Pacific Ocean Warming at Fastest Rate in 10,000 Years
Just how rapid is the current rate of warming of the ocean? There is an interesting new article by Rosenthal and collaborators in the latest issue of the journal Science, "Pacific Ocean Heat Content During the Past 10,000 Years" that attempts to address this question. The article compares current rates of ocean warming with long-term paleoclimatic evidence from ocean sediments. So how rapid is the ocean warming? Well, for the Pacific ocean at least, faster than any other time in at least the past 10,000 years.
The study finds, specifically, that (to quote Columbia University's press release) the "middle depths [of the Pacific Ocean] have warmed 15 times faster in the last 60 years than they did during apparent natural warming cycles in the previous 10,000".
Beyond that key overall take-home conclusion, though, there are some enigmatic aspects of the study. The authors argue for substantial differences between proxy reconstructions of surface temperature and their new sediment core evidence of intermediate water temperatures from the tropical IndoPacific, during the past two millenia. The researchers argue that recent warmth is anomalous in the former case, but not the latter. They argue that, while the present rate of ocean warming is unprecedented, the actual level of ocean heat content (which depends not just on surface temperature, but also sub-surface ocean temperatures) is not as high as during Medieval times, i.e. during what they term the "Medieval Warm Period" (this is a somewhat outdated term; the term "Medieval Climate Anomaly" is generally favored by climate scientists because of the regionally variable pattern of surface temperatures changes in past centuries—more on this later).
One complication with their comparison is that the dramatic warming of the past half century is not evident in the various sediment data analyzed in the study. "Modern" conditions conditions are typically defined by the "tops" of the sediment core obtained by drilling down below the ocean bottom. But sediment core tops are notoriously bad estimates of "current" climate conditions because of various factors, including the limited temporal resolution owing to slow sediment deposition rates, and processes that mix and smear information at the top of the core. Core tops for these reasons tend not to record the most recent climate changes. Thus, the researchers' data do not explicitly resolve the large recent increases in temperature (and heat content).
But if the warming of the past half century is not resolved by their data, then the assumption that those data can be registered against a common modern baseline (the authors use a reference period of 1965-1970) too is suspect. That registration is critical to their conclusion that modern heat content has not exceeded the bounds of the past two millennia.
There are also some puzzling inconsistencies between the authors' current conclusions and other previously published evidence implying a very different pattern of global ocean heat content changes over the past two millennia. Current global sea level has been shown to be unprecedented for at least the past two millennia in previous work using both proxy-based sea level reconstructions and predictions from "semi-empirical" models of sea level change.
Thermal expansion due to sub-surface ocean warming is a substantial contributor to the observed rise this century in global sea level. It is thus difficult to reconcile the observation that modern sea level is unprecedented over at least the past two millennia with the authors' claim that there has not been an anomalous increase in global ocean heat content over this time frame. Given that there is unlikely to have been any sea level rise contribution from melting ice sheets prior to the most recent decades, any explanation would have to involve extremely large sea level contributions from the melting of small glaciers and ice caps, contributions that exceed what is actually evident in the climate record.
Finally, we need to maintain a healthy skepticism about broad conclusions about global climate drawn from one specific region like the tropical IndoPacific. It is surprising in this context that the article didn't mention or cite two studies published in the same journal (Science), a few years ago: Mann et al (2009) and Trouet et al (2009) which demonstrate a high degree of regional heterogeneity in global temperature changes over the past millennium. Both studies attribute much of that heterogeneity to dynamical climate responses related to the El Niño phenomenon. The tropical Pacific appears to have been in an anomalous La Niña-like state during the Medieval era. During such a state, which is the flip-side of El Niño, much of the tropical Pacific (the eastern and central tropical Pacific) is unusually cold. But the tropical western Pacific and IndoPacific are especially warm. That makes it perilous to draw inferences about global-scale warmth from this region (see this more detailed discussion at RealClimate).
There a few other minor, odd things about the study. In a figure comparing the sediment records with proxy reconstructions of surface temperature, the authors attribute one of the curves to "Mann 2003" in the figure legend. This would appear to be a reference to a rather old reconstruction by Mann and Jones (2003), which is supplanted by a newer, far more comprehensive study by Mann et al (2008). The authors indeed cite this latter study in footnote of the figure caption. So it is unclear which reconstruction is actually being shown, and the comparison is potentially inappropriate.
The authors, in a different figure, show a recent, longer albeit somewhat more tenuous reconstruction of global temperature over the past 11,000 years by Marcott et al (2013), published in Science earlier this year. That reconstruction was observed to be consistent with that of Mann et al (2008) during the interval of overlap of the past two millennia.
