Severe Coral Reef Bleaching Now ‘Five Times More Frequent’ Than 40 Years Ago
By Daisy Dunne
The scale of bleaching has been rising steadily in the last four decades, a study author told Carbon Brief, with the global proportion of coral being hit by bleaching per year rising from 8 percent in the 1980s to 31 percent in 2016.
The findings indicate that "coral reefs as we know them may well vanish in the lifetime of the youngest of us" if no efforts are made to rapidly curb climate change, another scientist told Carbon Brief.
A before and after image of coral bleaching and later dying in March / May 2016, at Lizard Island on the Great Barrier ReefThe Ocean Agency / XL Catlin Seaview Survey / Richard Vevers & Christophe Bailhache
However, these colorful habitats are vulnerable to climate change. High sea temperatures are one of the main causes of coral bleaching, which occurs when stressed corals expel the tiny algae living in their tissues—known as zooxanthellae—leaving behind a stark white skeleton.
The algae provide the corals with energy through photosynthesis. Without them, the corals starve. Although corals can recover from a bleaching event over time, persistent bleaching can kill off entire reefs.
The new study, published in Science, is the first to make a global estimate of how both the frequency and severity of coral reef bleaching have changed over the last 40 years.
It shows that bleaching events have become five times more frequent, with the average reef being affected once every 25 to 30 years in the 1980s and once every six years in 2016.
The findings indicate that coral bleaching is a "modern phenomenon" driven by global warming, said study co-author professor Nick Graham, a Royal Society university research fellow and chair in marine ecology at Lancaster University. He told Carbon Brief:
"All coral reef regions of the world are now experiencing more frequent severe coral bleaching events. Critically, the time between bleaching events is now as short as six years, which is insufficient time for full recovery of coral cover on damaged reefs."
For the study, researchers compiled data on coral bleaching from 1980 to 2016 for 100 coral reefs in 54 countries. The dataset drew from published research as well as direct observations.
For each reef, the researchers recorded "severe bleaching" events—where more than 30 percent of corals were bleached at the scale of tens to hundreds of kilometers—and "moderate bleaching" episodes—where less than 30 percent of corals were affected over the same scale.
They found that, across the globe, the risk of bleaching (both moderate and severe) has increased at a rate of 4 percent per year, with 8 percent of reefs being affected by bleaching per year in the 1980s and 31 percent being affected in 2016.
The researchers also found that the most recent mass bleaching event, from 2015 to 2016, was the most severe on record, affecting 75 percent of the reefs examined in the study.
The map below shows the global extent of coral bleaching in 2015 and 2016, with each circle representing one reef. Red indicates severe bleaching, yellow shows moderate bleaching and blue shows reefs where no substantial bleaching was recorded.
The global extent of coral bleaching from 2015-2016. Each circle represents one of 100 reefs, with red indicating severe bleaching, yellow indicating moderate bleaching and blue showing no bleaching. Hughes et al. (2017)
Whether the impact of coral bleaching is moderate or severe determined by a range of factors, including local sea surface temperature and sea level, as well as nearby human activity, such as pollution.
From 1980 to 2016, the number of bleaching events was highest in the western Atlantic, including central America and the Caribbean, which experienced two to three times more events than other regions such as Australasia, the Indian Ocean and the Pacific Ocean.
The charts below show the percentage of reefs that were affected by moderate (white) and severe (black) coral bleaching events in each of the four regions from 1980 to 2016.
The percentage of coral reefs affected by moderate (white) and severe (black) bleaching from 1980 to 2016 in (A) Australasia, (B) Indian Ocean, ( C) Pacific Ocean, (D) western Atlantic.Hughes et al. (2017)
The research suggests that Australasia and the Middle East have experienced the largest increased risk of coral bleaching over the study period. However, the reason for this is still not clear, Graham said.
Role of Warming
The research shows that climate change is playing an increasingly large role in mass bleaching events, Graham said.
Since 1980, 58 percent of severe bleaching events have been recorded during strong periods of El Niño.
