Understanding global climate change science

The global record shows that since the late 19th century temperatures averaged across the globe have increased by around 0.6 degrees Celsius, with a good part of that increase occurring during the 1990s.

As the history of the ice ages shows, Earth's temperature has swung widely in the past, long before humans could have affected the climate. Still, climate scientists say the evidence is strong that humans are responsible for at least some of the warming since early in the 20th century.

Climate scientists also have strong reasons for saying that as humans continue adding gasses to the air, warming is likely to continue through this century.

Many questions remain to be answered. These include how much of the warming to date has been caused by humans, how much is natural. Only estimates offering wide ranges of how much the climate should warm during this century are available. Many questions remain about the effects of a generally warmer climate.

While climate scientists don't agree on all of the points made, three reports issued during 2001 by working groups (or committees) of the Intergovernmental Panel on Climate Change (IPCC) are the best place to begin understanding the current state of climate change science.

The January report on "Climate Change 2001: The Scientific Basis," from Working Group 1, which was issued in January 2001, covers the basic science of climate change. The other reports are from Working Group 2, "Climate Change 2001: Impacts, Adaptation and Vulnerability, " and Working Group 3, "Climate Change 2001: Mitigation," came out later in 2001.

The January 2001 report from Working Group 1 said that by the end of this century, average global temperatures should increase by 1.4 to 5.6 degrees Celsius. Many press reports at the time focused on this high-end of this range and the disasters it could bring. But, both the high and low range of the increase are the least likely to happen.

The report lists "very likely" 21st century changes as:

• Higher daily maximum temperatures and more hot days over nearly all of the Earth's land.

• Warmer overnight low temperatures.

• Fewer cold days and frost days over nearly all land

• Reduced differences between daily highs and lows over nearly all land.

• More intense rain or snow storms over many areas.

• A higher risk of summer droughts over inland areas of the middle-latitude continents.

The panel also says that hurricanes, typhoons, and Indian Ocean and South Pacific cyclones are likely to produce higher winds and heavier rain in some areas, but there's no way to tell whether the frequency and locations of these storms could change.

The report notes that no global changes have been noted during the 20th century in terms of the numbers of storms or their strength. "No systematic changes in the frequency of tornadoes, thunder days, or hail events are evident in the limited areas analyzed."

While snow cover and sea ice in the Northern Hemisphere are expected to continue decreasing, and glaciers should continue retreating, (as they have during the 20th century) the Antarctic ice sheet should grow. This is because warmer air can hold more humidity, which will increase the amount of snow in Antarctica. This in turn, will offset some of the water being added by melting glaciers and some melting of the Greenland ice cap.

Copyright © Malta Weather Services 2003