On February 2, 2007, the world received its strongest warning yet that global warming is real, and is happening now. The Intergovernmental Panel on Climate Change (IPCC) released Climate Change 2007, its latest assessment on the state of the Earth’s climate. The report states that global warming is very likely, 90% to 99% certain. According to the report, if we continue on the current path, major changes in the Earth’s environment are on the way.
The IPCC was cofounded in 1988 by the United Nations Environmental Programme and the World Meteorological Organization. Its mission: to assess—without scientific, economic, or country bias—whether the Earth’s climate is changing. The members of the committee come from many countries and different academic disciplines. The group develops its reports from many reliable sources. These include published peer-reviewed articles and data collected by industries and governments. The IPCC is very careful to make sure that many technically valid viewpoints are assessed for its reports. The panel has issued four climate change reports, in 1990, 1995, 2001, and 2007. Along with these documents, the IPCC releases a Summary for Policymakers, which outlines key issues in the reports.
Previous reports indicated that climate change was occurring. In particular, the 2001 report indicated that global warming was likely—66% to 90% certain.
According to the 2007 report, the warming trend appears more evident than ever. Concentrations of CO2 (the most important greenhouse gas) increased at a faster rate from 1995 to 2005 than they did from 1960 to 1995. The report points to human activities as the source of all this added CO2. Most of the CO2 is from the burning of fossil fuels but changed land use—the disappearance of forests—is also a significant factor. Concentrations of the other greenhouse gases, including methane and nitrous oxide, have also increased.
Researchers have been able to get measurements of atmospheric gases going back many years by analyzing ice cores drilled from glaciers in places such as Greenland and Antarctica, where the snow never melts off each year. Snow carries particles from the air when it falls, and as it compacts, air bubbles from the time it fell are trapped. Analysis of ice cores dating back 10,000 years shows a steep increase in greenhouse gases since the 1760s. This is the point in time when modern industry began to develop, with coal and later oil as the sources of power.
The changes in the climate reflect the increases in greenhouse gases. Between 1995 and 2006 the world had 11 of the 12 warmest years on record for global surface temperature. The warming trend over the last 50 years is nearly twice that of the last 100 years. There are many indicators that show the warming trend. Mountain glaciers and snow cover are decreasing. The ice sheets in Greenland and Antarctica are shrinking in places. Sea level continues to rise, and the average temperature of the ocean is on the increase. The climate is changing in other ways. Droughts are longer and more intense, and affect wider areas. Heavy precipitation events are more frequent. The 2007 report indicates that these changes are greater than the variables seen in climate over the past 1,300 years, and they are on a par with what occurred during the last ice age, about 125,000 years ago. The IPCC concludes that the increased concentrations of greenhouse gases are behind these changes in climate.
According to the 2007 report, we need to cap CO2 emissions at 450 parts per million (ppm) to prevent the most major of changes in the world’s climate. This means that governments, businesses, and individuals need to make significant efforts to change the way they (and we) do things, to lower CO2 emissions.
The report strongly states that if greenhouse gas emissions continue at the current pace or at an even faster pace, further warming will occur. This in turn will cause many changes in global climate. Surface temperatures could rise as much as 2.4 to 6.4 C degrees (4.3 to 11.5 F degrees) if emissions grow faster than the current rate. Sea levels will rise, and weather patterns will change significantly. These changes include more intense storms and even broader and longer droughts.
Even if emissions are cut to and maintained at a level below the 450 ppm cap, global warming will continue for a while, until the Earth’s environment stabilizes.
Illustration courtesy IPCC
These graphs, from the IPCC 2007 Summary for Policymakers report, compare real average temperatures on the continents and worldwide from 1901 to 2000 with different climate simulations. The black line shows actual temperatures from this period. The blue band represents simulations from climate models that include changes from solar activities (such as solar flares) and volcanoes. The pink band shows simulations from climate models that include natural changes (as in the blue band) plus changes from other sources. Notice that the pink band follows the trend of what has actually occurred. This leads us to the conclusion that the increased temperature around the world is due to outside influences, namely greenhouse gas emissions from human activities.
Illustration courtesy IPCC
This figure, from the IPCC 2007 Summary for Policymakers report, shows projected surface temperature changes for the periods 2020-2029 and 2090-2099. Three different economic and population growth models were used as the basis for these diagrams. The top row, B1, posits a population that peaks in mid-century and then declines, with the development of a service and information economy, which includes cleaner and more efficient technologies. This scenario causes the least changes in temperature. Model A1B has the same population curve as B1. However, there is rapid worldwide economic growth, with a variety of resources providing energy. This scenario shows moderate changes in temperature. The A2 model has a continuously increasing population with all regions of the world focused on their own economies and technologies, at each region’s own pace. This scenario shows the largest temperature increase. None of these scenarios include specific initiatives to control emissions; they project what could happen if things are left as is. The models are based on Atmosphere-Ocean General Circulation Multi-Models.
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