El Niño is a natural phenomenon occurring every five years or so that causes sea surface temperatures to rise in the equatorial Pacific Ocean. As the climate warms, the risk of bleaching during El Niño years is rapidly increasing, said Graham:
"Climate change is causing background sea surface temperatures to rise, such that a smaller and smaller temperature anomaly [rise] is causing corals to become stressed and bleached. El Niño events cause a big temperature anomaly and so, on top of the already warmed seas, the temperatures get far too hot and extensive bleaching occurs."
The remaining 42 percent of events occurred during hot summers in non-El Niño years. These kind of events are also increasing in frequency as the climate continues to warm, Graham said:
"Importantly, other smaller anomalies are now sufficient to cause bleaching, so as climate change continues, coral bleaching events are occurring more and more frequently."
The findings indicate that limiting global warming to 1.5°C above pre-industrial levels, which is the aspirational goal of the Paris agreement, will be "essential" to give coral reefs a chance at survival, Graham said:
"Rapidly reducing carbon emissions is absolutely essential to save this iconic ecosystem that supports a third of all marine biodiversity, provides food security and livelihoods to hundreds of millions of people throughout the tropics and protects thousands of kilometers of coastlines from shoreline erosion."
However, the research shows that even 1.5°C of additional warming could spell disaster for much of the world's coral, said professor Jean-Pierre Gattuso, from the Institute for Sustainable Development and International Relations (IDDRI), who was not involved in the research. He told Carbon Brief:
"The implications of this paper are dreadful: coral reefs as we know them may well vanish in the lifetime of the youngest of us. It is immensely important to make sure that the objectives of the Paris Agreement are met.
"Another implication is that the Paris Agreement will not be enough to save coral reefs. Other solutions must be identified but none, so far, seem to have the required effectiveness and scalability."
In recent months, there have been various plans and techniques proposed to help coral endure climate change, including the use of genetic engineering.
One possible line of action to improve the survival chances of coral could be to remove CO2 from the atmosphere, said study co-author Dr. Mark Eakin, coordinator of the U.S. National Oceanic and Atmospheric Administration's Coral Reef Watch program. This could in theory be achieved through the use of negative emissions technologies, Eakin told Carbon Brief:
"Even 1.5°C warming will cause irreparable harm to coral reefs in many parts of the world. This is why we must redouble our efforts to limit climate change by reducing CO2 levels in the atmosphere, not just reducing emissions."
Reposted with permission from our media associate Carbon Brief.
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By Jeff Berardelli
For the past year, some of the most up-to-date computer models from the world's top climate modeling groups have been "running hot" – projecting that global warming may be even more extreme than earlier thought. Data from some of the model runs has been confounding scientists because it challenges decades of consistent projections.
International Effort to Evaluate Climate Models<p>For the past 25 years the international community has been evaluating and comparing the world's most sophisticated climate models produced by various teams at universities, research centers, and government agencies. The effort is organized by the World Climate Research Programme under the United Nations World Meteorological Organization.</p><p>Climate models are complicated computer programs composed of millions of lines of code that calculate the physical properties and interactions between the main climate forces like the atmosphere, oceans, and solar input. But models also go a lot further, incorporating other systems like ice sheets, forests, and the biosphere, to name a few. The models are then used to simulate the real-world climate system and project how certain changes, like added pollution or land-use changes, will alter the climate.</p><p>Every few years there is a new comprehensive international evaluation called the Coupled Model Intercomparison Project (CMIP). In the sixth such effort, known as CMIP6 and now under way, experts are reviewing about 100 models.</p><p>Information gleaned from this effort will act as a scientific foundation for the U.N.'s Intergovernmental Panel on Climate Change (IPCC) next major assessment report, scheduled for release in 2021. The goal of the report – the sixth in 30 years – is to inform the international community about how much the climate has changed, and, importantly, how much change can be expected in coming decades.</p>
A Conundrum Emerges<p>Over the past year, the CMIP6 collection of models being reviewed threw researchers an unexpected curveball: a significant number of the climate model runs showed substantially more global warming than previous model versions had projected. If accurate, the international climate goals would be nearly impossible to achieve, and there would be significantly more extreme impacts worldwide.</p><p>A foundational experiment in every report addresses "sensitivity": If you double levels of carbon dioxide (CO2) that were in the air before the Industrial Revolution, how much warming do the models show? This doubling is not expected for a few more decades, but it is a quick way to communicate the critical role of greenhouse gases in changing the climate.</p><p>The amount of CO2 in the atmosphere has increased by 35% since the 1800s because of the burning of fossil fuels. As a result, global temperatures have already increased by more than 2 degrees Fahrenheit.</p><p>In the first IPCC assessment report, published in 1990, the answer to that question about the impact of doubling carbon dioxide gave a fairly wide range of results – between 2.7-8 degrees F of global warming. Since then, four more assessments issued six to seven years apart reached nearly the exact same conclusion on sensitivity.</p><p>But that sensitivity may, for the first time, change significantly in next year's assessment. Why? Because starting last year, numerous models in the CMIP6 collection displayed even bigger spikes in temperature upon doubling of CO2 concentrations. We're in serious trouble if the climate sensitivity falls in the mid or upper range of the previous assessments. But if the new, higher estimates are correct, the impacts on civilization would be catastrophic.</p>
In the above CarbonBrief interactive visualization, the bars offer a comparison in the range of sensitivity in the CMIP5 models (gray) and CMIP6 models (blue).
