse gases are pushing global temperatures up, and many aspects of climate are responding to the warming in the way that scientists predicted they would. Ecosystems across the globe are already affected and surprising changes have already taken place. Polar ice caps are melting, plants and animals are migrating, tropical rain is shifting, and droughts are becoming more widespread and frequent. Since greenhouse gases are long-lived, the planet will continue to warm and changes will continue to happen, but the degree to which global warming changes life on Earth depends on our decisions.

 References
 Predicting Future Warming

As much as 10 percent of the world’s population lives in coastal regions where the elevation is less than 10 meters above sea level. These communities will become increasingly prone to storm damage and flooding as sea levels rise. Among the most vulnerable countries is Bangladesh, which has low elevation, a high population density, and is one of the world’s poorest nations. Red areas indicate populations that live less than 10 meters above sea level, while green areas show the population density in areas with an elevation greater than 10 meters. (Image courtesy Socioeconomic Data and Applications Center.)