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Climate Change Driving Surge in ‘Day-Night Hot Extremes’ in Northern Hemisphere
By Daisy Dunne
Deadly "day-night hot extremes" are increasing across the northern hemisphere due to climate change, a new study finds.
And the number of people exposed to such events, also known as "compound hot extremes," is likely to increase "several-fold" as temperatures continue to climb in the coming decades, the study authors tell Carbon Brief.
If global temperatures reach 2 C — the upper limit set by countries in the Paris agreement — the frequency of compound hot extremes could more than double across the northern hemisphere, when compared to 2012, the research finds.
However, if greenhouse gas emissions are not curbed, compound hot extremes could become eight times more frequent by the end of the century.
The study sets out "clear evidence" that human-caused climate change is leaving its mark on extreme heat events, another scientist tells Carbon Brief.
Day and Night
The new study, published in Nature Communications, looks specifically at "compound hot extremes" — a 24-hour period in summer where hot daytime temperatures are followed by similar nightime temperatures. (Temperatures are considered "hot" if they are in the top 10% of temperatures experienced by a region from 1960-2012.)
These kinds of events pose a particularly high danger to human health, explain study authors Dr Yang Chen, a climate extremes scientist from the Chinese Academy of Meteorological Sciences, and Dr Jun Wang, a climate and meteorological scientist from the Institute of Atmospheric Physics in China. In a joint interview, they tell Carbon Brief:
Simply put, compound hot extremes deprive humans of the valuable chance of relief, which could have been provided by the 'cooling-off' effects of a nighttime low.
Such conditions occurred during the 2003 summer heatwave in Europe, which saw 70,000 deaths across 16 countries, the authors say. Another example is the 1995 Chicago heatwave, which led to more than 700 heat-related deaths in just five days.
The study is the first to present "a complete storyline on compound hot extremes" — investigating how they have changed, the role of climate change in this and how they might increase in the future, the authors say.
The results show that compound hot extremes "are significantly increasing and will continue to increase in frequency and intensity" across the northern hemisphere, say Chen and Wang:
These increases in heat hazards will translate into several-fold increases in population exposure to them. The rise of anthropogenic emission of greenhouse gas emissions is to blame for these increases.
For the first part of their study, the authors analysed the "fingerprint" of human-caused climate change on compound hot extremes to date. To do this, they conducted an "attribution" analysis.
This involves using climate models to produce two sets of simulations: one including all the factors that affect the climate, including human-caused greenhouse gas emissions, volcanic eruptions and solar variability, and one including all of these factors except for greenhouse gas emissions.
The researchers then compared the frequency and intensity of compound hot extremes in both of these scenarios.
They found that only the scenario including human-caused greenhouse gas emissions could closely reproduce the pattern of compound hot extremes observed from 1960 to 2012. In their research paper, the authors write:
We find that the summer-mean warming over 1960-2012 largely dictates the past increases in frequency and intensity of compound hot extremes during that period in both observations and simulations.
The maps below show observed changes in summertime compound hot extreme frequency (left) and intensity (right) across the northern hemisphere from 1960-2012.
The left-hand map shows changes in the number of compound hot extreme days per decade (yellow to red for increases; light to dark blue for decreases), while the right-hand map shows changes in the average temperature of compound hot extremes per decade (same color scale).
Contributions from changing temperature mean and variability. Wang et al. (2020)
The map shows that increases in the frequency and intensity of compound hot extremes are widespread across the northern hemisphere, with parts of continental Europe and China particularly affected.
(Gaps in the data prevented the researchers from analysing changes in the most southern parts of the northern hemisphere, the authors say in their research paper.)
While the global pattern of increases is best explained by human-caused global warming, it is possible that some regional differences may be explained by other factors, the authors say.
For example, the drying of soils could help to explain local variation of heat extremes, the authors say in their research paper.
This is because dry soils accumulate heat during the day and release it at night, Wang and Chen say, making night hot extremes and, therefore, compound hot extremes, more likely.
