January 18, 2016

expert reaction to rising ocean heat uptake

Publishing in the journal Nature a group of scientists has looked at heat of the world’s oceans since the industrial revolution and report that around half of the increases in temperature have occurred in recent decades which a third of this accumulated heat being at depths below 700m.

The SMC also produced a Briefing Note on the ‘global warming slowdown’.

Prof. Jonathan Gregory, University of Reading, said:

“The paper confirms that ocean heat uptake has been proceeding unabated, as previous analyses have shown, during the recent slowdown in surface warming. The agreement between ocean observations and CMIP5 models gives us more confidence in climate projections of ocean heat uptake and the associated sea level rise from thermal expansion.

“The authors find that while the 0-700 metre layer dominates the total ocean heat uptake over the historical period, the deeper layers are playing an increasingly important role. That is consistent with our expectation of the climate change signal propagating into the deeper ocean over time. They also estimate that about half of the extra heat that the ocean now contains, compared with 1865, has been added since 1997 – that is, in roughly the last twenty years as much heat was absorbed as during the preceding 130 years.

“The uncertainties remain large – both in terms of the total ocean heat uptake and its evolution over time. Nevertheless, the increased rate of ocean heat uptake over time is what we’d expect from higher greenhouse gas concentrations.”

Dr Matt Palmer, Climate Scientist at the Met Office Hadley Centre, said:

“This is an important study, largely confirming existing knowledge about human-induced climate change.  The team have compared the available ocean observations to the CMIP5 ensemble, which does a good job of simulating the observed ocean heat content change across three different depth layers.

“This research shows the strengthening of the climate change signal over time and that more of this signal is finding its way into the deep ocean. It highlights the need for more deep-ocean observations to better monitor current and future climate change. It also confirms that ocean heat uptake has been proceeding at the expected rate – the ‘hiatus’ is a surface phenomenon. The Earth is still warming, and the oceans have been taking up the bulk of that heat.”

Prof. Richard Allan, Professor of Climate Science at the University of Reading, said:

“By piecing together the best information from observations and computer simulations this study shows that the oceans are heating up at an increasing rate, an expected consequence of the rising concentrations of greenhouse gases resulting from human activities.”

Prof. John Shepherd, Professorial Research Fellow in Earth System Science at the National Oceanography Centre, University of Southampton, said:

“The ocean takes up an enormous amount of heat, and an increase in the rate of uptake is one reason why the pace of global warming appeared to slow somewhat until last year, but it’s a bit of a mixed blessing. Once the ocean heat uptake settles down again, the rate of warming is likely to return to what it was before. The extra heat will either remain in the ocean, where it may affect both ocean and atmospheric circulation patterns, and so contribute to unusual weather patterns like El Nino, or it may be released to contribute to more rapid or prolonged warming later on. It’s certainly not a cure for climate change, nor any reason to be less concerned about it”.

‘Industrial-era global ocean heat uptake doubles in recent decades’ by Peter J. Gleckler et al. published in Nature Climate Change on Monday 18 January 2016. 

Declared interests

None declared