Ocean warming on the rise

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Bruce Miller, CSIRO

Increased scientific confidence that ocean observations are accurately reflecting rising global temperatures is central to new Australian research published today in the journal, Nature. The team of Australian and US climate researchers found the world's oceans warmed and rose at a rate 50 per cent faster in the last four decades of the 20th century than documented in the 2007 Intergovernmental Panel on Climate Change Report (IPCC AR4).

The research gives significantly greater credibility to the way climate models simulate the degree of warming in the world's oceans – a key indicator of sea-level rise and climate change.

The results were added to other recent estimates of contributions to sea-level rise, including glaciers, ice caps, Greenland and Antarctic ice sheets, and thermal expansion changes in the deep ocean. The sum of all contributions is more consistent with observed sea-level rise than earlier studies.

"For the first time, we can provide a reasonable account of the processes causing the rate of global sea-level rise over the past four decades – a puzzle that has led to a lot of scientific discussion since the 2001 IPCC report but with no significant advances until now," says CSIRO Wealth from Oceans National Research Flagship scientist, Dr Catia Domingues, from the Centre for Australian Weather and Climate Research.

"Following the review of millions of ocean measurements, predominantly from expendable instruments probing the upper 700 metres of the ocean, we were able to more accurately estimate upper-ocean warming, and the related thermal expansion and sea-level rise.

"We show that the rate of ocean warming from 1961 to 2003 is about 50 per cent larger than previously reported," Dr Domingues says.,The new estimates also more closely agree with the models used in the IPCC 2007 report.

"Our results are important for the climate modelling community because they boost confidence in the climate models used for projections of global sea-level rise resulting from the accumulation of heat in the oceans. These projections will, in turn, assist in planning to minimise the impacts and in developing adaptation strategies."

Central to unlocking more accurate estimates of upper-ocean warming and sea-level rise was research completed earlier this year by CSIRO's Dr Susan Wijffels and NASA's Dr Josh Willis, among others, and soon to be published in the American Meteorological Society's Journal of Climate. This study provided ways of correcting small but systematic biases recently discovered in 70 per cent of measurements in the global ocean observing system.

Dr Wijffels says the results also indicate an ongoing need for careful quality control of observational data and continuous monitoring of the oceans using diverse observations that can be checked against each other.

Dr Domingues says the oceans store more than 90 per cent of the heat in the Earth's climate system and act as a temporary buffer against the effects of climate change.

"Detailed comparisons of these new observational estimates with climate models will be required to refine our current understanding and improve projections of the regional distribution of sea-level rise," she says.

Source: CSIRO Australia