The report summary also says that global warming is likely to continue for centuries, and that it is already too late to stop some of the serious consequences it will bring—even if mankind could somehow hold the line on greenhouse gas emissions worldwide starting today.
Despite those grim conclusions, however, the report does say that there is still time to slow global warming and to lessen many of its most severe consequences if we act quickly. At the same time, the IPCC report avoids prescribing specific strategies, leaving that to policymakers worldwide, the audience for which the report summary was prepared.
This article answers some of the most common questions about the IPCC report and its predictions for the future of our planet.
Q: What are the expected consequences of global warming based on the summary of the fourth IPCC assessment of climate change science?
A: Global temperatures are expected to increase 3.5 to 8 degrees Fahrenheit by 2050, and there is a 1-in-10 chance that the increase could be far worse, a risk that many experts believe is too great to ignore.
Rising temperatures will alter global weather patterns that have a direct effect on water supplies and agriculture. Deserts will expand, the frequency and severity of droughts and deadly heat waves will increase, and snow will disappear in most areas—except on the very highest mountain peaks.
Sea levels worldwide are expected to rise between 7 and 23 inches by 2100, and will continue to rise for at least the next 1,000 years.
Fierce storms, such as hurricanes, will become more frequent and more floods will occur, due to rising sea levels and heavier rainfall in some areas.
Continuing global warming will also lead to a rise in many diseases that are deadly to humans. Flooding will contaminate water supplies in some areas, giving rise to infectious diseases. Rising temperatures will also increase the range and breeding grounds of mosquitoes and other disease-bearing insects, exposing more people to diseases such as malaria, dengue fever, yellow fever and encephalitis.
Q: What does the IPCC report say about the relationship between global warming and human activity?
A: In the strongest language ever used by the IPCC, the report says that human activity “very likely” has been the primary cause of global warming since 1950. (The term “very likely” indicates more than 90 percent certainty.)
The report summary also says that human activity has been a major contributor to climate change since the Industrial Revolution, which began around 1750.
Global concentrations of carbon dioxide, methane and nitrous oxide—three of the most notable greenhouse gases—have increased significantly over the past 250 years as direct result of human activities. Concentrations of carbon dioxide and other greenhouse gases now far exceed any found during ice core research spanning the past 650,000 years.
The increase of carbon dioxide is due primarily to the use of fossil fuels, such as oil and coal, and changes in land use, such as cutting down forests to make way for farming, housing and other development. Increases in methane and nitrous oxide are primarily due to agriculture.
Q: What does the report say about the risks of rising sea levels due to global warming?
A: Sea levels worldwide are expected to rise between 7 and 23 inches by 2100, and will continue to rise for at least the next 1,000 years. By comparison, global sea levels rose 6 to 9 inches in the 20th century, so the effects of global warming on sea levels are clearly accelerating.
Rising sea levels will create millions of environmental refugees as people are forced to leave their homes in coastal areas. Many nations will be unequipped to cope with the waves of immigrants looking for new homes.
Increased levels of carbon dioxide in the atmosphere will change the pH balance of seawater, making it slightly more acidic. Although the oceans will remain alkaline, marine biologists predict that a shift toward greater acidity could threaten the survival of coral reefs and plankton—an essential and fundamental link in the marine food chain.
Even a moderate increase in the build up of greenhouse gases in the atmosphere could easily push average global temperatures to levels last seen 125,000 years ago during a warm period between two ice ages. At that time, sea levels were 12 to 20 feet higher than they are today. Much of the water from that earlier period is now frozen in Greenland and Antarctica, but many of those ice fields are beginning to melt.
Because scientists are not certain how quickly polar ice will melt, the estimates of sea level increases in the report are based on how much warming oceans will expand and do not take into account anticipated runoff from melting ice on land in Greenland and the polar regions.
To learn more about the report's conclusions and the steps needed to slow global warming, see page 2.