The authors also used climate models to project possible future changes to compound hot extremes until 2100. They investigated two scenarios: one "intermediate mitigation" pathway with moderately high greenhouse gas emissions ("RCP4.5") and one with very high greenhouse gas emissions ("RCP8.5").
Within each emissions scenario, they also looked at the changes to compound hot extremes expected if the world reaches 1.5 C and 2 C of global warming, which are the temperature limits set by the Paris agreement.
The charts below show the average expected change in the number of summertime compound hot extreme days (purple line), as well as independent hot days (blue line) and independent hot nights (turquoise line) across the northern hemisphere under RCP4.5 (top) and RCP8.5 (bottom) until 2100. (Compound extremes are where a hot day is followed by a hot night, whereas an "independent hot day" is when a hot day is not followed by a hot night.)
On the charts, red circles point out when the temperature limits of 1.5 C and 2 C will be breached in each scenario. The bottom chart also highlights when 4C could be breached. The various data points represent results from different climate models.
(It is worth noting that events are considered to be compound or independent. So, a 24-hour period where a hot day is followed by a hot night would be considered a compound extreme, but not an independent hot day or hot night.)
Constrained projections of summertime hot extremes. Wang et al. (2020)
The results show that the average number of compound hot extreme days across the northern hemisphere in summer would more than double if temperatures reach 2 C, when compared to 2012.
Keeping temperatures at 1.5 C could see five fewer compound hot extreme days across the northern hemisphere, on average, when compared to 2 C, the research adds.
If greenhouse gas emissions are extremely high (RCP8.5), the number of summertime compound hot extremes could increase eight-fold by 2100, when compared to 2012, the results show.
The charts also show that compound hot events are expected to increase at a much more rapid rate than independent hot day or hot night events.
This is chiefly because climate change is known to have a larger effect on nightime temperatures than daytime temperatures, the authors say.
Therefore, as the chances of hot nights become higher, the chances of compound hot events also increase — and, so, the chances of a hot day or night occurring independently decreases, explain Chen and Wang.
The findings reinforce "the urgency in reducing emission of greenhouse gases" for policymakers, say Chen and Wang:
We should keep the point in mind that as the globe warms, future summers are increasingly dominated by compound hot extremes and become more uncomfortable. Namely, a hot day accompanied by a hot night without a relief window for humans might become a 'new norm'. As a result, vigilance against excess heat should be kept through day and night.
I think the main take home message from this study is that we should use consecutive day-night hot extremes as a major heat-health indicator for policymaking, as compound hot extremes are projected to have larger future increases in frequency and intensity then hot days or nights.
The findings produce "clear evidence" that human-caused climate change is leaving its mark on extreme heat events, says Prof Peter Stott, who leads on climate monitoring and attribution at the Met Office Hadley Centre. Stott, who was also not involved in the research, tells Carbon Brief:
I don't find the conclusions of the study very surprising, but I do like the way the authors have comprehensively set out the implications – the clear evidence that the changes to date are driven by human emissions and the clear evidence that future changes will result in significant increases in the frequency and intensity of these compound extremes worldwide.
Reposted with permission from Carbon Brief.
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EcoWatch Daily Newsletter
By Tom Duszynski
The coronavirus is certainly scary, but despite the constant reporting on total cases and a climbing death toll, the reality is that the vast majority of people who come down with COVID-19 survive it. Just as the number of cases grows, so does another number: those who have recovered.
In mid-March, the number of patients in the U.S. who had officially recovered from the virus was close to zero. That number is now in the tens of thousands and is climbing every day. But recovering from COVID-19 is more complicated than simply feeling better. Recovery involves biology, epidemiology and a little bit of bureaucracy too.
