Climate: Growing certainties on warming and human role

Climate: Growing certainties on warming and human role

PARIS - Over the past 23 years, UN scientists have issued progressively stronger assertions about climate change. They have moved from a sketchy warning that heat-trapping carbon gases emitted by fossil fuels will cause a "greenhouse" effect to the conviction that this effect is now having an impact on Earth's climate.

Following are extracts from the Intergovernment Panel on Climate Change's assessment reports, the latest of which will be published from Friday.

First Assessment Report (1990)

"... emissions resulting from human activities are substantially increasing atmospheric concentrations of greenhouse gases... "These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface."

Second Assessment Report (1995)

"Most of these studies have detected a significant change and show that the observed warming trend is unlikely to be entirely natural in origin... "... the balance of evidence suggests that there is a discernible human influence on global climate.

"... the average rate of warming [in projections for the 21st century] would probably be greater than any seen in the last 10,000 years, but the actual annual to decadal changes would include considerable natural variability."

Third Assessment Report (2001)

"There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. "... the projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years, based on paleoclimate data." The report said the global average temperature had risen by 0.6 degrees Celsius (1.08 degrees Fahrenheit) between 1901 and 2000. Human activity was "likely" to be the cause of warming, a term meaning a probability of more than 66 per cent.

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