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Harmful algal blooms and climate change

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An algal bloom is a rapid increase in the density of algae in an aquatic system.  Harmful algal blooms occur when bodies of water get overloaded with nitrogen and phosphorus runoff from agriculture and other human activities. These excess nutrients can facilitate the out-of-control growth of cyanobacteria, also known as blue-green algae. 

Some species of blue-green algae produce a toxin called microcystin.  These toxins pose a serious health hazard to people, animals, and the environment.  Microcystin affects liver function and can cause death in animals, as well as humans in rare instances.  A notable incident occurred in the summer of 2014, when cyanobacteria contamination in Lake Erie left 500,000 residents in Ohio and Michigan without water for 72 hours and sickened more than 100 people. 

According to a study led by researchers from Carnegie Science, as climate change warms the earth, higher-latitude regions will be at a greater risk for microcystin produced by algal blooms.  The study found water temperatures of 68 to 77 degrees Fahrenheit as being at the greatest risk for developing dangerous levels of microcystin. 

In the study, which was published in the journal Nature Water, the research team also demonstrated that the areas most susceptible to high toxin concentrations will continue to move northward. And in some areas, researchers say the relative risk of exceeding water quality guidelines will increase by up to 50% in the coming decades.

The research team hopes its findings raise more awareness about water sustainability, and the need to focus on the quality of the water as much as the quantity of water. 

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Geographic redistribution of microcystin hotspots in response to climate warming

Photo, posted October 27, 2010, courtesy of Nara Souza / Florida Fish and Wildlife Commission via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Deadly Heatwaves On The Rise | Earth Wise

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The European heatwave in the summer of 2003 resulted in at least 30,000 deaths with more than 14,000 in France alone. At the time, such a heatwave was considered to be a once-in-a-hundred-year event. But the warming climate is dramatically changing the odds for deadly heatwaves.

A new study by the ETH Institute in Zurich has found that the risk of fatal heatwaves has risen sharply over the past 20 years, and in the future, such extreme weather will become more frequent and heat-related excess mortality will increase, particularly in Europe.  According to a paper published in Nature Medicine, more than 61,000 deaths in Europe could be blamed on the heat during the summer of 2022, which was the hottest summer on record for the continent.  When the readings from this summer are analyzed, that record is likely to be surpassed.

Heatwaves lead to excess deaths due to dehydration, heat stroke, and cardiovascular collapse.  They are particularly deadly for the elderly, the sick, and the poor.  The ETH researchers analyzed comprehensive data from 748 cities and communities in 47 countries.   They determined the relationship between increased temperature and excess mortality.  Their models look at how excess mortality would develop with an average global temperature increase of 0.7 degrees Celsius (the value in 2000), 1.2 degrees (the value in 2020), and both 1.5 degrees (the limit sought by the Paris Agreement) and 2 degrees.

Even with the current global temperature, heatwaves that were a once-in-a-century event are now expected to occur every 10 years.  With 2 degrees of warming, such heatwaves could happen every 2 to 5 years.

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Heatwaves are becoming more frequent and more deadly

Photo, posted July 22, 2009, courtesy of Matt McGee via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Deadly Urban Heat On The Rise | Earth Wise

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According to a new study by the Columbia Climate School, exposure to deadly urban heat has tripled since the 1980s.  The increase is the combined result of both rising global temperatures and booming urban population growth.

The study looked at more than 13,000 cities worldwide and found that incidents of extreme heat and humidity have increased dramatically.   It defined extreme heat as 30 degrees Celsius on the wet-bulb temperature scale that takes into account the effect of high humidity.  In 1983, there were 40 billion person-days under such conditions.  By 2016, the number was 119 billion.  More specifically, in 2016 1.7 billion people were subjected to such conditions on multiple days.

Sheer urban population growth accounted for two-thirds of the increase, while actual warming contributed a third.  Over recent decades, hundreds of millions of people have moved from rural areas to cities, which now hold more than half the world’s population.  And because of the urban heat island effect, temperatures in cities are generally higher than in the countryside.

In the United States, about 40 sizable cities have seen rapidly growing exposure to extreme heat, mainly clustered in Texas and the Gulf Coast.  Globally, nearly a quarter of the world’s population is affected by the increased incidence of extreme temperatures.

A study last year showed that combinations of heat and humidity literally beyond the limits of outdoor human survival have been popping up around the world.  A wet-bulb temperature reading of 30 – equivalent to 106 degrees Fahrenheit on the “real feel” heat index – is the point at which even most healthy people find it hard to function outside for long, and the unhealthy might become very ill or even die.

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Exposure to Deadly Urban Heat Worldwide Has Tripled in Recent Decades, Says Study

Photo, posted March 5, 2007, courtesy of Michael Phillips via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

WAMC Northeast Public Radio

WAMC/Northeast Public Radio is a regional public radio network serving parts of seven northeastern states (more...)