How does your body fight off COVID-19?<p>Once a person is exposed the coronavirus, the body starts producing <a href="https://www.mblintl.com/products/what-are-antibodies-mbli/" target="_blank">proteins called antibodies to fight the infection</a>. As these <a href="https://www.statnews.com/2020/03/27/serological-tests-reveal-immune-coronavirus/" target="_blank">antibodies start to successfully contain the virus</a> and keep it from replicating in the body, symptoms usually begin to lessen and you start to feel better. Eventually, if all goes well, your immune system will completely destroy all of the virus in your system. A person who was infected with and survived a virus with no long-term health effects or disabilities has "recovered."</p><p>On average, a person who is infected with SARS-CoV-2 will feel ill for about seven days from the onset of symptoms. Even after symptoms disappear, there still may be small amounts of the virus in a patient's system, and they should stay <a href="https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/steps-when-sick.html" target="_blank">isolated for an additional three days</a> to ensure they have truly <a href="https://health.usnews.com/conditions/articles/coronavirus-recovery-what-to-know" target="_blank">recovered and are no longer infectious</a>.</p>
What about immunity?<p>In general, once you have recovered from a viral infection, your body will keep cells called lymphocytes in your system. These cells "remember" viruses they've previously seen and can react quickly to fight them off again. If you are exposed to a virus you have already had, your antibodies will likely stop the virus before it starts causing symptoms. <a href="https://dx.doi.org/10.5114%2Fceji.2018.77390" target="_blank">You become immune</a>. This is the <a href="https://www.ncbi.nlm.nih.gov/books/NBK27158/" target="_blank">principle behind many vaccines</a>.</p><p>Unfortunately, immunity isn't perfect. For many viruses, like mumps, immunity can wane over time, leaving you <a href="https://www.sciencedaily.com/releases/2016/04/160421145747.htm" target="_blank">susceptible to the virus in the future</a>. This is why you need to get revaccinated – those "booster shots" – occasionally: to prompt your immune system to make more antibodies and memory cells.</p><p>Since this coronavirus is so new, scientists still don't know whether people who recover from COVID-19 are <a href="https://www.cdc.gov/coronavirus/2019-ncov/hcp/faq.html" target="_blank">immune to future infections of the virus</a>. Doctors are finding antibodies in ill and recovered patients, and <a href="https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guidance-management-patients.html" target="_blank">that indicates the development of immunity</a>. But the question remains how long that immunity will last. Other coronaviruses like <a href="https://doi.org/10.1002/jmv.25685" target="_blank">SARS and MERS produce an immune response</a> that will protect a person at least for a short time. I would suspect the same is true of SARS-CoV-2, but the research simply hasn't been done yet to say so definitively.</p>
Why have so few people officially recovered in the US?<p>This is a dangerous virus, so the Centers for Disease Control and Prevention is being extremely careful when deciding what it means to recover from COVID-19. Both medical and testing criteria must be met before a person is <a href="https://www.cdc.gov/coronavirus/2019-ncov/hcp/disposition-in-home-patients.html" target="_blank">officially declared recovered</a>.</p><p>Medically, a person must be fever-free without fever-reducing medications for three consecutive days. They must show an improvement in their other symptoms, including reduced coughing and shortness of breath. And it must be at least seven full days <a href="https://health.usnews.com/conditions/articles/coronavirus-recovery-what-to-know" target="_blank">since the symptoms began</a>.</p><p>In addition to those requirements, the CDC guidelines say that a person must test negative for the coronavirus twice, with the <a href="https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/care-for-someone.html" target="_blank">tests taken at least 24 hours apart</a>.</p><p>Only then, if both the symptom and testing conditions are met, is a person officially considered recovered by the CDC.