New and Encouraging Evidence Is Emerging<p>At first, scientists were uncertain whether the new model runs were on to something, so the international modeling community dug in to produce multiple studies. The results are not yet conclusive, but a gradual collective sigh of relief seems to be materializing.</p><p>"Evidence is emerging from multiple directions that the models which show the greatest warming in the CMIP6 ensemble are likely too warm," explains Dr. Gavin Schmidt, director of NASA's Goddard Institute for Space Studies.</p><p>For example, <a href="https://www.earth-syst-dynam-discuss.net/esd-2020-23/" target="_blank">a study</a> released April 28 evaluated the past performance of the models making up the CMIP6 ensemble. The team assigned weights to each model based upon historical performance of their warming projections, weighing the poorer performing models less. By doing so, both the mean warming and the range of warming scenarios in the CMIP6 ensemble decreased, meaning the warmest models were the ones with weaker historical performance. This result supports a finding that a subset of the models are too warm.</p><p>That conclusion is supported by another new study evaluating one particular model – the Community Earth System Model (CESM2) – that showed greater warming. Using that model, the researchers simulated the climate in the early Eocene era, about 50 million years ago, when rainforests thrived in the Arctic and Antarctic. The CESM2 simulated a historical climate that seems way too warm compared with what is known about that era from geological data, indicating that the model is likely also too warm in its future projections.</p><p>Two other recent studies of the CMIP6 models being evaluated use clever analysis methods to <a href="https://www.google.com/url?q=https://www.earth-syst-dynam-discuss.net/esd-2019-86/&sa=D&ust=1589209938203000&usg=AFQjCNHYwFB-1KqndGfJ4sXdrrm9DpbLaQ" target="_blank">narrow the range</a> of future warming projections and also <a href="https://www.google.com/url?q=https://advances.sciencemag.org/content/6/12/eaaz9549&sa=D&ust=1589209938203000&usg=AFQjCNEhKY1YZ19qgjSZ_hJM14JmzqXOXw" target="_blank">reduce the projected warming</a> of the CMIP6 models by 10 to 15%.</p><p>Through the intensive research spurred by the CMIP6 climate-sensitivity curveball, scientists have been able to turn a confounding challenge into a confidence builder, providing even greater certainty than they had before in both the abilities of the climate science community and in the computer models used. Moreover, the experience has helped unearth uncertainties remaining in the modeling process.</p><p>Experts conclude much of this uncertainty probably lies in the complexity of clouds. "We have been looking as a community at why the models with greater warming are doing what they are doing – and it's tied to cloud feedbacks in the southern mid-latitudes mostly," explains Schmidt.</p><p>In fact, <a href="https://advances.sciencemag.org/content/6/26/eaba1981" target="_blank">a new study</a> addressing the increased sensitivity was published in Science Advances stating, "Cloud feedbacks and cloud-aerosol interactions are the most likely contributors to the high values and increased range of ECS [sensitivity] in CMIP6."</p>
Understanding the Complexity of Clouds<p>It's long been known in climate modeling circles that cloud processes and interactions are a potential weak link for climate modeling. That reality has been brought front and center by the urgent challenges posed during this CMIP6 evaluation period, but the current evaluation of models also provides an opportunity for discovery and improvement.</p><p>Cloud complexity comes from the reality that clouds have a multitude of sizes, altitudes, and textures. Some clouds cool Earth by providing shade, reflecting sunlight back into space. Others act like a blanket, trapping heat and warming the world.</p><p>Given that about <a href="https://www.nasa.gov/vision/earth/lookingatearth/icesat_light.html" target="_blank">70% of the globe</a> is covered by clouds at any given time, it's no surprise that they play an integral role in regulating the climate. The challenge is to figure out which types of clouds will increase, which will decrease, and what the net effect will be on cooling or warming as the climate changes.