Earth Had Its Second Warmest Year in Recorded History in 2019

Earth had its second warmest year on record in 2019, just 0.04°C behind 2016, said NOAA and NASA on January 15. Global ocean temperatures and global land temperatures were both the second warmest on record. Global satellite-measured temperatures in 2019 for the lowest 8 km of the atmosphere were the third warmest or second warmest in the 42-year record, according to the University of Alabama Huntsville (UAH) and RSS, respectively.

By continent, here are the 2019 temperature rankings:

Australia (and Oceania): warmest year on record

Europe: 2nd warmest

South America: 2nd warmest

Asia: 3rd warmest

Africa: 3rd warmest

North America: 14th warmest

Depature of temperature from average
Figure 1. Departure of temperature from average for 2019, the second warmest year the globe has seen since record keeping began in 1880, according to NOAA and NASA. Record high annual temperatures over land surfaces were measured across parts of central Europe, Asia, Australia, southern Africa, Madagascar, New Zealand, North America, and eastern South America. Record high sea surface temperatures were observed across parts of all oceans, specifically, parts of the North and South Atlantic Ocean, the western Indian Ocean, and areas of northern, central and southwestern Pacific Ocean. No land or ocean areas had record-cold temperatures in 2019. Credit: NOAA National Centers for Environmental Information (NCEI)

In the U.S., 2019 was the 34th warmest year on record, going back to 1895, but the year was the warmest on record for Alaska, North Carolina, and Georgia. As detailed in a January 8 post by Weather Underground’s Bob Henson, 2019 was the 2nd wettest year in U.S. history. Marathon, Florida, located about halfway between Key Largo and Key West, recorded an annual average temperature in 2019 of 81.7°F (27.6°C). “This beats by a very big margin every yearly temperature ever recorded in any of the 50 U.S. states,” said weather records expert Maximiliano Herrera.                                                                        

The remarkable global warmth of 2019 means that the six warmest years on record since 1880 were the last six years—2014 through 2019. The near-record global warmth in 2019 is all the more remarkable since it occurred during the minimum of the weakest solar cycle in 100+ years, and during a year without a strong El Niño (though a weak El Niño was present in the first half of 2019, ending in July). Record-warm global temperatures typically occur during strong El Niño events, and when the solar cycle is near its maximum. The near-record warmth of 2019 is thus a testament to how greatly human-caused global warming is impacting the planet.

Ocean Heat Content
Figure 2. Upper 2000 m ocean heat content from 1955 through 2019. The histogram represents annual departure from average (units: ZJ), wherein positive anomalies relative to a 1981−2010 baseline are shown as red bars and negative anomalies as blue. The two black dashed lines are the linear trends over 1955–86 and 1987−2019, respectively. Credit: Cheng, L., and Coauthors, 2020: Record-setting ocean warmth continued in 2019. Adv. Atmos. Sci., 37(2), 137−142,

Warmest year on record for total ocean heat content

The total heat content of the world’s oceans (OHC) in 2019 was the warmest in recorded human history, according to a January 13 paper by Cheng et al., Record-Setting Ocean Warmth Continued in 2019,  published in Advances in Atmospheric Sciences. In the uppermost 2000 meters of the oceans, there were 228 Zetta Joules more heat in 2019 than the 1981−2010 average; 2019 had 25 Zetta Joules more OHC than 2018 (a Zetta Joule is one sextillion Joules– ten to the 21st power). “We found that 2019 was not only the warmest year on record, it displayed the largest single-year increase of the entire decade, a sobering reminder that human-caused heating of our planet continues unabated,” said Penn State’s Dr. Michael Mann, one of the co-authors. The gain in ocean heat between 2018 and 2019 was about 44 times as great as all the energy used by humans in one year.

More than 90% of the increasing heat from human-caused global warming accumulates in the ocean because of its large heat capacity. The remaining heating manifests as atmospheric warming, a drying and warming landmass, and melting of land and sea ice. The past ten years are the ten warmest years on record for total ocean heat content. Increasing OHC causes sea level rise through thermal expansion of the water and melting of glaciers in contact with the ocean, and contributes to “marine heat waves” that kill coral reefs and disrupt atmospheric circulation patterns.

A remarkable slew of high temperature records

International records researcher Maximiliano Herrera keeps the pulse of the planet in remarkable detail, and he logged 22 nations or territories that set or tied their all-time heat records in 2019, tying it with 2016 for most such records. No nations or territories set or tied an all-time cold record in 2019. Among the global weather stations with a long period of record of at least 40 years, Herrera documented 632 that set (not tied) their all-time heat record; six of these stations did so twice in 2019, for a total of 638 exceedances of an all-time heat record. Just 11 stations with a long-term period of record set an all-time cold record in 2019.

Mr. Herrera’s computed the 2019 average temperature for each station by summing up and averaging daily temperatures, and came up with this list of the top five stations with the highest yearly average temperatures for 2019:

1: Matam, Senegal: 31.7°C (89.1°F)
2: Makkah Arafat, Saudi Arabia: 31.6°C (88.9°F)
3: Yelimane, Mali: 31.2°C (88.2°F)
3: Gizan, Saudi Arabia: 31.2°C (88.2°F)
5: Djibouti Ambouli, Djibouti:  31.1°C (88.0°F)

Here are the all-time records for highest yearly average:

1: Makkah, Saudi Arabia: 32.9°C (91.2°F)  2010, 2016
2: Nema, Mauritania: 32.8°C (91.0°F)  2010
3: Yelimane, Mali: 32.6°C (90.7°F)  2010
4: Hombori, Mali: 32.3°C (90.2°F)  2010
5: Kiffa, Mauritania: 32.2°C (90.0°F) 2010
5: Menaka, Mali: 32.2°C (90.0°F)  2010

Notable global heat and cold marks for 2019

Hottest temperature in the Northern Hemisphere: 53.1°C (127.6°F) at Shahdad, Iran, 2 July

Coldest temperature in the Northern Hemisphere: -60.5°C (-76.9°F) at GEOsummit, Greenland, 14 January

Hottest temperature in the Southern Hemisphere: 49.9°C (121.8°F) at Nullarbor, Australia, 19 December

Coldest temperature in the Southern Hemisphere: -82.7°C (-116.9°F) at Dome A, Antarctica, 15 June

(Courtesy of Maximiliano Herrera)

Twenty-two all-time national/territorial heat records set or tied in 2019

All-time high temperature records were tied or broken in 22 of the world’s nations and territories in 2019, tying it with 2016 for most prolific year on record for all-time national heat records, according to international records researcher Maximiliano Herrera; 2017 holds third place with 14 heat records. Here are 2019’s national heat records, with notations by Herrera at the end:

Christmas Island (Australia): 31.6°C (88.9°F), 19 January

Reunion Islands (France): 37.0°C (98.6°F), 25 January

Angola: 41.6°C (106.9°F), 22 March

Togo: 43.5°C (110.3°F), 28 March (later tied on 4 April)