</p><p>This second testing requirement is likely why there were so few official recovered cases in the U.S. until late March. Initially, there was a <a href="https://www.nytimes.com/2020/03/18/health/coronavirus-test-shortages-face-masks-swabs.html" target="_blank">massive shortage of testing in the U.S.</a> So while many people were certainly recovering over the last few weeks, this could not be officially confirmed. As the country enters the height of the pandemic in the coming weeks, focus is still on <a href="https://www.cdc.gov/coronavirus/2019-nCoV/hcp/clinical-criteria.html" target="_blank">testing those who are infected</a>, not those who have likely recovered.</p><p>Many more people are being tested now that states and private companies have begun <a href="https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/testing-in-us.html" target="_blank">producing and distributing tests</a>. As <a href="https://www.dispatch.com/news/20200406/coronavirus-in-ohio-from-its-rocky-start-testing-for-covid-19-slowly-ramping-up" target="_blank">the number of available tests increases</a> and the pandemic eventually slows in the country, more testing will be available for those who have appeared to recover. As people who have already recovered are tested, the appearance of any new infections will help researchers learn <a href="https://www.statnews.com/2020/03/24/we-need-smart-coronavirus-testing-not-just-more-testing/" target="_blank">how long immunity can be expected to last</a>.</p>
Once a person has recovered, what can they do?<p>Knowing whether or not people are immune to COVID-19 after they recover is going to determine what individuals, communities and society at large can do going forward. If scientists can show that recovered patients are immune to the coronavirus, then a person who has recovered could in theory <a href="https://www.vox.com/2020/3/30/21186822/immunity-to-covid-19-test-coronavirus-rt-pcr-antibody" target="_blank">help support the health care system</a> by caring for those who are infected.</p><p>Once communities pass the peak of the epidemic, the number of new infections will decline, while the number of <a href="https://www.newsweek.com/china-says-passed-peak-coronavirus-epidemic-covid-19-1491863" target="_blank">recovered people will increase</a>. As these trends continue, the risk of transmission will fall. Once the risk of transmission has fallen enough, community-level isolation and social distancing orders will begin to relax and businesses will start to reopen. Based on what other countries have gone through, it will be <a href="https://www.nature.com/articles/d41586-020-00154-w" target="_blank">months until the risk of transmission is low</a> in the U.S.</p><p>But before any of this can happen, the U.S. and the world need to make it through the peak of this pandemic. Social distancing works to slow the spread of infectious diseases and <a href="https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/what-you-can-do.html" target="_blank">is working for COVID-19</a>. Many people will <a href="https://www.yalemedicine.org/stories/2019-novel-coronavirus/" target="_blank">need medical help to recover</a>, and social distancing will slow this virus down and give people the best chance to do so.</p>
By Elizabeth Claire Alberts
The future for the world's oceans often looks grim. Fisheries are set to collapse by 2048, according to one study, and 8 million tons of plastic pollute the ocean every year, causing considerable damage to delicate marine ecosystems. Yet a new study in Nature offers an alternative, and more optimistic view on the ocean's future: it asserts that the entire marine environment could be substantially rebuilt by 2050, if humanity is able to step up to the challenge.
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Across the country, the novel coronavirus is severely affecting black people at much higher rates than whites, according to data released by several states, as The New York Times reported.
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By Zulfikar Abbany
Bread has been a source of basic nutrition for centuries, the holy trinity being wheat, maize and rice. It has also been the reason for a lot of innovation in science and technology, from millstones to microbiological investigations into a family of single-cell fungi called Saccharomyces.
