September 27, 2013

Scientists are 95 percent certain that humans are the “dominant cause” of global warming, the authors of a landmark report from the Intergovernmental Panel on Climate Change (IPCC) announced today. The authors of the report stated emphatically that global warming is “unequivocal” on the ground, in the air, and in the oceans; and that since the 1950′s, many of the observed changes in the climate system are “unprecedented over decades to millennia.”

The glacier Qori Kalis in the Andes Mountains in Peru melted substantially between 1983 and 2000. According to scientists at the Byrd Polar Research Center of Ohio State University, this melting provides a clear sign of global warming (© Lonnie G. Thompson, Byrd Polar Research Center, Ohio State University).

IPCC Co-chair Qin Dahe wrote, “Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and that concentrations of greenhouse gases have increased.” Speaking today at a news conference in Stockholm, Co-chair Thomas Stocker declared that climate change “challenges the two primary resources of humans and ecosystems, land and water. In short, it threatens our planet, our only home.” Both scientists contend that since 1950, humans are clearly responsible for more than half of the observed increase in temperatures through the burning of fossil fuels.

The IPCC report downplayed a so-called pause in the increase in temperatures in the period since 1998. The authors pointed out that this period began with a very hot El Nino year: “Trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”

The authors of the report warned that continued emissions of greenhouse gases at current levels would trigger further warming and changes to all aspects of the world’s climate system. They predict that continued emissions of greenhouse gases at current levels could result in sea levels rising by the end of this century by 10 inches (26 centimeters) at the low end and 32 inches (82 centimeters) at the high end. They conclude that to halt or even forestall these changes will require “substantial and sustained reductions of greenhouse gas emissions.”

Additional World Book articles:

• The Great Meltdown (a special report)
• Methane (a special report)
• Meltdown: Climate Change in the Arctic (a special report)
• Probing the History of Climate Change  (a special report)
• What We Know About Climate Change (a special report)

September 9, 2013

Human activities influenced at least some of the extreme weather events that occurred across the world in 2012, according to new research on the causes of 12 events that occurred on 5 continents and in the Arctic. The research, Explaining Extreme Events of 2012 from a Climate Perspective, included 19 studies conducted by 78 scientists working in 11 countries. All of the events would have occurred even without rising global temperatures, with “natural weather and climate fluctuations” playing “a key role in the intensity and evolution” of the events, the scientists concluded. However, they also reported compelling evidence that human activity—particularly the release of large amounts of carbon dioxide and other heat-trapping greenhouse gases from the burning of fossil fuels—contributed to about half of the events.

Earth’s average surface temperature rose by about 1.4 Fahrenheit degrees (0.76 Celsius degree) from the mid-1800′s to the early 2000′s. Researchers have also found that most of the temperature increase occurred from the mid-1900′s to the 2000′s. Natural processes have caused Earth’s climate to change in the distant past. But scientists have found strong, clear evidence that human activities have caused most of the warming since the mid-1900′s.

A new reports suggests that coastal flooding from ocean storms will increase because of global warming. (AP/Wide World)

The difficulty in determining whether and to what degree human activities are influencing storms, heat waves, and other extreme weather events has made scientists cautious about linking global warming to any particular event. Recent advances in computer modeling and a greater understanding of climate data, however, have greatly improved scientists’ ability to distinguish natural weather factors from human-related factors. The new report has added to scientists’ understanding of the impact that climate change “adds, or doesn’t add, to any extreme event,” said Thomas R. Karl, director of the National Climatic Data Center in Asheville, North Carolina.

The scientists concluded that natural weather patterns were responsible for heavy rains that caused devastating floods in India, China, and Japan and for high summer rainfall in the United Kingdom in summer 2012. In addition, climate change only slightly influenced extreme rains in New Zealand in December 2011 and in Australia from October 2011 to March 2012.

In the United States, climate change had little effect on the drought that struck the midwestern United States in the summer, the scientists reported. However, human activities played a role in the accompanying heat waves that struck that region as well as the eastern United States. Temperatures during these hot spells are higher now than in the past and occur four times as often. The authors of the study also suggested that global warming will increasingly lead to more coastal flooding like that which occurred during Hurricane Sandy.

Some of the strongest evidence involved the record loss of sea ice in the Arctic. The scientists concluded that this loss resulted “primarily from the melting of younger, thin ice from a warmed atmosphere and ocean. This cannot be explained by natural variability alone.”

