Name: Guest post: The threat of high-probability ocean ‘tipping points’
Brand: carbonbrief.org
SKU: carbonbrief-org-15
Availability: OnlineOnly
Rating: 100 (1 reviews)

critic

Guest post: The threat of high-probability ocean ‘tipping points’

preview

Climate change is profoundly altering our oceans and marine ecosystems. Some of these changes are happening quickly and are potentially irreversible. Many are taking place silently and unnoticed.In recent years, – thresholds where a small change could push a system into a completely new state – have increasingly become a focus for the climate research community. However, these are typically thought of in terms of unlikely changes with huge global ramifications – often referred to as “low probability, high impact” events. Examples include the and the rapid .&nbsp;In a new paper, published in the , my co-authors and I instead focus on the potential for what we call “high probability, high impact” tipping points caused by the cumulative impact of warming, acidification and deoxygenation.We present the challenge of dealing with these imminent and long-lasting changes in the Earth system, and discuss options for mitigation and management measures to avoid crossing these tipping points.The ocean is a giant reservoir of heat and . Since the beginning of the industrial revolution, the oceans have taken up of the carbon dioxide (CO2) and added to the atmosphere through human activity.&nbsp;Without ocean uptake, the scale of atmospheric warming would already be much larger. But this comes with a high cost in the form of , – where the alkaline ocean becomes more acidic – and – where the oxygen content of the ocean falls.&nbsp;The potential impact of these processes on the marine environment is . However, in some cases, they could trigger a number of regional tipping points with potentially widespread consequences for marine ecosystems and ocean functioning.Here are some examples:Warming&nbsp;Each species has an optimal temperature range for their physiological functioning. Like humans, most marine organisms are vulnerable to warming above their optimal temperature. Without adaptation, some species will be hit hard by ocean warming. A well-known example is the to tropical coral reef systems, such as Australia’s , to from extreme heat.&nbsp;These coral reef systems play an important role for fisheries, for coastal protection, as fish nurseries, and for a number of other ecosystem services. This serves as an example of how the impact of ocean warming extends far beyond the most sensitive marine organisms, with range shifts being observed across the food web .Deoxygenation&nbsp;Most marine organisms can only exist in seawater with sufficiently high concentrations of dissolved oxygen. Warming of the ocean decreases the solubility of oxygen in the water and slows down ocean mixing, which, in turn, decreases oxygen transport from the surface into the ocean interior.&nbsp;In addition, run-off of nutrients from the land – such as from agriculture and domestic waste – increases the biological productivity in coastal areas, disrupting ecosystems and enhancing deoxygenation. Consequences for marine organisms are huge, with species distribution, growth, survival and ability to reproduce .AcidificationBesides being the , CO2 also changes ocean chemistry, causing the acidification of seawater. Many marine organisms have shells or skeletal structures made of mineral forms particularly vulnerable to ocean acidification. A well-known example are – free-swimming sea snails and sea slugs – that live in the upper 10 metres of the ocean, which are a in the marine food web.&nbsp;Currently observed acidification conditions are already , and are projected to continue and aggravate even with the reduction of carbon emissions to net-zero.While these different processes are individually a danger to marine life, in combination with other threats – such as overfishing, high nutrient input from land and invasive species – they have the potential to cause ecosystem-wide regime shifts.In addition, extreme events – such as or high-acidity, low-oxygen events – lead to severe consequences for marine biodiversity. Across the globe, the observed local and regional changes already add up to a substantial regional – and possibly global – problem. Examples include and anoxic ocean “”.&nbsp;The figure below highlights some of the regions of the world ocean that are under threat from these impacts.While these impacts already need dealing with today, ocean circulation patterns mean that they are also being stored up for the future.The upper ocean mixes on a timescale of decades, while the deep ocean water masses are renewed from the surface on a much longer timescale – from hundreds to thousands of years. The present-day accumulation of heat and carbon are initially largest at the ocean surface. But, through mixing and ocean currents, this excess of heat and carbon is transported away from the surface and into deeper layers.These short and long-term timescales have two consequences. The first is that mixing is not fast enough to prevent the accumulation of heat and carbon in the upper ocean.The second is that deep mixing transports some of the surface excess heat and carbon to greater depths, where long-lasting changes can gradually build up. Consequently, the deep ocean can be altered by climate change irreversibly for thousands of years, even under strong emission reduction scenarios. These impacts are incredibly difficult to monitor at such depths.While the threats to the ocean from are many and varied, there is still time for them to be minimised. We highlight a few action points where scientists are contributing to the development and implementation of mitigation actions.Expert analysis direct to your inbox.Get a round-up of all the important articles and papers selected by Carbon Brief by email. Find out more about our newsletters . By entering your email address you agree for your data to be handled in accordance with our .Your data will be handled in accordance with our .First, scientists are using and observations to determine the regions where the most severe hazards have occurred, are occurring, and may occur in the future. Laboratory and in-situ experiments can help identify vulnerabilities in organisms and ecosystems.Second, progress is being made to define important thresholds in the physiological tolerance of key organisms for changes in temperature, oxygen concentration, nutrient levels and acidity. This also draws attention to the need for metrics of global change that go beyond atmospheric CO2 concentration and global average surface temperature. Keeping a close watch on potential ocean tipping points means tracking ocean temperature changes, acidification, deoxygenation and marine productivity.Third, communication of these threats is improving. While there is still much progress to be made – for example, in building climate and ocean literacy and working with indigenous groups – research into to address global challenges is growing.While headway is being made, much more action is needed. We suggest four system management and societal transformation actions for minimising the likelihood of encountering high-probability, high-impact ocean tipping points:Heinze, C. et al. (2021) The quiet crossing of ocean tipping points, Proceedings of the National Academy of Sciences,This work received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 820989. The contents of this article reflect only the author’s views – the European Commission and their executive agencies are not responsible for any use that may be made of the information it contains.Sharelines from this storyComments4.01.2018Expert analysis direct to your inbox.Get a round-up of all the important articles and papers selected by Carbon Brief by email. Find out more about our newsletters . By entering your email address you agree for your data to be handled in accordance with our .Your data will be handled in accordance with our .

Climate change is profoundly altering our oceans and marine ecosystems. Some of these changes are happening quickly and are potentially irreversible. Many are taking place silently and unnoticed.In recent years, – thresholds where a small change could push a system into a completely new state – have increasingly become a focus for the climate research community. However, these are typically thought of in terms of unlikely changes with huge global ramifications – often referred to as “low probability, high impact” events. Examples include the and the rapid .&nbsp;In a new paper, published in...

Balanced

public

Award-winning journalism focused on #climatechange, science, energy and policy. Sign up to our free newsletters: http://bit.ly/30rx7mw

Guest post: The threat of high-probability ocean ‘tipping points’

No article scores yet.

CRITIC REVIEWS

PUBLIC REVIEWS