Vietnam: 43.4°C, (110.1°F), 20 April

Jamaica: 39.1°C (102.4°F) at Shortwood Teacher’s College, 22 June

France: 46.0°C (114.8°F) at Verargues, 28 June

Andorra: 39.4°C (102.9°F) at Borda Vidal, 28 June

Cuba: 39.1°C (102.4°F) at Veguitas (Cuba), 30 June

Jersey (crown dependency of Britain): 36.0°C (96.8°F) at Jersey Airport, 23 July (record tied)

Belgium41.8°C (107.2°F) at Begijnendijk, 25 July

Germany: 41.2°C (108.7°F) at Tonisvorst and Duisburg, 25 July*

Luxembourg: 40.8°C (105.4°F) at Steinsel, 25 July

Netherlands: 40.7°C (105.3°F) at Gilze Rijen, 25 July

United Kingdom: 38.7°C (101.7°F) at Cambridge, 25 July

Aland Islands: 31.6°C (88.9°F) at Jomala, 27 July

Norway: 35.6°C (96.1°F) at Laksfors, 27 July (record tied)**

Syria: 50.0°C (122.0°F) at Hasakah, 13 August***

Wake Island (United States Minor Outlying Islands): 36.6°C (97.9°F) at Wake Airfield, 15 August

Guadeloupe (French territory): 36.6°C (97.9°F) at Vieux Habitants, 9 September

Zimbabwe: 45.9°C (114.6°F) at Buffalo Range, 28 October

Comoros: 36.0°C (96.8°F) at Hahaya Airport, 23 November (record tied)

* The official national record of 42.6°C measured the same day at Lingen is irregular and totally incompatible with nearby stations data and with the atmospheric conditions. The station has a history of overexposure and of being unreliable and is set to be moved. Despite this, the record was made official by the German DWD. Estimated overexposure is estimated to be about 2°C.

** This tied record was dismissed by the Norwegian Met. Service on weak grounds despite being reliable and compatible with nearby stations data and the atmospheric conditions. Confoundingly, the totally unreliable and irregular records set in August 1901—30 years before the installment of the first reliable temperature shelter with a Stevenson Screen in Oslo—have not been dismissed.

*** The Hasakah, Syria station has 1°C precision. The max temperature of 50.0°C is supported by nearby stations, so the record can be accepted.

No all-time national cold records were set in 2019. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Jérôme Reynaud also tracks all-time and monthly national extreme temperature records at (in French language).

One hundred thirty-four additional monthly national/territorial heat records beaten or tied in 2019

In addition to the 22 all-time any-month heat records listed above, 134 national monthly records were also beaten or tied in 2019. If we add together these totals, there were 156 monthly national/territorial heat records beaten or tied in 2019; one monthly cold record was set (in August in Svalbard). Here are the monthly all-time national heat records for 2019:

January (5): Micronesia, Paraguay, Angola, Equatorial Guinea, Palau
February (19): Chile, Marshall Islands, Guyana, United Kingdom, Denmark, Sweden, Netherlands, Belgium, Luxembourg, Andorra, Austria, Hungary, Jersey, Guernsey, Slovakia, San Marino, Slovenia, Angola, Papua New Guinea
March (5): Australia, Marshall Islands, India, Kenya, Northern Marianas
April (7): Angola, Togo, French Southern Territories, Mayotte, Taiwan, Kenya, Mauritius
May (12): Kenya, Indonesia, Niger, French Southern Territories, Syria, Tonga, Laos, Vietnam, Japan, Israel, Cyprus, Turkey
June (16): India, Tonga, Namibia, Lithuania, Senegal, Qatar, Chile, Laos, Vietnam, Germany, Czech Republic, Poland, Switzerland, Luxembourg, Liechtenstein, St. Barthelemy
July (10): Iran, Wallis and Futuna, Namibia, Jordan, Israel, Hong Kong, Chile, Bonaire, Mauritius, Guadeloupe
August (5): Taiwan, Cape Verde, Namibia, Wallis and Futuna, Kenya
September (13): Oman, Brunei, Niger, Saba, Nicaragua, Paraguay, Brazil, Solomon Islands, Morocco, Comoros, Laos, Jamaica, Kenya
October (16): Hong Kong, Mongolia, Morocco, Micronesia, Qatar, Kuwait, North Korea, China, Saba, Thailand, Mozambique, Botswana, Malawi, Falkland Islands, South Georgia and Sandwich Islands, French Southern Territories
November (12): St Pierre et Miquelon, Haiti, Syria, Tuvalu, Antigua and Barbuda, Reunion Island, South Africa, Namibia, Thailand, Liberia, Singapore, Mexico
December (14): Indonesia, Iceland, Australia, Cuba, India, Chile, Liberia, Guinea Bissau, Saba, UK, Mexico, Fiji, French Southern Territories, Mayotte

(Courtesy of Maximiliano Herrera)

Hemispheric and continental temperature records in 2019

Highest minimum temperature ever recorded in the Southern Hemisphere: 35.9°C (96.6°F) at Noona, Australia, 18 January. The record was beaten again on 26 January, with a minimum temperature of 36.6°C (97.9°F) recorded at Borrona Downs, Australia. This is also the highest minimum temperature on record for the globe for the month of January.

Highest temperature ever recorded in March globally: 48.5°C (91.4°F) at Emu Creek, Australia, on 11 March.

Highest temperature ever recorded in Asia in March: 46.9°C (116.4°F) at Kapde, India, 25 March. The data comes from a state (not central government) station, and may not be officially recognized, but is supported by data from several nearby stations.

Highest minimum temperature ever recorded in June in the Southern Hemisphere: 28.9°C (84.0°F) at Funafuti, Tuvalu on 15 June.

Highest minimum temperature ever recorded in August in the Southern Hemisphere (tie): 28.2°C (82.8°F) at Funafuti, Tuvalu on 15 August.

Highest temperature ever recorded in October in the Northern Hemisphere: 47.6°C (117.7°F) at Al Wafra, Kuwait on 3 October.

– Highest minimum temperature ever recorded in October globally: 33.0°C (91.4°F) at Sedom, Israel on 15 October.

Highest temperature ever recorded in Africa in November: 47.5°C (117.5°F) at Vioolsdrif, South Africa on 27 November (starting from 28 November, the station started giving incorrect temperatures, but the Nov 27th record was fully confirmed by an almost identical temperature at the Noordower station, a few miles from Vioolsdrif).

Highest temperature ever recorded in December globally: 49.9°C (121.8°F) at Nullarbor, Australia on 19 December

Highest minimum temperature ever recorded in December globally: 36.0°C (96.8°F) at Wallungurry, Australia on 26 December

Departure of temperature from average
Figure 3. Departure of temperature from average for December 2019, the second warmest December for the globe since record keeping began in 1880, according to NOAA and NASA. Record-warm December temperatures were observed across most of Australia and across parts of the Indian Ocean, Africa, Europe, the Atlantic Ocean, and the northern and western Pacific Ocean. No land or ocean areas had record-cold December temperatures. Credit: NOAA National Centers for Environmental Information (NCEI)

December 2019: Earth’s Second Warmest December on Record

December 2019 was the planet’s second warmest December since record keeping began in 1880, said NOAA’s National Centers for Environmental Information (NCEI) on January 15. NASA also rated December 2019 as the second warmest December on record, a scant 0.05°C behind the record-setting December 2015, when a strong El Niño event was in progress.

