Cool Los Altos

Climate Change: Science

The Earth's atmosphere is a thin insulating layer around the planet that protects life as we know it. Gases in the atmosphere, including carbon dioxide and methane, trap some of the sun's energy as it bounces off the Earth, keeping the average surface temperature of the Earth around 60 degrees F. Without this "greenhouse effect" the Earth could not sustain life.

Global warming is a rise in the Earth's temperature resulting from an increase in heat-trapping gases in the atmosphere. The Intergovernmental Panel on Climate Change (IPCC), a network of more than 2500 scientists from 130 countries and the body responsible for sorting out the evidence on global warming, concludes in its latest Report that "warming of the climate system is unequivocal" and that human activity “very likely” causes most of the global warming. Thus, human activity, such as the burning of fossil fuels, intensive agriculture, and waste generation, release heat-trapping gases into the atmosphere that are fundamentally changing our climate system.

Additional IPCC Findings on Recent Climate Change

Rising Temperatures

  • The Earth has warmed about 0.74°C (1.3°F) in the last 100 years ending in 2005.
  • Eleven of the last 12 years (1995-2006) rank among the 12 hottest years on record
  • Over the last 50 years, “cold days, cold nights, and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent.”

Melting and Thawing

  • The Northern Hemisphere has lost 7% of the maximum area covered by seasonally frozen ground since 1900.
  • Mountain glaciers and snow cover have declined in both hemispheres.
  • Satellite data since 1978 show that the annual average Arctic sea ice extent has shrunk by 7% during the summer per decade.

Rising Sea Levels

  • Since 1961, the world’s oceans have been absorbing more than 80 percent of the heat added to the climate, causing sea water to expand and contributing to rising sea levels. The sea level rose at a faster rate between 1993 and 2003.
  • Melting glaciers and losses from the Greenland and Antarctic ice sheets have very likely contributed to recent sea-level rise.

Increasingly Extreme Weather (storms, precipitation, drought)

  • The intensity of hurricanes in the North Atlantic has increased since the 1970s, which correlates with increases in sea surface temperatures.
  • Storms with heavy precipitation have increased in frequency over most land areas.
  • Droughts have become longer and more intense, and have affected larger areas since the 1970s, especially in the tropics and subtropics.

Current CO2 concentrations are higher than any seen in almost a million years. Furthermore, the rate of global climate change we are currently experiencing is greater than that during any time since the end of the last ice age.

The IPCC projects that the Earth's atmosphere near the surface will warm an additional amount somewhere between 1 and 6°C (2°F -11.5°F) by the end of this century. It also projected that sea levels will most likely to rise by 28-43cm, and climate change will continue to influence the intensity of tropical storms.

"It is the rapid rate of change of temperature relative to previous eras, habitat fragmentation, and a billion peopole tightly locked into national boundaries and living at nutritional margins, that together define the unique and serious problem of global warming that we are facing today."
-- Stephen H. Schneider, Lead Author Working Group II, IPCC in a letter to Los Altos City Council.