{"id":292,"date":"2014-09-10T11:39:36","date_gmt":"2014-09-10T11:39:36","guid":{"rendered":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/?p=292"},"modified":"2015-12-21T15:19:38","modified_gmt":"2015-12-21T15:19:38","slug":"ocean-heat-uptake-checking-the-facts","status":"publish","type":"post","link":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/2014\/09\/10\/ocean-heat-uptake-checking-the-facts\/","title":{"rendered":"Ocean heat uptake – checking the facts"},"content":{"rendered":"

The Climate and Environment at Imperial blog has moved. View this post on\u00a0our new\u00a0blog<\/a><\/em>\u00a0<\/em><\/a><\/strong><\/p>\n

By Dr Flora Whitmarsh<\/a>, Grantham Institute<\/a><\/p>\n

The recent slowdown in global temperature<\/a> rise has led to suggestions that global warming has stopped. In fact, the Earth system is still gaining heat, and the slowdown was likely caused by a series of small volcanic eruptions, a downward trend in the solar cycle, and increased heat uptake of the ocean. Writing in the Telegraph,<\/a> Christopher Booker claims that a new paper by Professor Carl Wunsch (Wunsch, 2014)<\/a> shows that ocean warming cannot explain the slowdown because the deeper ocean is in fact cooling rather than warming. Booker is incorrect in his interpretation of the paper, as Professor Wunsch explained in a letter of response to the Telegraph editor <\/a>that was not published. Wunsch also wrote a letter to the editor of The Australian<\/a> following a similarly misleading article in that newspaper. There are two threads to Christopher Booker\u2019s argument in the Telegraph article. First, he suggests that the new paper refutes the idea that the pause is caused by an increase in ocean heat uptake, an interpretation that is untrue. Second, Booker gives a misleading interpretation of Wunsch\u2019s appearance on the 2007 television documentary The Great Global warming Swindle<\/em> in which Wunsch\u2019s views were misrepresented by the documentary makers. Below, I describe the significance of ocean heat uptake and then discuss Booker\u2019s two points in turn.<\/p>\n

\"Figure<\/a>
Figure 1: the amount of heat taken up by the upper ocean (above 700 m), deep ocean (below 700 m), atmosphere and earth, and the amount going into melting ice (IPCC, 2013<\/a>).<\/figcaption><\/figure>\n

\u00a0\u00a0\u00a0The significance of ocean heat uptake<\/h4>\n

The ocean is an important heat sink and has taken up over 90% of the extra heat absorbed by the Earth system over the last century. There is natural variation in the amount of heat being taken up by the ocean. This is part of the reason why the observed increase in surface temperatures has not been uniform in the past. All studies including this latest one agree that the ocean above 2000 m is absorbing a significant amount of heat and this is the main focus of studies trying to detect and attribute global warming. The study of the ocean below 2000m is interesting from a scientific point of view but is less relevant to the study of climate change because it takes a very long time for heat to mix to these lower layers. Heat is transferred to the deep ocean by the movement of water masses \u2013 the mixing driven by the small-scale movement of water molecules is too slow to be of much significance. Due to the locations of the major ocean currents, parts of the deep ocean such as the western Atlantic and the Southern Ocean in the Antarctic have been in contact with the surface relatively recently, meaning they would be expected to have warmed due to global warming. By contrast, much of the Pacific Ocean below 1500 m has not been in contact with the surface for around a thousand years \u2013 something that has been demonstrated by studying the radioactive decay of carbon-14 atoms \u00a0in a technique similar to the carbon dating of objects (Matsumoto, 2007<\/a> \u2013 see figure 2).<\/p>\n

\"Figure<\/a>
Figure 2: The circulation carbon-14 age of ocean water below 1500 m (Matsumoto, 2007). Much of the water in the deep Pacific Ocean has not been in contact with the surface for around 1000 years, meaning that its temperature is unlikely to have been influenced by human activities since the industrial revolution.<\/figcaption><\/figure>\n

\u00a0 \u00a0 \u00a0 \u00a0What is happening in the deep ocean?<\/h4>\n

Christopher Booker writes, \u201cProf Carl Wunsch \u2026 has produced a paper suggesting not only that the warmists have no real evidence to support their claim other than computer modelling, but that the deeper levels of the oceans have, if anything, not been warming but cooling recently, thanks to climate changes dating back centuries.\u201d<\/p>\n

\"Figure<\/a>
Figure 3: Change in ocean heat content between 1993 and 2011 below 2000 m depth, in units of 108 Joules. There has been heating at this level in the Western Atlantic and Southern Ocean and cooling elsewhere.<\/figcaption><\/figure>\n