Global ocean temperatures during December 2019 were the second warmest on record, according to NOAA, as were global land temperatures. Global satellite-measured temperatures in December 2019 for the lowest 8 km of the atmosphere were the warmest in the 42-year record, according to the University of Alabama Huntsville (UAH) and RSS.

Neutral El Niño conditions reign

NOAA’s January 9 monthly discussion of the state of the El Niño/Southern Oscillation (ENSO) stated that neutral ENSO conditions existed, with neither an El Niño nor a La Niña event in progress. Over the past month, sea surface temperatures (SSTs) in the benchmark Niño3.4 region of the eastern tropical Pacific were near the 0.5°C above-average threshold need to be considered El Niño conditions, though. A strong westerly wind burst (WWB) near the Dateline was in progress this week, which will help keep the ocean close to the El Niño threshold. Most climate models predict that sea surface temperatures in the Niño3.4 region will stay near the El Niño threshold into March before decreasing to near-average levels by late spring.

Forecasters at NOAA and the International Research Institute for Climate and Society (IRI) are calling for a roughly 60% chance of neutral conditions continuing through the Northern Hemisphere spring, and a 50% chance of neutral conditions continuing through the summer of 2020. They put the odds of an El Niño event forming by spring at about 30%; the odds of a La Niña event were less than 10%. For the August-September-October peak portion of hurricane season, the odds of El Niño and La Niña being given were roughly equal, between 25 – 30%.

Departure of Temperature From Average
Figure 4. Departure of sea surface temperatures (SSTs) in the benchmark Niño 3.4 region (in the equatorial Pacific) ending on January 15, 2020. Over the past month, SSTs were 0.1 – 0.5°C above average, falling short of the 0.5°C above-average threshold need to be considered El Niño conditions. Credit: Levi Cowan

December Arctic sea ice extent: fifth lowest on record

According to the National Snow and Ice Data Center (NSIDC), Arctic sea ice extent during December was the fifth lowest in the 41-year satellite record. By the end of December, daily sea ice extent was the seventh lowest on record, and the highest since December 2014.

In Antarctica, sea ice extent in December 2019 was also the fifth lowest for December since satellite records began in 1979.

Notable global heat and cold marks for December 2019

Hottest temperature in the Northern Hemisphere: 40.4°C (104.7°F) at Tambacounda, Senegal, 1 December

Coldest temperature in the Northern Hemisphere: -56.7°C (-70.1°F) at GEOSummit, Greenland, 10 December

Hottest temperature in the Southern Hemisphere: 49.9°C (121.8°F) at Nullarbor, Australia, 19 December

Coldest temperature in the Southern Hemisphere: -43.2°C (-45.8°F) at Dome A, Antarctica, 2 December

(Courtesy of Maximiliano Herrera)

Major weather stations that set (not tied) all-time heat or cold records in December 2019

Among global stations with a period of record of at least 40 years, 31 set new all-time heat records in December. There were no stations that set all-time cold records.

Kowanyama (Australia) max.  41.9°C, 3 December

Eucla (Australia) max. 49.8°C, 19 December

Ceduna (Australia) max. 48.9°C, 19 December

Hawker (Australia) max. 46.1°C, 19 December
Coober Pedy (Australia) max. 48.3°C, 20 December

Keith (Australia) max. 47.8°C, 20 December

Lameroo (Australia) max. 48.4°C, 20 December

Mount Gambier (Australia) max. 45.9°C, 20 December

Coonawarra (Australia) max. 45.8°C, 20 December

Naracoorte (Australia) max. 47.7°C, 20 December

Padthaway (Australia) max. 46.1°C, 20 December

Cape Nelson (Australia) max. 45.1°C, 20 December

Loxton (Australia) max. 47.3°C, 20 December

Renmark (Australia) max. 48.6°C,20 December

Cape Otway (Australia) max. 43.4°C, 20 December

Portland Airport (Australia) max. 43.6°C, 20 December

Hamilton (Australia) max. 45.0°C, 20 December

Nowra (Australia) max. 45.6°C, 21 December

Goulburn Aiport (Australia) max. 42.1°C, 21 December

Young (Australia) max. 44.1°C, 21 December

Sandy Cape (Australia) max. 36.0°C, 22 December
Glen Innes (Australia) max. 37.3°C, 22 December 

Rapel (Chile) max. 38.4°C, 23 December
Juan de Nova Island (French Southern Territories, France) max. 35.4°C, 24 December
Giles (Australia) max. 46.8°C, 25 December
Alice Springs (Australia) max. 45.7°C, 25 December
Rabbit Flat (Australia) max. 47.9°C, 25 December
Daly Waters (Australia) max. 45.6°C, 27 December
Bage (Brazil) max. 41.1°C, 28 December
Sao Gabriel (Brazil) max. 41.2°C, 28 December
Hobart Airport (Australia) max. 40.8°C, 30 December

(Courtesy of Maximiliano Herrera)

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Watch the first ever video of a chemical bond breaking and forming

metal bonds

Chemical bonding is one of chemistry’s most fundamental concepts

Toshiyuki Shirai/EyeEm/Getty Images

A chemical bond between two metal atoms has been filmed breaking and forming for the first time – something scientists say they only dreamed of seeingA chemical bond between two atoms has been recorded breaking and forming for the first time. Watching this happen in real time “was absolutely unbelievable”, says Andrei Khlobystov at the University of Nottingham, UK, who led the team that recorded it happening.

“We were very excited,” says Khlobystov. “We knew exactly what was happening because we recognised this as a chemical process straight away, …

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Evidence Shows Whooping Cough Is Evolving Into a ‘Superbug’, Scientists Warn

It starts off like an ordinary cold, but it doesn’t end like one. Whooping cough, aka the ‘100-day cough’, is a highly contagious bacterial disease that infects millions of people around the world, killing tens of thousands every year.


Fortunately, vaccines to protect us from the Bordetella pertussis bacterium that causes whooping cough have been around since the mid-20th century, shielding people from the intense, sometimes fatal respiratory symptoms. Unfortunately, B. pertussis is not standing still.

In new world-first research, a team of Australian scientists has discovered how B. pertussis strains are adapting to the current acellular vaccine (ACV) used in Australia, which is similar to the ACVs used for whooping cough in other countries around the world.

“We found the whooping cough strains were evolving to improve their survival, regardless of whether a person was vaccinated or not,” explains microbiologist Laurence Luu from UNSW.

“Put simply, the bacteria that cause whooping cough are becoming better at hiding and better at feeding – they’re morphing into a superbug.”

According to the findings, which used a technique called ‘surface shaving’ to analyse proteins that envelop B. pertussis at the cellular level, the strains studied were seen to be producing more nutrient-binding proteins and transport proteins, but fewer immunogenic proteins, when compared to previous research on the bacterium.


The researchers say these new changes in B. pertussis mean that the bacteria may be “metabolically fitter” than previous generations, and can more efficiently scavenge nutrients from hosts, while avoiding the host’s immune system responses.

