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Saturday 21 March 2009

by: Michel Jarraud

    Data collected over the past 150 years by the 188 members of the World Meteorological Organization (WMO) through observing networks of tens of thousands of stations on land, at sea, in the air and from constellations of weather and climate satellites lead to an unequivocal conclusion: The observed increase in global surface temperatures is a manifestation of global warming. Warming has accelerated particularly in the past 20 years.

    It is a misinterpretation of the data and of scientific knowledge to point to one year as the warmest on record - as was done in a recent Post column ["Dark Green Doomsayers," George F. Will, op-ed, Feb. 15] - and then to extrapolate that cooler subsequent years invalidate the reality of global warming and its effects.

    The difference between climate variability and climate change is critical, not just for scientists or those engaging in policy debates about warming. Just as one cold snap does not change the global warming trend, one heat wave does not reinforce it. Since the beginning of the 20th century, the global average surface temperature has risen 1.33 degrees Fahrenheit.

    Evidence of global warming has been documented in widespread decreases in snow cover, sea ice and glaciers. The 11 warmest years on record occurred in the past 13 years.

    While variations occur throughout the temperature record, shorter-term variations do not contradict the overwhelming long-term increase in global surface temperatures since 1850, when reliable meteorological recordkeeping began. Year to year, we may observe in some parts of the world colder or warmer episodes than in other parts, leading to record low or high temperatures. This regional climate variability does not disprove long-term climate change. While 2008 was slightly cooler than 2007, partially due to a La NiÒa event, it was nonetheless the 10th-warmest year on record.

    The Intergovernmental Panel on Climate Change, co-sponsored by the WMO, has confirmed through observations and increasingly sophisticated and realistic models that regional variability has increased and will continue to increase as global surface temperatures rise. This is likely to result in more weather and climate extremes, such as droughts, floods, storms and heat waves. Responding to these challenges will require the collaborative efforts of all countries and of scientists in multiple disciplines to develop adaptation strategies to reduce the risk of disaster. This topic is scheduled for discussion at the World Climate Conference-3 beginning Aug. 31 in Geneva.

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    Michel Jarraud is secretary general of the World Meteorological Organization, Geneva

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