</p><p><a href="https://www.nature.com/articles/s41561-019-0310-1" target="_blank">One study</a> last year reached an alarming conclusion: Left unchecked, the release of CO2 into the atmosphere may lead to a tipping point where shallow low clouds disappear – leading to runaway, catastrophic warming of nearly 15 degrees F. While scientists see that outcome as only a remote possibility, it drives home the urgent need to better understand clouds.</p><p>"We have a saying at NOAA: It isn't rocket science – it's much, much harder than that," quips Dr. Chris Fairall, ATOMIC's lead investigator. "One of the major problems for modeling is there is not clean separation of scales." The photo below is one that Fairall took from the NOAA P-3 aircraft.</p>
Investigating the Secrets of Clouds<p>To address the urgent question about the dynamics and role of clouds in a warming world, NOAA and European partners launched their ongoing research effort unprecedented in scale. The U.S. contribution, ATOMIC – short for Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign – is an international science mission that was featured recently on "<a href="https://www.cbsnews.com/video/study-aims-to-examine-links-between-climate-change-and-clouds/" target="_blank">CBS This Morning: Saturday</a>."</p>
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By Melissa Hawkins
After sustained declines in the number of COVID-19 cases over recent months, restrictions are starting to ease across the United States. Numbers of new cases are falling or stable at low numbers in some states, but they are surging in many others. Overall, the U.S. is experiencing a sharp increase in the number of new cases a day, and by late June, had surpassed the peak rate of spread in early April.
Seven day rolling average of number of people confirmed to have COVID-19, per day (not including today). This chart gets updated once per day with data by Johns Hopkins. Johns Hopkins university doesn't provide reliable data for March 12 and March 13. Johns Hopkins CSSE Get the data
To Have a Second Wave, the First Wave Needs to End.<p>A wave of an infection describes a large rise and fall in the number of cases. There isn't a precise epidemiological definition of when a wave begins or ends.</p><p>But with talk of a <a href="https://www.theguardian.com/world/2020/jun/27/new-covid-19-clusters-across-world-spark-fear-of-second-wave" target="_blank">second wave in the news</a>, as an <a href="https://www.american.edu/cas/faculty/mhawkins.cfm" target="_blank">epidemiologist and public health researcher</a>, I think there are two necessary factors that must be met before we can colloquially declare a second wave.</p><p>First, the virus would have to be controlled and transmission brought down to a very low level. That would be the end of the first wave. Then, the virus would need to reappear and result in a large increase in cases and hospitalizations.</p><p>Many countries in <a href="https://doi.org/10.1038/s41562-020-0908-8" target="_blank">Europe and Asia have successfully ended the first wave</a>. <a href="https://www.theguardian.com/world/2020/jun/08/new-zealand-abandons-covid-19-restrictions-after-nation-declared-no-cases" target="_blank">New Zealand</a> and <a href="https://www.newyorker.com/magazine/2020/06/08/how-iceland-beat-the-coronavirus" target="_blank">Iceland</a> have also made it through their first waves and are now essentially coronavirus-free, with very low levels of community transmission and only a handful of active cases currently.</p>