In addition, because the evolved forms might not trigger immune responses as much, it’s possible people could be carrying an infection without realising, since fewer symptoms would show.

“The bacteria might still colonise you and survive without causing the disease,” says Luu.

“You probably wouldn’t know you’ve been infected with the whooping cough bacteria because you don’t get the symptoms.”

The new study builds upon multiple findings made by UNSW researchers in recent years, including the discovery that B. pertussis strains in China were evolving through selection pressure, and that strains without a surface protein called pertactin (targeted by whooping cough vaccines) could have an evolutionary advantage.

It all sounds pretty scary, and the latest research on superbugs in general indicates they’re already responsible for sickening 3 million people in the US every year, some 35,000 of which don’t survive the infection.

In terms of whooping cough though, the UNSW team says there’s no need to panic. B. pertussis is not yet a superbug, and current immunisation medicines still work – but the researchers do emphasise that new vaccines should be developed in the next five to 10 years, to counter the seeming changes underway in B. pertussis.

“Right now the vaccines are still very effective against the current strains,” Luu told The Sydney Morning Herald.

“In the future we do need a new vaccine to combat these strains as they continue to evolve.”

The findings are reported in Vaccine.


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What Is a Gamma-Ray Burst?

Gamma-ray bursts are the strongest and brightest explosions in the universe, thought to be generated during the formation of black holes. Though they last mere seconds, gamma-ray bursts produce as much energy as the sun will emit during its entire 10-billion-year existence. 

The enigmatic phenomena were first seen in 1967 by a U.S. Air Force satellite called Vela. The probe was designed to keep watch for secret Soviet nuclear testing, but it ended up spotting dazzling gamma-rays — the most powerful electromagnetic radiation — coming from beyond the solar system, according to NASA. When such an event happened, it would briefly become the brightest gamma-ray object in the observable universe.

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Do Carbon Offsets Really Work? It Depends on the Details

Last week, JetBlue announced it will offset its 15 billion to 17 billion pounds of greenhouse gas emissions by purchasing carbon credits and pumping cleaner-burning aviation fuel into planes landing at San Francisco International Airport. Great! Or is it? American corporations across the economy are trying to build up their green credentials, and carbon offsets seem to be the hammer of choice.

Investment and university pension funds, cement manufacturers, home heating distributors, tech giants like Google and Amazon, and the ride-hailing firm Lyft all say they are reducing their carbon footprint through similar offsets. Yet some critics worry the programs are an excuse to not take tougher measures to curb climate change. If not done right, the purchase of offsets can act as a marketing campaign that ends up providing cover for companies’ climate-harming practices.

When a company buys offsets, it helps fund projects elsewhere to help reduce greenhouse gas emissions, such as planting trees in Indonesia or installing giant machines inside California dairies that suck up the methane produced by burping and farting cows and turn it into a usable biofuel. What offsets don’t do is force their buyer to change any of its operations.

Supporters of offsets say they are only an acceptable tool once companies have done everything they can to pollute less, such as tightening up manufacturing processes, cutting down on office heating, or making delivery trucks run on cleaner fuels. Purchasing carbon offsets “is clearly better than doing nothing,” says Cameron Hepburn, who directs Oxford University’s economics of sustainability program. They can also help finance emerging green practices, technologies, and services that otherwise might struggle to find customers. “We know we will have to remove a lot of carbon dioxide from the atmosphere, and offsets are helpful in priming that market,” Hepburn says. But he and others caution that carbon offsets still need third-party verification to make sure they do what they are supposed to do, and that the specific carbon-reducing action wouldn’t have been taken otherwise.

That’s where it gets messy, says Barbara Haya, a research fellow at UC Berkeley, where she studies the effectiveness of carbon offset programs. “What would JetBlue have done if they couldn’t buy offsets?” Haya says. “Would they have put money into efficiency of the planes, or invested in future biofuels to create a long-term alternative to fossil fuels? That’s the fundamental question we have to ask for voluntary offsets: How much is it taking the place of real long-term solutions?”

Haya points to JetBlue’s investment in sustainable aviation fuel as a big plus, unlike some airlines that only buy the offset and continue with business as usual. Haya is helping the University of California’s 10 campuses become carbon neutral by 2025. To reach that goal, the university system will have to both cut back on energy use and purchase offsets. Because solar and wind power are now price-competitive with fossil fuel-generated electricity in California, using those renewable sources of energy is good for the planet and helps the university reduce its emissions, but it won’t qualify as a carbon offset, Haya says.

Instead, the big push in California now is for forest regeneration (namely, planting more trees) and changing farming practices. Disney, ConocoPhillips, and Poseidon Resources bought $6.7 million worth of offsets to restore and replant a 100-acre parcel of a state park in the mountains west of San Diego. In 2018, the latest year for which data is available, such nature-based solutions accounted for a reduction of 100 million metric tons of CO2 globally, according to a recent report by the nonprofit group Forest Trends. That reflects about $300 million in purchased offsets.

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Scientists Are Probing How Ginkgo Trees Stay Youthful for Hundreds of Years

A single Ginkgo biloba tree might drop its distinct fan-shaped leaves every year for centuries, if not millennia. For perspective, one that’s about 1,300 years old — nearing the upper limits of documented ginkgo lifespan — first sprouted when the Byzantine empire was still young

And as ginkgo age, they don’t just survive — they thrive. Though 600-year-old ginkgos grow thinner annual rings, they’re likely to pump out just as much defensive and immune-supporting chemicals as their younger relatives, according to new research published in the Proceedings of the National Academy of Sciences

Young at 300

From this data, it appears that Ginkgo biloba, native to China, don’t have a predetermined lifespan. Unlike annuals that die off every year, “there’s no end point in their ability to keep growing,” says Rick Dixon, a biochemist at the University of North Texas and co-author of the paper.

Not only do individual ginkgos grow old, the entire species is prehistoric; some fossilized leaves date to 200 million years ago. Understanding aging in these long-lived, ancient species is difficult, however. Study co-author Jinxing Lin of the Beijing Forestry University was already deploying genome-sequencing technology to decode the ginkgo longevity techniques before Dixon entered the project.

The team focused on the cambium, or the surface layer that grows each year, creating trees’ annual rings. DNA sequences and genome analysis from nine ginkgos — with ages around 20, 200 or 600 years old — showed that genes responsible for thickening each layer were less active in the older trees.

But other signs of aging didn’t appear. Most plants eventually reach senescence — or, as Dixon puts it, a period of “gradually croaking.” Genes responsible for that life phase weren’t any more active in the oldest ginkgo specimen.

Ginkgos, like other trees, produce antioxidants and antimicrobials to stay healthy, too — redwoods have such a high concentration of the latter, the molecules give the species its distinct hue, Dixon says. The various genes needed to produce those compounds appeared to be just as active in the old ginkgo trees as they were in the young ones, as were genes related to the ginkgo immune system.

With a strong immune system and no sign of senescence, “there’s no programmed mechanism for death that we could ascertain from [this] study,” Dixon says.

