CLIMATE CHANGE: by Peter WestmoreNews Weekly
Rising sea levels: IPCC's latest scare campaign
, February 2, 2013
Faced with the inconvenient truth that there has been no net increase in global temperatures since 1998 — despite the steady rise in CO2 levels in the atmosphere — the UN Intergovernmental Panel on Climate Change (IPCC) has cast around for other effects of climate change, including catastrophic climate events such as floods and heatwaves, and rising sea levels which threaten the future of coastal communities.
At the recent IPCC meeting in Hobart, Tasmania, which took place within days of a heatwave and the most severe bushfires in Tasmania since 2006, the IPCC chairman, Dr Rajendra Pachauri, said that climate change was characterised by extreme climate events, and the IPCC foreshadowed the change in direction by including a new chapter in its next report on rising sea levels.
The lead author of the new chapter on rising sea levels is Dr John Church of the CSIRO.
Dr Church told the Hobart Mercury that rising sea level is clearly linked to climate change. He warned, “The sea level is rising, the rate of the rise has increased and will continue to increase” (January 16, 2013).
He said the rate had increased from a few tenths of a millimetre a year before the 20th century to more than 3mm a year in the past 20 years. “It’s clear the rate of sea level rise has already increased,” he told the Mercury.
“Whether that 3mm is a further acceleration or not is yet unclear, but we do expect a further acceleration during the 21st century and it’s clearly linked to greater levels of greenhouse gases.”
To get this in perspective, a rise in average sea levels of 3mm a year would require the same increase over a 300-year period to raise sea levels by 1 metre, which is about the amplitude of average daily tidal movements.
Another problem with the figures is that global tidal data have only been available for the past 20 years, since satellite altimeters have been collecting the data. Earlier figures are an extrapolation from port sea level data, for which most records go back 100 years at most.
Even earlier estimates come from sediment cores from salt marshes in selected locations around the world. Like tree-ring data, these are less reliable than satellite data for a variety of reasons.
Some of the causes of apparent sea-level rises are discussed on the website of the CSIRO’s own Marine and Atmospheric Research Centre (www.cmar.csiro.au).
These causes include rising and falling land levels, due to both short-term and long-term geological factors (including rising of the land mass in North America, Northern Europe and North Asia as a result of the last Ice Age). Additionally, wave erosion of the shore-line, severity of storm surges and tides also affect the local sea level.
Sea levels are also affected by ocean temperatures, including the annual warming/cooling cycle as the oceans warm and expand in summer and cool and contract in the winter. Thus sea levels in each hemisphere are higher in summer and lower in winter.
In addition, there is an increase of water stored on land in the northern hemisphere winter and thus less in the ocean, leading to a lower global average sea level in the northern winter.
Other changes are related to the weather patterns in the ocean-atmosphere system, which in turn produce changes in ocean currents and thus changes in sea level. These are still poorly understood, but it is known that the El Niño-La Niña events cause fluctuations of up to 300 mm in local sea levels from the eastern Indian Ocean to the eastern Pacific Ocean, which is 100 times the “alarming” 3mm a year rise which so concerns the IPCC.
Additionally, the water from melted snow and ice which flows into the seas will lift global sea levels, although how much of this is due to climate change is uncertain.
Despite Dr Church’s claim above, the assessment of the Marine and Atmospheric Research Centre is far more balanced.
It says: “The ice sheets of Greenland and Antarctica have the potential to make the largest contribution to sea level rise, but they are also the greatest source of uncertainty. Since 1990 there has been increased snow accumulation at high elevation on the Greenland Ice Sheet, while at lower elevation there has been more widespread surface melting and a significant increase in the flow of outlet glaciers.
“The net result is a decrease in the mass of the Greenland Ice Sheet — a positive contribution to sea level rise.
“For the Antarctic Ice Sheet, the uncertainty is greater. There are insufficient data to make direct estimates for the preceding decades. At present, the mass gain of the Antarctic Ice Sheet due to increased thickening of the East Antarctic Ice Sheet does not appear to compensate for the mass loss due to the increased glacier flow on the Antarctic Peninsula and the West Antarctic Ice Sheet.”
The satellite data do indeed show a 3mm annual rise in average ocean levels over the past 20 years, but the data do not show any acceleration, and the time period is too short to reach any definite conclusions.
The IPCC’s claim that ocean levels are rising alarmingly due to climate change is simply untrue.