Different States, Different Trends<p>Looking at U.S. numbers as a whole hides what is really going on. Different states are in <a href="https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html" target="_blank">vastly different situations right now</a> and when you look at states individually, four major categories emerge.</p><ol><li>Places where the first wave is ending: States in the Northeast and a few scattered elsewhere experienced large initial spikes but were able to mostly contain the virus and substantially brought down new infections. <a href="https://www.nytimes.com/interactive/2020/us/new-york-coronavirus-cases.html" target="_blank">New York</a> is a good example of this.</li><li>Places still in the first wave: Several states in the South and West – see <a href="https://www.nytimes.com/interactive/2020/us/texas-coronavirus-cases.html" target="_blank">Texas</a> and <a href="https://www.nytimes.com/interactive/2020/us/california-coronavirus-cases.html" target="_blank">California</a> – had some cases early on, but are now seeing massive surges with no sign of slowing down.</li><li>Places in between: Many states were hit early in the first wave, managed to slow it down, but are either at a plateau – like <a href="https://www.nytimes.com/interactive/2020/us/north-dakota-coronavirus-cases.html" target="_blank">North Dakota</a> – or are now seeing steep increases – like <a href="https://www.nytimes.com/interactive/2020/us/oklahoma-coronavirus-cases.html" target="_blank">Oklahoma</a>.</li><li>Places experiencing local second waves: Looking only at a state level, <a href="https://www.nytimes.com/interactive/2020/us/hawaii-coronavirus-cases.html" target="_blank">Hawaii</a>, <a href="https://www.nytimes.com/interactive/2020/us/montana-coronavirus-cases.html" target="_blank">Montana</a> and <a href="https://www.nytimes.com/interactive/2020/us/alaska-coronavirus-cases.html" target="_blank">Alaska</a> could be said to be experiencing second waves. Each state experienced relatively small initial outbreaks and was able to reduce spread to single digits of daily new confirmed cases, but are now all seeing spikes again.</li></ol><p>The trends aren't surprising based on how states have been dealing with reopening. The virus will go wherever there are susceptible people and until the U.S. stops community spread across the entire country, the first wave isn't over.</p>
What Could a Second Wave Look Like?<p>It is possible – though at this point it seems unlikely – that the U.S. could control the virus before a vaccine is developed. If that happens, it would be time to start thinking about a second wave. The question of what it might look like depends in large part on everyone's actions.</p><p>The <a href="https://dx.doi.org/10.1086%2F592454" target="_blank">1918 flu pandemic</a> was characterized by a mild first wave in the winter of 1917-1918 that went away in summer. After restrictions were lifted, people very quickly went back to pre-pandemic life. But a second, deadlier strain came back in fall of 1918 and third in spring of 1919. In total, <a href="https://www.cdc.gov/flu/pandemic-resources/1918-commemoration/1918-pandemic-history.htm" target="_blank">more than 500 million people were infected</a> worldwide and upwards of <a href="https://theconversation.com/compare-the-flu-pandemic-of-1918-and-covid-19-with-caution-the-past-is-not-a-prediction-138895" target="_blank">50 million died</a> over the course of three waves.</p><p>It was the combination of a quick return to normal life and a mutation in the flu's genome that made it more deadly that led to the horrific second and third waves.</p><p>Thankfully, the coronavirus appears to be much more <a href="https://doi.org/10.1016/j.meegid.2020.104351" target="_blank">genetically stable</a> than the influenza virus, and thus less likely to mutate into a more deadly variant. That leaves human behavior as the main risk factor.</p><p>Until a <a href="https://theconversation.com/what-needs-to-go-right-to-get-a-coronavirus-vaccine-in-12-18-months-136816" target="_blank">vaccine or effective treatment is developed</a>, the tried-and-true public health measures of the last months – <a href="https://theconversation.com/this-simple-model-shows-the-importance-of-wearing-masks-and-social-distancing-140423" target="_blank">social distancing,</a> <a href="https://theconversation.com/masks-help-stop-the-spread-of-coronavirus-the-science-is-simple-and-im-one-of-100-experts-urging-governors-to-require-public-mask-wearing-138507" target="_blank">universal mask wearing</a>, frequent hand-washing and avoiding crowded indoor spaces – are the ways to stop the first wave and thwart a second one. And when there are surges like what is happening now in the U.S., further reopening plans need to be put on hold.</p>
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