Secrets to a Long Life

As for how ginkgos have dodged clear signs of decay, Dixon says it’s not clear. If stressed or sick, many types of trees will devote more of their energy stores to immune defense instead of growth, he says. But it’s unclear if ginkgos reallocate resources that way.

Dixon does think it’s possible similar mechanisms are at work in other long-lived species, such as redwoods (which have an average lifespan of 800 to 1,500 years) and English yew (which aren’t considered “old” until they’re 900 or so.)

Dixon points out that they didn’t measure actual levels of antioxidants or immunity boosters in the trees — just the genes indicating their presence. Also, the team only studied the cambium for signs of aging. The root system probably deserves some attention too, Dixon says.

Next up, the team might see if Ginkgo biloba DNA, like our own genetic code, gains mutations as the tree ages. But, who knows: The tree might have a way to prevent that, too.

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How to restore the legendary acoustics of Notre Dame after the fire

For centuries, the interior
of Notre Dame never saw much sunlight. But when Brian Katz stepped inside the
cathedral last July, the place was drenched in light, its famous arched ceiling
open to the sky. Nearly three months before, on April 15, 2019, a fire had
ripped through the Paris cathedral. Now, charred wood lay heaped on the floor,
mingled with toxic lead dust. The acrid scent of fire lingered. But Katz and
his colleague Mylène Pardoen had one main concern: the sound.

fundamental to Notre Dame’s voice was missing: its reverberance, that echolike
quality that the grandest cathedrals are known for. “You didn’t hear the
building anymore,” Katz says.

the fire, the tap of a heel or a cough would hang in the air for many seconds,
a feature that imbued visitors with a tendency to step softly and keep voices
low. Notre Dame de Paris — which translates as “Our Lady of Paris” — had a way
of imposing silence upon her guests. To Katz and Pardoen, the cathedral’s
personality had been erased.

there was reason for hope. Much of the cathedral remained relatively untouched
by the fire; wooden chairs still stood neatly in rows, and paintings and
sculptures — though covered in dust — remained intact.

repairs had already begun. Damaged pillars and flying buttresses were
reinforced, and nets hung high in the arches to catch falling debris. Robotic
devices swept up rubble in places too dangerous for humans to set foot.

Notre Dame de Paris interior
Last year’s disastrous blaze in the Paris cathedral has put heritage acoustics in the spotlight as researchers work to restore the building’s reverberant splendor. Duy Phuong Nguyen/Alamy Stock Photo

architects, builders and historians begin the process of rebuilding Notre Dame,
Katz — an acoustics researcher at CNRS, the Centre National de la Recherche
Scientifique, and Sorbonne University in Paris — is on a mission to help
restore the building’s sonic signature.

work has been happening at other historical places, too. The disaster at Notre
Dame has put a field known as heritage acoustics in the spotlight. Science has
made it possible to document the acoustics and re-create the symphonic grandeur
of destroyed or altered structures. Researchers are wielding their knowledge of
physics to unveil a hidden history of sound in historical buildings. 

past was not a silent place,” says acoustician Damian Murphy of the University
of York in England. “Sound is a fundamental part of our human experience.”

Notre Dame, Katz and colleagues had a fortuitous head start. Using a computer
simulation and acoustic measurements the group made in the intact cathedral in
2013, the researchers had already digitally reproduced the building’s
reverberance. Katz is using that work to predict how choices made during the
reconstruction might alter Notre Dame’s effect on the ears.

can also resurrect the acoustics of Notre Dame of old, showing the impact of
renovations from previous eras in the medieval cathedral’s past, focusing on
how the building would have responded to the sounds within. Meanwhile Pardoen,
of CNRS and the Maisons des Sciences de l’Homme in Lyon, aims to re-create
those long-ago sounds. 

Mylène Pardoen and Brian Katz
Mylène Pardoen and Brian Katz (left to right) study the sounds of historical environments and buildings, and are helping with Notre Dame’s recovery. Here, the two visit the Abbey of Saint-Germain-des-Prés, another Paris church where Katz has done acoustics research.E. Conover

is a transient, ethereal phenomenon, and it tends to be neglected in historical
records. While photographs and drawings can preserve the visual impact of a
building or scene, documenting the sonic impact of a space is more complicated.
But for many people, sound provides an intimate part of the sensation, the je
ne sais quoi of being in a particular place. Eyes closed, you can still tell
immediately whether a room is tiny or soaring and grand.

Aural history

Cathedrals are a classic study subject for heritage acoustics. But sonic scrutiny has been applied to other spaces, including other religious buildings, theaters and even prehistoric caves (SN Online: 7/6/17; 6/26/17). Murphy, for instance, has studied the acoustics of a beloved chocolate factory and an underground nuclear reactor cavern.

cathedrals in particular, “the sound and the feeling you get when you are
inside … is key for the character” of the buildings, says acoustic engineer
Lidia Álvarez-Morales of the University of York. She and colleagues recently
measured the acoustics of four English cathedrals, including York Minster. That
Gothic structure is larger than Notre Dame and suffered a catastrophic fire in
1984. The cathedral was later restored.

The acoustics within a room are all about how the sound reflects off the surfaces inside. When you clap your hands, for example, vibrations of air molecules travel in a wave, causing variations in pressure. Some of those waves travel directly to your ear, which registers an immediate sound. But others travel in all directions until they reach a surface such as a wall, floor or object within the room. Sound waves can bounce off that surface and reach your ear at a later time (SN: 7/13/13, p. 10).

a place with a single reflecting surface, such as the distant wall of a canyon,
the reflected waves produce an echo, a delayed repetition of the original
sound. But in a cathedral, reverberation is the rule. “Reverberation happens
when we have, say, a thousand reflections that are all coming back to us so
fast that we can’t resolve any individual one of them with our auditory
system,” says acoustician Braxton Boren of American University in Washington,
D.C. As a result, the sound is drawn out, slowly trailing off to silence over
several seconds.

Materials that tend to reflect sound waves and enhance reverberation, such as marble and limestone, are common in cathedrals. In contrast, a more typical room has surfaces — carpets, drapes and even the people within the room — that mostly absorb sound waves (SN: 11/15/03, p. 308). Larger rooms also boost sound’s staying power, as the waves take longer to travel between surfaces. Before the fire, with its arched limestone ceiling reaching 33 meters high and a 4,800-square-meter marble floor, Notre Dame was like a giant, mirrored fun house for sound, bouncing the waves around and around.

reverberation time of a room is the number of seconds it takes for an initial,
loud sound to become so quiet that it can no longer be heard. Specifically,
it’s an estimate of how long it takes a sound to fade by 60 decibels. While a
typical living room might have a reverberation time of half a second, and a
concert hall might reverberate for two seconds, cathedrals can have
reverberation times in excess of five seconds. 

long reverberation times, fast-moving music or speech can be muddied, with
notes and words stepping on top of one another. Gothic cathedrals were designed
to be grand spaces — their long reverberation may have been a by-product. But
music evolved to fit the space: For organ music or religious chanting, “the
acoustic conditions are really good, because this kind of music has been
designed for those buildings,” Álvarez-Morales says.

fact, Notre Dame’s special sound may have inspired the birth of polyphonic
music — in which different voices sing separate notes, instead of the same
pitch — in the 12th and 13th centuries. The Gregorian chants sung in the
cathedral in medieval times were monophonic, featuring only one note at a time.
But the drawn-out acoustics meant that consecutive notes tended to overlap.

acousticians believe this effect may have provided a chance to experiment with
which notes sounded good together, eventually developing into voices singing in
harmony. This practice is now so common it seems obvious. But at the time, it
was revolutionary. As a result, the roots of modern Western music may have been
shaped by the acoustics of Notre Dame. “It’s incredibly historically
significant,” Boren says.