Chemical leavening<p>If you like a little heft in your loaf, you will need a leavening agent.</p><p>For those short on time, you can use baking soda. That's a chemical compound of sodium bicarbonate mixed with potassium bitartrate, or cream of tartar.</p><p>Soda breads have their traditions in parts of eastern and central Europe, and in Ireland and Scotland, with Melrose loaves and "farls."</p><p>They can taste a bit bland, though, and are often considered only as an emergency solution on Sundays. No disrespect intended: They taste just fine fresh from the oven.</p><p>Whether it's chemical or more "natural," leavening relies largely on the production of carbon dioxide.</p><p>When you mix an acid, such as vinegar, buttermilk, yogurt or apple cider, with an alkaline compound like baking soda, you get CO2. That CO2 creates bubbles, which in turn capture steam in the oven and allow a bread to rise.</p><p><span></span>But it's better with yeast. Tastes better, too. It just takes more time. </p>
What is yeast?<p>There are yeasts all around us — on grains, in the air, in biofuels. It even lives inside us, but that's not always a good thing.</p><p><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1090575/pdf/1471-2334-5-22.pdf" target="_blank">Candida yeast</a> can cause infections of the skin, feet, mouth, penis or vagina if it builds up too much in the body.</p><p>One of the most common yeasts, however, is <em>Saccharomyces cerevisiae</em>. That's <a href="https://www.dw.com/en/an-early-beer-archaeologists-tap-ground-at-worlds-oldest-brewery/a-45480731" target="_blank">"brewer's"</a> or "baker's" yeast.</p><p>You can get fresh baker's yeast, often in 42-gram (1.48-ounce) cubes, or as dried yeast (quick action or active, which requires rehydration) in a sachet of 7 grams.</p><p>There's little difference: One is compressed and the other is dehydrated and granulated. But they do the same thing, essentially. </p><p>Some commercial yeast producers add molasses and other nutrients. But natural yeast has plenty of useful nutrients in it anyway, including B group vitamins, so who knows whether it's good or necessary to add them. </p>
How does yeast work?<p>When you mix flour, yeast and water, you set off a veritable chain reaction. Enzymes in the wheat convert starch into sugar. And the yeast creates enzymes of its own to convert those sugars into a form it can absorb.</p><p>The yeast "feeds" on the sugars to create carbon dioxide and alcohol. The yeast burps and farts, releasing gases into the mix, and that creates bubbles to trap CO2. </p><p>It's a vital fermentation process that breaks down the gluten in the flour and helps make your bread more digestible.</p><p>The yeast cells split and reproduce, generating lactic and carbonic acid, raising the temperature and ultimately adding flavor to the mix.</p><p>The longer you leave the yeast to do its thing, the better for your bread. Time is more important than the amount of yeast. </p><p>In fact, that's an enduring question — how much yeast? I'll use 20 grams fresh yeast for 500 grams of flour. Others say that's enough yeast for 1 kilo. If you are converting a dry-yeast recipe to fresh yeast, some bakers advise tripling the weight. So, if a sachet of dried yeast is 7 grams, your fresh yeast is 21 grams.</p><p><span></span>But that also depends on the flours you are using, temperatures in the bowl and the room, and a host of other things. You'll just have to experiment and see. No number of books (and I've read a stack on bread) will help as much as trial and error.</p>
Wild yeast: Sourdough<p>So, good bread needs time. If you have a lot of time, why not move it up a notch and grow wild yeast — a sourdough starter — in your own home?</p><p>A sourdough starter is not to be mistaken (as it often is) for the leaven, or "mother," "sponge," or <em>levain</em>. That's more a second stage, a descendant of the starter. You take a scoop from your starter and add it to another flour and water mixture when you prepare the dough for a new loaf. </p><p>The sourdough process utilizes yeasts naturally present in flour and … yet more time. A longer fermentation process allows a richer lactic acid bacteria <em>lactobacilli</em> or LAB to evolve, and that can be healthy for your gut microbiome.</p><p>It's simple enough to start a sourdough starter. All you need is flour, warm water and time.</p><p>Some suggest equal measures of whole-grain flour and water at 28 degrees Celsius (82 degrees Fahrenheit), some say room temperature — just don't let the water exceed 40 C or the yeasts will die. Some suggest two parts flour to three parts water. But it's up to you whether you want a drier or wetter starter. You will know only through experimentation. </p><p>Some say you should filter tap water to remove chemicals like fluoride and avoid using water that's boiled and then cooled. Others say that really doesn't matter.</p><p>The main thing is, keep it clean and give it time. Days, weeks, months and years.</p>
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