by Dr Jim Salinger, Auckland climate scientist,
2012 Lorry Lokey visiting professor at Stanford University
YOUR editorial of Saturday 13 April 2013 titled “Climate Change Express is behind schedule” points to the 30 March 2013 edition of The Economist which suggests that man-made climate change is not as bad a threat as it appeared and global warming has stalled.
Unfortunately the Economist conclusions are flawed and have omitted critical recent research.
The global mean surface temperature is only one measure of the increase in heat content of the earth and atmosphere. We must view a whole basket of evidence to conclude whether the earth/atmosphere is continuing to warm or not.
The summer season just past over Australasia has been a perfect analogue of what the climate models are projecting for mid-century: record-breaking summer temperatures in Australia and the surrounding seas, devastating bushfires over southern Australia, floods in Queensland, and the trend to a more Mediterranean climate for the North Island with a historic drought.
Last year, on September 16 2012, Arctic sea ice reached its minimum extent for the year of 3.41 million square kilometres — the lowest in the satellite record since 1979, and reinforcing the long-term downward trend in Arctic ice extent.
Mountain glacier extent is monitored by the World Glacier Monitoring Service based in Switzerland. The inventory provides sufficient data for calculation of glacier lengths and mass balance where measurements are available. They have calculated cumulative trends in glacier mass in metres-of-water-equivalent in 10 mountain ranges around the world.
Ice thinning since the mid-1990s has been dramatic, as shown in the diagram above, with about 8 metres thickness lost in water equivalents from 1995 to 2009. Since the late 1950s, glaciers have thinned 14 metres in water equivalent.
In response to The Economist, the global climate system has natural internal variability or natural oscillations in climate such as those associated with the El Niño or La Niña phenomenon. Since 1998 there have been six La Niña seasons, which can cause surface global temperatures to be up to 1°C cooler than the normal.
More importantly, the Intergovernmental Panel on Climate Change has concluded that about 90 percent of overall heating goes into warming the oceans, which cover over two-thirds of the global surface. In comparison only 2 percent heats the atmosphere. In a study published last month, a leading New Zealand scientist and others at the US National Center for Atmospheric Research concluded that about 30 percent of the warming in the last decade has occurred below 700 metres in the deeper ocean. The study notes that recent warming at these depths has been unparalleled.
In a paper in Nature Climate Change of 8 April 2013, a team of European scientists found the oceans took up more warmth from the air from around the year 2000. They found that most of this excess energy was absorbed in the top 700 metres of the ocean at the onset of the warming pause, 65 percent of it in the tropical Pacific and Atlantic oceans.
Another recent study suggests that during 2000-2010 more burning of coal in Asia and recent moderate volcanic eruptions ejecting sulphate have increased the aerosol amounts in the atmosphere. These fine particles block some sunlight that heats up the earth’s surface and atmosphere and may have offset some of the expected warming in global temperatures. These short-term fluctuations in aerosols are not catered for in the scenarios that drive global climate models.
These and other studies suggest that global warming is alive and well, and the expected magnitude of temperature increase this century is undiminished around 3 degrees. It is still very urgent to decrease our carbon emissions from fossil fuels to the atmosphere.