Sound of silence

On the day of the fire,
Parisians gathered to watch the dramatic blaze. When Katz first heard the news,
he didn’t quite believe it. Like so many others, he decided he had to see for

the throngs, Paris was mostly silent, Katz says. “No one was really talking
above a whisper. To have that many people staring in awe was really strange.”
Katz opens his eyes wide while remembering the scene. “No one knew what to say
or what to do, but we were all standing there.”

The next day, Katz realized there was something he could do. The 2013 data his group had taken were the only detailed measurements of the acoustics of Notre Dame. He also had his computer simulation of the cathedral. Such acoustic models include the locations of the various surfaces within a room along with estimates of how well each material would absorb sound. And despite the destruction of the cathedral’s roof and medieval timbers, talk of restoring the wounded edifice had already started.

the cathedral, Katz had measured a property known as “room impulse response,”
which captures how the sound levels within a room vary over time after a brief
initial noise. From that impulse response, researchers can derive the reverberation
time and subtle characteristics that can affect how a listener perceives a
room. One such property is the length of the delay between when the first sound
waves reach a listener and the arrival of the second, reflected set of sound

Notre Dame fire damage
In July, three months after the fire, Mylène Pardoen (shown, left), Brian Katz and others wore protective suits and breathing masks inside Notre Dame. Fallen masonry and charred timbers littered the cathedral’s floor.Both: B. Katz and M. Pardoen/CNRS

these measurements of the cathedral, Katz had calibrated his computer model,
which allowed him to accurately reproduce Notre Dame’s lost acoustics. And now
he could tell architects what they needed to do to ensure the building would
maintain its acoustic splendor.

exudes a nearly constant air of bemusement, as if he can’t fully grasp the
cosmic circumstances that led him to become the foremost expert on Notre Dame’s
acoustics. With a graying beard and long wavy hair tied back in a loose knot,
his look is halfway between musician and physicist. But neither category quite
fits: He doesn’t play any instruments, and he’s not a conventional physicist.

a child, Katz’s attempts at learning musical instruments fizzled: He abandoned
both the cello and the saxophone. While studying physics at Brandeis University
in Waltham, Mass., Katz diverged from his college classmates, who were
fascinated with astrophysics or subatomic particles. “That wasn’t really my
thing,” Katz says: He stuck to the human scale.

Katz stumbled into acoustics thanks to his experience setting up sound systems
for events at Brandeis. With a Ph.D. from Penn State, he eventually became an
acoustics researcher in Paris. But he’s no audio-gear geek either. He declares
that his home audio system is “crap.”

Music from ruins

The acoustic properties of
damaged or demolished buildings have been resurrected before. Murphy and
colleagues re-created the 16th century sound of a ruined church called St.
Mary’s Abbey, founded in 1088 in York. Today, only remnants of the abbey’s
walls endure — arched windows frame sky and trees within a city park. But
Murphy and colleagues pieced together the architecture of the lost church as
best they could, consulting with archaeologists and studying historical
references. By putting that information into a computer simulation, the group
got a sense of how the space would reverberate.

2015, singers performed a concert within the ruins, with the original reverberation
of the abbey applied to their voices in real time. Audience members seated
within the church’s footprint heard what the music would have sounded like in
the intact space.

Only ruins remain of St. Mary’s Abbey in York, England. But Damian Murphy and colleagues built a computer simulation to restore the acoustic grandeur of the 16th century church. A recording made in an echo-free room begins the piece. The acoustics of another cathedral, York Minster in England, are applied after 8 seconds, and the music becomes more reverberant. At around 22 seconds, the acoustics is changed to match that reconstructed for the ruined abbey.

an acoustic time machine, such techniques can also help researchers understand
how the acoustics of still-intact buildings might have differed in the past, as
a result of either renovations or differences in how the church was used or
decorated, and how that would have altered the music played within them. “For
anyone who’s fallen in love with music from another era, we can’t really
re-create it without re-creating the acoustic conditions,” Boren says. 

example, in the 16th century Church of the Redentore in Venice, Italy, music
was composed for a special festival held each July, when citizens packed the
church. All those people could have had a big impact on the sound: Humans “are
actually one of the most absorbent surfaces,” Boren says.

festival still takes place today, but the church uses speakers to amplify the
music, which drastically changes the acoustics, Boren says. He wanted to
understand how the church sounded during festivals of the past.

and colleagues produced an auralization of the church, the acoustic equivalent
of a visualization. The researchers took a musical recording from a space with
very little reverberation and applied the acoustics from their simulation of
the church — both with and without the crowd.

Redentore simulation
In this simulation of the acoustics of the Church of the Redentore in Venice, sound waves bounce off the various surfaces in the building. Colors indicate how many times the waves have reflected. The time in milliseconds is indicated in the bottom right corner.Braxton Boren/American Univ.

involved a process called convolution, which changes how long various
frequencies hang in the air. The musical recording was broken up into tiny
slices in time, and each slice was multiplied by the room’s impulse response.
Summing up all those slices produced the final sound.

measurements had revealed that the empty church had a reverberation time of
seven seconds. But in Boren and colleagues’ simulation, reverberation time was
cut in half when the church was filled with people and decked out with festive

the church was full, sounds didn’t ring out as long, so the notes came through
more clearly. In the past, when composers wrote music for the Venice landmark,
they may have taken the room’s reverberation time into account, including the
effects of the crowd.

work was made easier by the fact that the building the team was studying is
intact, and the researchers had measurements from within. Whereas Murphy’s team
had to use a fair bit of guesswork to simulate the ruined St. Mary’s Abbey,
Boren’s group used its data to ensure the simulation faithfully re-created the
building’s sound. The same goes for Katz’s Notre Dame simulation, which is why
his prefire measurements are so crucial.

incredibly lucky that Brian [Katz] was able to get into that space and take all
the measurements that he did,” Boren says. “Those are going to be very critical
for actually isolating what the acoustics of Notre Dame were like before.”

The measure of a cathedral

On April 24, 2013, six
years before the fire and 850 years after Notre Dame’s first stone was laid,
Katz and colleagues arrived at the cathedral lugging microphones and other
equipment. Late that night, after a concert had ended and the last of the
musicians and concertgoers had spilled out into the spring evening, Katz and
his team got to work.

stood like silent sentinels in the centuries-old aisles. Orange and black
cables threaded through walkways. A laptop rested on a chair — a seat normally
occupied by the faithful now reserved for technology. And a dummy of a human
head outfitted with microphones in its ears perched on a post, its blank face
surveying the ornate surroundings.