In the paper under discussion, Bidecadal Thermal Changes in the Abyssal Ocean<\/a>, Wunsch looks at observations of ocean heat content. He found that the ocean as a whole and the top 700 m had gained heat since 1993, but that there had been an overall decline in heat content below 2000 m according to the available data. There has been a warming in the regions of the deep ocean below 2000 m where it would be expected due to the transport of water from the surface to the abyss by major ocean currents, i.e. the western Atlantic Ocean and the Southern Ocean (see figure 3). There was an observed cooling below 2000 m in other parts of the ocean including most of the Pacific. Much of the deep Pacific Ocean would not be expected to have warmed due to climate change because the water has not been in recent contact with the surface (figure 2). The available observations are very sparse and only about a third of the water below 2000 m was sampled at all during the period under discussion, meaning it is not known whether these results reflect a genuine cooling below 2000 m. Because there was heating in some places and cooling in others, it is particularly hard to accurately determine the mean from very sparse observations. The main conclusion of Wunsch, 2014 was in fact that more observations are needed to improve our understanding of processes involved in transporting water to the deep ocean. This is a subject which has received relatively little attention, with much more research effort being concentrated on the upper ocean. It is likely that this is partially due to the difficulty involved in observing the ocean at depth, and partly because the upper ocean is of interest due to its direct impact on weather patterns, for example through its role in the formation of El Ni\u00f1o<\/a> and La Ni\u00f1a<\/a> conditions. None of this changes the fact that the Earth system as whole is gaining heat, and that a significant proportion of that heat is being taken up by the ocean, mostly in the top 700 m. The paper doesn\u2019t significantly change our understanding of the pause in surface temperature rise. We know that natural processes do change the amount of heat taken up by the ocean over time, and that surface temperature rise has not been uniform in the past. However, precisely quantifying how much heat has been taken up by the deep ocean is still not possible with current observations.<\/p>\n

\n

 <\/p>\n

\u00a0 \u00a0 \u00a0 The Great Global Warming Swindle<\/h4>\n

Referring to the 2007 television documentary, The Great Global Warming Swindle<\/em>, Booker suggested that Wunsch had privately held \u201csceptic\u201d views at the time the programme was aired, but didn\u2019t feel able to express these views in public, \u201cSo anxious is the professor not to be seen as a \u201cclimate sceptic\u201d that, [after being interviewed for] The Great Global Warming Swindle<\/em>, he complained to Ofcom that, although he had said all those things he was shown as saying, he hadn\u2019t been told that the programme would be dedicated to explaining the scientific case against global warming.\u201d Professor Wunsch\u2019s views on The Great Global Warming Swindle<\/em> are explained at length on his professional webpage<\/a> in an article dated March 2007. I will not paraphrase his comments in detail, but suffice it to say he states his belief that \u201cclimate change is real, a major threat, and almost surely has a major human-induced component\u201d, and wrote to the documentary makers to say, \u201cI am the one who was swindled\u201d because they misrepresented his views by quoting him out of context. In an update written three months later,<\/a> Wunsch made it clear that he did not complain to Ofcom under duress from other scientists. In fact, he felt so strongly that his opinions had been misrepresented that he filed his complaint despite threats by the documentary maker to sue him for libel. References<\/strong> Matsumoto, K. (2007), Radiocarbon-based circulation age of the world oceans, J. Geophys. Res., 112, C09004. Wunsch, 2014: Carl Wunsch and Patrick Heimbach, 2014: Bidecadal Thermal Changes in the Abyssal Ocean.\u00a0J. Phys. Oceanogr.<\/em>,\u00a044<\/strong>, 2013\u20132030.<\/p>\n","protected":false},"excerpt":{"rendered":"

The Climate and Environment at Imperial blog has moved. View this post on\u00a0our new\u00a0blog\u00a0 By Dr Flora Whitmarsh, Grantham Institute The recent slowdown in global temperature rise has led to suggestions that global warming has stopped. In fact, the Earth system is still gaining heat, and the slowdown was likely caused by a series of […]<\/p>\n","protected":false},"author":741,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17115,17114,17131,8855],"tags":[],"class_list":["post-292","post","type-post","status-publish","format-standard","hentry","category-climate-scepticism","category-communicating-climate-change","category-earth-systems","category-media"],"_links":{"self":[{"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/posts\/292","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/users\/741"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/comments?post=292"}],"version-history":[{"count":17,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/posts\/292\/revisions"}],"predecessor-version":[{"id":723,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/posts\/292\/revisions\/723"}],"wp:attachment":[{"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/media?parent=292"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/categories?post=292"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs-staging.imperial.ac.uk\/climate-at-imperial\/wp-json\/wp\/v2\/tags?post=292"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}