A UN panel said Friday it was more certain than ever that humans were causing global warming and predicted temperatures would rise by 0.3 to 4.8 degrees Celsius (0.5-8.6 degrees Fahrenheit) this century.
The Intergovernmental Panel on Climate Change (IPCC) also projected sea levels would rise by between 26 and 82 centimetres (10.4 and 32.8 inches) by 2100, according to a summary of the first volume in a long-awaited review.
The Nobel-winning group said it was "extremely likely," a term meaning it was 95-percent convinced, that humans caused more than half of the warming observed over the past 60 years.
In its last report in 2007, the panel had rated its conviction at 90 percent.
The new document is the first volume in a trilogy seeking to summarise the status of global warming and its impacts.
The IPCC has delivered four previous assessment reports in its 25-year history.
Each edition has pounded out an ever-louder drumbeat to warn that temperatures are rising and the risk to the climate system—in drought, floods, storms and rising seas—is accentuating.
The panel's projections for 2100 are based on computer models of trends in heat-trapping greenhouse gas emissions, especially from coal, oil and gas, which provide the backbone of the energy supply today.
The most optimistic of four warming scenarios sees an average temperature rise of 1.0 C (1.8 F) by 2100 over 2000 levels, ranging from 0.3 to 1.7 C (0.5-3.1 F). This is the only scenario that can safely meet a UN target of 2 C (3.6 F) which also factors in warming from the start of the Industrial Revolution to 2000.
The highest IPCC scenario has an average additional warming this century of 3.7 C (6.7 F), ranging from 2.6 C (4.7 F) to a 4.8 C (8.6 F).
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