Sound recording setup
Brian Katz took detailed acoustic measurements in Notre Dame in 2013, using microphones on stands and a dummy head. These benchmark data will help reveal how rebuilding could alter the cathedral’s sound.B. Katz/CNRS

precisely pin down Notre Dame’s room impulse response, Katz’s group played a
sound called a sine sweep, which starts on a low note and slides gradually up
to a higher pitch. It’s designed to test the full range of pitches that humans
can hear, because different pitches can reverberate for different lengths of

measured the cathedral’s response to the sine sweep. That response varies based
on where in a room the sound is coming from, and where the microphone is. So
the researchers moved the speaker and microphones from place to place,
repeating the measurements. Using that data, Katz calculated that Notre Dame’s
reverberation time was around six seconds on average — more than 10 times as
long as a typical living room’s. The reverberation time varied depending on the
pitch; for a note of middle C, the reverberation lasted eight seconds.

Tuning up

Next, Katz and colleagues
turned to the computer simulation, comparing the simulated reverberation with
the reverberation they measured in the cathedral. The results were close, but
didn’t quite match for all frequencies of sound. That’s to be expected: Notre
Dame’s walls might be a little better or worse at absorbing sound than a
typical limestone wall, for example. So Katz and colleagues tweaked the amount
of absorption of various surfaces until the acoustic properties of the
simulated cathedral aligned with reality.

researchers then made an auralization of Notre Dame, using audio from the
concert that took place in Notre Dame the night that Katz made his
measurements. That concert, a performance of “La Vierge,” composed by Jules
Massenet in the late 19th century, was recorded with microphones positioned
very close to the performers. The mics picked up mostly direct sound rather
than the cathedral’s reverberation. Katz used his computer model to re-create
how the concert would have sounded for a listener wandering through other parts
of the church.

Next, Katz and colleagues added visuals to that audio to make a virtual reality re-creation of the performance, which they  call “Ghost Orchestra.” They reported the work at the European Acoustics Association’s EuroRegio conference in 2016. Wearing a virtual-reality headset, the viewer flies about the simulated cathedral as the music plays, swooping low over the orchestra. In the far reaches of the building, the individual notes are more muddied. Turn your head, and as your ears move positions, the sound changes too. Since the fire, Katz and colleagues have been working on improvements to the video.

A virtual reality simulation of a concert in Notre Dame, a work-in-progress by Brian Katz and colleagues, re-creates the acoustics of the church. In this clip from the 360-degree video, the sound changes as the viewer moves around the cathedral.

Brian Katz and David Poirier-Quinot/CNRS, Sorbonne University

forward, Katz plans to tweak his model to account for the design and materials
to be used in the proposed cathedral refurbishments. Even relatively minor
choices — such as whether to carpet some of the aisles — could create a
noticeable difference. Katz also aims to adjust his model to understand how
Notre Dame may have sounded in the past, cataloging its progression through a
series of changes. Some of the past renovations could have altered the
cathedral’s acoustics, even cosmetic changes like coatings of paint and the
hanging of tapestries or artwork.

building stands for 850-plus years without damage, refurbishments and aesthetic
tweaks. Once Notre Dame’s construction began in 1163, it continued off and on
for almost 200 years, until the middle of the 14th century. In 1699, King Louis
XIV started a round of updates, including a new marble altar, with statues of
himself and his father flanking the Virgin Mary holding Jesus’ dead body.

the French Revolution, statues were beheaded, and the church was used as a
warehouse, falling into disrepair. Victor Hugo’s novel The Hunchback of
Notre Dame
was published in 1831 and may have inspired Parisians to give the
cathedral some TLC. Beginning in 1845, renovations led by architect
Eugène-Emmanuel Viollet-le-Duc shored up the crumbling structure and added the
cathedral’s spire (destroyed by the 2019 fire), among other changes. The fire
is believed to have broken out accidentally during restoration work.

Crafting a soundscape

One thing Katz can’t do is
reproduce the actual sounds that might have been present in those earlier eras.
That’s the specialty of Pardoen, Katz’s companion on the July visit to the
damaged Notre Dame. Calling herself a “soundscape archaeologist,” Pardoen pieces
together the sounds of past environments: battlefields, cathedrals and cities.

close-cropped gray hair and dark clothes, Pardoen seems no-nonsense. But
chatting with Katz over coffee, she breaks the veneer of seriousness by
frequently interrupting the conversation to mimic the noises she studies, like
the “choo click choo click” of a loom or the “crrrrrr” of stone cutters.

magnum opus is a video soundscape of central Paris during the second half of
the 18th century, when Paris streets bustled with people, and bridges were crammed
with buildings several stories high. In the video, the viewer wanders the city
streets, taking in the sounds: the clacking of horse hooves, washerwomen working
at the banks of the Seine, leatherworkers engaged in their craft and even the
buzzing of flies around the fish market.

Mylène Pardoen recreated the soundscape of 18th century Paris, using historical documents and maps. Pardoen records her sounds as accurately as possible, using replicas of artisans’ tools of the time, for example.

Projet Bretez/CNRS

cultivate this sonic bouquet, Pardoen consulted maps, historical documents and
paintings. She found replicas of the tools that would have been common at the
time and recorded them in use to collect historically accurate sounds.

Pardoen plans to exhume the forgotten sounds of Notre Dame. Rather than
re-creating religious ceremonies or concerts, she’ll focus on the everyday noises.
In earlier times, artisans and merchants crowded the neighborhood around the
cathedral, and the resulting cacophony leaked into the church’s interior. By
filtering these sounds through Katz’s acoustic model, Pardoen and Katz aim to
achieve the ambience of Notre Dame at various periods of its history.

As the cleanup progresses, Katz and Pardoen will return regularly to monitor the acoustics of the damaged building. The two are part of a group — Association des Scientifiques au Service de la Restauration de Notre-Dame de Paris, the Association of Scientists in the Service of the Restoration of Notre Dame of Paris — that aims to consolidate scientific expertise to better understand the cathedral and assist in its reconstruction. 

will have to decide which version of the cathedral to aim for, the Notre Dame
that existed just before the fire, a version from an earlier era or something
new and different. Giving architects, politicians and the public a chance to
explore the sonic history of Notre Dame could help inform decisions about its

“No historic building is ever completely static,” says Murphy, of the University of York. “This terrible fire, which is a considerable tragedy, is just the next stage in the life of Notre Dame.”

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Once More, With Turning – Scientific American Blog Network

On our latest episode of our podcast My Favorite Theorem, my cohost Kevin Knudson and I talked with University of Arkansas mathematician and artist Edmund Harriss. I was lucky enough to be in the studio with him because we were both part of the Illustrating Mathematics semester program at the Institute for Computational and Experimental Research in Mathematics (ICERM) last fall.

You can listen to the episode here or at, where there is also a transcript.

Harriss chose to talk about the Gauss-Bonnet theorem, which relates the topology of a two-dimensional surface to its geometry. The total curvature of a surface—how much it bends and in what directions—is related to a few large-scale properties (topology): whether it is orientable and how many holes it has.