It is also puzzling that the article doesn't show or even cite the most comprehensive hemispheric reconstruction to date, that of the PAGES 2K Consortium published in the journal Nature Geoscience two months before the present paper was submitted to Science. That reconstruction demonstrates modern warming to considerably exceed the peak warmth of the Medieval period, closely resembling the original Mann et al "Hockey Stick." It would have been useful to see all of these reconstructions, each of which demonstrate recent warmth to be anomalous in a long-term context, compared on the same graph against the sediment series of this study.
In summary, the Rosenthal study is interesting and it provides useful new paleoclimate data that give us an incrementally richer understanding of the details of climate changes in pre-historic times. However, there are a number of inconsistencies with other evidence, and debatable assumptions and interpretations, which will require sorting out by the scientific community. That is, of course, the "self-correcting" machinery of science that Carl Sagan spoke so eloquently of.
Visit EcoWatch’s CLIMATE CHANGE page for more related news on this topic.
By Harry Kretchmer
By 2030, almost a third of all the energy consumed in the European Union must come from renewable sources, according to binding targets agreed in 2018. Sweden is helping lead the way.
Sweden is a world leader in renewable energy consumption. Swedish Institute/World Bank
Naturally Warm<p>54% of Sweden's power comes from renewables, and is helped by its geography. With plenty of moving water and 63% forest cover, it's no surprise the <a href="https://sweden.se/nature/energy-use-in-sweden/#" target="_blank">two largest renewable power sources</a> are hydropower and biomass. And that biomass is helping support a local energy boom.</p><p>Heating is a key use of energy in a cold country like Sweden. In recent decades, as fuel oil taxes have increased, the country's power companies have turned to renewables, like biomass, to fuel local 'district heating' plants.</p><p>In Sweden these trace their <a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140#fig3" target="_blank">origins back to 1948</a>, when a power station's excess heat was first used to heat nearby buildings: steam is <a href="https://www.sciencedirect.com/topics/engineering/district-heating-system" target="_blank">forced along a network of pipes</a> to wherever it's needed. Today, there are around 500 district heating systems across the country, from major cities to small villages, providing heat to homes and businesses.</p><p>District heating used to be fueled mainly from the <a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140" target="_blank">by-products of power plants</a>, waste-to-energy plants and industrial processes. These days, however, Sweden is bringing more renewable sources into the mix. And as a result of competition, this localized form of power is now the country's<a href="https://www.sciencedirect.com/science/article/pii/S0360544217304140#fig3" target="_blank" rel="noopener noreferrer"> home-heating market leader.</a></p>
Sweden is using smart grids to turn buildings into energy producers. Huang et al/Elsevier
Energy ‘Prosumers’<p>But Sweden doesn't stop at village-level heating solutions. Its new breed of energy-generation takes hyper-local to the next level.</p><p>One example is in the city of Ludivika where 1970s flats <a href="https://www.buildup.eu/sites/default/files/content/transforming-a-residential-building-cluster-into-electricity-prosumers-in-sweden.pdf" target="_blank">have recently been retrofitted with the latest smart energy technology</a>.</p><p>48 family apartments spread across 3 buildings have been given photovoltaic solar panels, thermal energy storage and heat pump systems. A micro energy grid connects it all, and helps charge electric cars overnight.</p><p>The result is a cluster of 'prosumer' buildings, producing rather than consuming enough power for 77% of residents' needs. With <a href="http://www.diva-portal.org/smash/get/diva2:1232060/FULLTEXT01.pdf" target="_blank" rel="noopener noreferrer">high levels of smart meter usage</a>, it's a model that looks set to spread across Sweden.</p>
<div id="d7bf9" class="rm-shortcode" data-rm-shortcode-id="8757b138d5570bec9d6aad18074a429a"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1273556364263071744" data-partner="rebelmouse"><div style="margin:1em 0">Read more about Western Harbour and book a visit: https://t.co/ujSmVs9rNK 🏡🌳🌊 https://t.co/C5PuPziqIM</div> — Smart City Sweden (@Smart City Sweden)<a href="https://twitter.com/SmartCitySweden/statuses/1273556364263071744">1592474473.0</a></blockquote></div>
Scaling Up<p>A recent development by E.ON in Hyllie, a district on the outskirts of Malmö, southern Sweden, <a href="https://www.eonenergy.com/blog/2019/February/sweden-smart-city" target="_blank">has scaled up the smart grid principle</a>. Energy generation comes from local wind, solar, biomass and waste sources.</p><p>Smart grids then balance the power, react to the weather, deploying extra power when it's colder or putting excess into battery storage when it's warm. The system is not only more efficient, but bills have fallen.</p><p>Smart energy developments like those in Hyllie, Ludivika, and renewable-driven district heating, offer a radical alternative to the centralized energy systems many countries rely on today.</p><p>The EU's leaders have a challenge: how to generate 32% of energy from renewables by 2030. Sweden offers a vision of how technology and local solutions can turn a goal into a reality.</p>
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