Additional World Book articles:

• The Great Meltdown (a special report)
• Methane (a special report)
• Meltdown: Climate Change in the Arctic (a special report)
• Probing the History of Climate Change (a special report)
• Twisted–More Terrible Storms (a special report)
• What We Know About Global Warming (a special report)

November 20, 2012

Greenhouse gases have reached unprecedented levels, according to a report by the United Nations (UN) World Meteorological Organization. The report found that the global average of carbon dioxide (CO2) in the atmosphere reached 390.9 parts per million (ppm) in 2011. The concentration of CO2 in the atmosphere has grown by about 40 percent since the year 1750, at the beginning of the Industrial Revolution.

CO2 is released chiefly by burning such fossil fuels as coal and oil. China now produces more CO2 pollution than any other country, followed closely by the United States.

Climate scientists have found that increasing concentrations of CO2 and other greenhouse gases are the chief cause of global warming. Rising concentrations of these gases trap more of the energy in sunlight at Earth’s surface. Thus, the gases act somewhat like the walls of a greenhouse, which allow in light but prevent heat from escaping. As levels of greenhouse gases rise, they cause a gradual increase in Earth’s average surface temperatures known as global warming.

High levels of heat-trapping greenhouse gases are being released into the atmosphere by manufacturing and other human activities. (© age fotostock/SuperStock)

Global warming has already increased Earth’s average surface temperature by about 1.4 Fahrenheit degrees (0.76 Celsius degrees) since the mid-1800′s. Scientists predict that the average surface temperature will rise an additional 2.0 to 11.5 Fahrenheit degrees (1.1 to 6.4 Celsius degrees) by 2100. Climate scientists warn that severe global warming will do great damage to the natural environment and human society.

The UN report also found increases in greenhouse gases apart from CO2. The second most important greenhouse gas is methane, which is produced by natural gas extraction, agriculture, and landfills, among other human-made sources. Methane reached 1,813 parts per billion in 2011, an increase of about 259 percent above its level in 1750. Although the concentration of methane is much lower than that of CO2, methane is a more powerful greenhouse gas.

In May 2012, atmospheric concentrations of CO2 briefly surpassed 400 ppm in the Arctic, according to the National Oceanic and Atmospheric Administration. CO2 concentrations vary by latitude and season, mostly because growing plants take up significant amounts of CO2 through photosynthesis. Scientists expect average global CO2 concentrations to reach 400 ppm no later than 2016. The 400 ppm threshold has mostly symbolic significance, but many climate scientists warn that CO2 concentrations over 400 ppm will cause damaging levels of global warming.

Addtional World Book articles:

• Carbon footprint
• Intergovernmental Panel on Climate Change
• Kyoto Protocol
• Methane: Another Greenhouse Troublemaker (a Special Report)
• The Great Meltdown (a Special Report)

Dec. 6, 2011

The amount of heat-trapping carbon dioxide (CO₂) being pumped into Earth’s atmosphere jumped to record levels in 2010, according to the annual report by the Global Carbon Project (GCP). The GCP is an international collaboration of scientific organizations. The report said that the emissions rose by 5.9 percent, more than one-half billion tons of carbon. It was the largest annual increase since scientists began taking precise measurements of CO₂ emissions in 1959.

The disappearance of sea ice poses a threat to the wildlife of the Arctic Ocean. These satellite photographs show the extent of summer sea ice in 1979 (left) and 2005 (right). The ice covering has decreased as a result of global warming, an increase in the average temperature at Earth's surface. NASA

GCP scientists also calculated that the 2010 rate was almost certainly the largest yearly jump since the beginning of the Industrial Revolution in 1750. Based on these numbers, the scientists calculated that the concentration of CO₂ in the atmosphere has reached its highest level in the past 800,000 years. CO₂ emissions had dropped slightly in 2009 because the worldwide financial crisis had reduced manufacturing. The GCP scientists calculated that about half of the emissions remained in the atmosphere. The rest was absorbed by the ocean and bodies of water on land as part of the carbon cycle.

Other highlights of the report included the following:

• China, India, and the United States led the world in CO₂ emissions in 2010;
• China accounted for 24.6 percent of total emissions, compared with 16.4 percent for the United States;
• A large percentage of the emissions came from the burning of fossil fuels in power plants and factories and the production of cement;
• Annual CO₂ emissions from burning fossil fuels have increased by 49 percent since 1990, the base year used by the Kyoto Protocol for calculating reductions.

Additional World Book articles:

• Global warming
• The Great Meltdown (a Special Report)
• The Ocean’s Changing Chemistry: Tipping the Balance? (a Special Report)