What is climate change?
The phrase 'climate change' refers to a change in a measurable property of the climate (eg average temperature) that persists for an extended period, typically decades or longer. Such changes can be due to natural variability or to human activity.
Both natural and human induced changes are of interest - without an understanding of natural climate variability it would be impossible to investigate the impact of human behaviour. That said, many people assume that the phrase 'climate change' refers only to human induced change
Is the climate really changing?
Yes it is. We are experiencing an upward trend in average surface and ocean temperatures as well as rising sea levels and widespread melting of snow and ice:
 |
The eleven years 1995-2006 rank amongst the twelve warmest years since records of global surface temperature began in 1850. |
|
Melting ice and rising temperatures have caused the global average sea level to rise at an average rate of 3.1 mm / yr since 1993. |
|
More than 3 million tonnes of global ice melt every five minutes. That's a 144m x 144m x 144m cube. Satellite data since 1978 show that annual average Arctic sea ice has shrunk by 2.7% per decade. The summer ice is predicted to disappear completely between 2013 and 2040; a state not seen on earth for more than a million years. |
Other Indicators
)
Source: Intergovernmental Panel on Climate Change, Fourth Assessment, Climate Change 2004: IPCC AR4 Synthesis Report.
- The retreat of mountain glaciers is superbly captured in these photographs (right) of the Triftgletscher glacier comparing 1948 with 2002 and 2006. Even in the four year period 2002 and 2006 the contraction is alarming.
- The flow rates of major rivers such as the Ganges and the Niger are decreasing, threatening the supply of food and water to millions of people in developing nations.
- Many natural systems are being affected by regional climate changes: plants flower earlier, birds migrate at different times, plants and animals shift higher up the mountain.
- Extreme weather events including lowland floods, hurricanes and heatwaves appear to be occurring more frequently.