With this episode, the Gauss-Bonnet theorem makes its second appearance on My Favorite Theorem. Our guest Jeanne Clelland picked for her episode almost two years ago. This is the third time we’ve had a repeated theorem, and something I love about our guests and the show is that even when the underlying mathematics is the same, different people talk about their theorems completely differently, and the episodes usually end up having very different flavors.

To overgeneralize a bit, our former guest Clelland took a bird’s-eye view of the theorem and the surfaces to which it applies, and Harriss talked about the theorem in terms of the “turning” (also known as holonomy if you want to be fancy) around loops on the surface and about what it means for real, physical objects in the world. Both are great ways to view and appreciate a wonderful theorem!

Harriss’s point of view fits perfectly into one of his recent artistic/making endeavors, Curvahedra. These are construction toys that you can use to make different surfaces. Harriss has used them to help kids explore the mathematics of surfaces and discover versions of the Gauss-Bonnet theorem for themselves. You can connect the pieces in different ways that give different geometries and topologies to the resulting surfaces.

In each episode of the podcast, we invite our guest to pair their theorem with something. While donuts are a classic pairing for anything topology-related, Harris went a little more sophisticated with a pear-walnut salad. Get all the details on the episode, ideally while eating a fancy salad.

You can find Harriss on Twitter and his blog. With Alex Bellos, he has put together two mathematics-themed coloring books. Learn more about Curvahedra here.

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Area of Amazon affected by wildfires predicted to grow by 2050

Members of the IBAMA forest fire brigade (named Prevfogo) fight burning in the Amazon area of rural settlement PDS Nova Fronteira, in the city of Novo Progresso, Para state, northern Brazil, this Tuesday, September 3rd. Since the end of August Prevfogo has been acting with the assistance of Brazilian Army military. Bolsonaro government budget cuts since January 2019 have severely affected brigades, which have been reduced in critical regions such as the Amazon. (Photo by Gustavo Basso/NurPhoto via Getty Images)

Amazon deforestation officially hit its highest level in a decade in November

Gustavo Basso/NurPhoto via Getty Images

Amazon wildfires are predicted to worsen, doubling the amount of an important region of forest affected by 2050. The result could be to convert the Amazon from a carbon sink into a net source of carbon dioxide emissions.

Paulo Brando at the University of California, Irvine and his colleagues developed a model to predict how climate change and deforestation in the southern Brazilian Amazon, a wildfire hotspot, are likely to influence wildfires and their associated greenhouse gas emissions.

The model predicts a doubling in the area burned by wildfires from approximately 3.4 million hectares across the 2000s to about 6.8 million hectares in the 2040s, in the worst case scenario of deforestation and rapid climate change. By 2050, the total area burned is predicted to reach 23 million hectares – 16 per cent of the existing forests in that part of Brazil.


“We have to reduce deforestation to tackle the biggest problem,” says Brando. In Brazil, 100 per cent of wildfires are started by people, often as part of agricultural practices, he says. “We can do better than we are doing right now.”

“Unlike Australia where bushfires can propagate, in the Amazon they only propagate to a few hundred metres because the forest is very wet,” says Carlos Nobre at the University of São Paulo in Brazil, who wasn’t involved in the study. But it is getting hotter and drier due to climate change and other factors, which means the Amazon is likely to become more vulnerable to spreading wildfires in future, says Nobre.

The Amazon removes between one and two billion tonnes of carbon dioxide from the atmosphere each year, equivalent to 2.5 to 5 per cent of global emissions. If wildfires increase, eventually the total emissions resulting from fire will exceed 2 billion tonnes, turning the Amazon into a net carbon source.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aay1632

More on these topics:

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New Observations From Hubble Could Confirm a Leading Theory on Dark Matter

A new technique using the Hubble Space Telescope and a feature of general relativity has revealed the smallest clumps of dark matter ever identified – up to 100,000 times less massive than the Milky Way galaxy’s dark matter halo.


And these (relatively) teeny tiny clumps of dark matter nicely agree with one of the leading dark matter theories – what astronomers call cold dark matter.

“We made a very compelling observational test for the cold dark matter model and it passes with flying colours,” said astrophysicist Tommaso Treu of the University of California, Los Angeles.

We don’t actually know what dark matter is. We can’t directly detect it. What we do know is that the Universe doesn’t behave entirely as it should if we apply our current physics to what we can directly observe. Stars on the outer edges of galaxies, for example, move faster than they should, as though under the influence of some invisible mass.

We call this mass “dark matter,” and there are several hypotheses as to how it works. Among them are hot dark matter – where “hot” means “particles moving close to the speed of light”; and cold dark matter, where “cold” means “particles moving at slower-than-relativistic velocities”.

Most observational evidence and current models favour cold dark matter, but the case is far from resolved. One test that can offer clues is whether small dark matter clumps can be found.


Hot dark matter, you see, would be moving too fast to allow for smaller chunks. If the dark matter is moving more slowly – as in cold dark matter theory – those small chunks should be out there.

However, finding them is not so easy. Remember the bit about how we can’t directly observe it? Instead, astronomers infer its presence based on the gravitational influence it has on the observable matter around it – stars that are moving too fast around the outer edges of galaxies, for example.

Another thing that gravity affects is light. If there is something really massive, such as a galaxy cluster, between us and a light source, the gravitational influence of that cluster curves spacetime, bending the path of the light and creating multiple images of the light source.

einstein cross(NASA, ESA, and D. Player/STScI)

This is called gravitational lensing, an effect predicted by Einstein’s general relativity. In rare instances, the objects involved are lined up in such a way that four distorted images are produced around the lensing object. This is called an Einstein cross.

What’s this got to do with cold dark matter, you are wondering? Well, here is the really cool part. The gravitational influence of small dark matter clumps should, in theory, be observable in differences found in each of the images of the background light source that are bent around the lens.


So, the team used the Hubble Space Telescope to study eight Einstein cross quasars, extremely bright galaxies powered by supermassive black holes, gravitationally lensed by massive foreground galaxies.

“Imagine that each one of these eight galaxies is a giant magnifying glass,” said UCLA astrophysicist Daniel Gilman.

“Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth.”

They measured how the light of the quasars is warped by the lens. They looked at the apparent brightness and position of each of the four images. And they compared these against predictions of how the Einstein crosses should look without dark matter.

These comparisons allowed the team to then calculate the mass of the dark matter clumps altering the images. These clumps seem to be between 10,000 and 100,000 times smaller than the mass of the dark matter in and around the Milky Way.

The findings don’t rule out the existence of hot dark matter, of course. (Not to even mention the added complication of mixed dark matter, a model that includes both types.) But these results do add a solid piece of evidence for the existing body of work supporting the existence of cold dark matter.

“Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter,” said astronomer and physicist Anna Nierenberg of NASA’s Jet Propulsion Laboratory.

“By combining the latest theoretical predictions, statistical tools, and new Hubble observations, we now have a much more robust result than was previously possible.”

The research has been presented at the 235th meeting of the American Astronomical Society, and published in the Monthly Notices of the Royal Astronomical Society.


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