humidity

Indoor air and outdoor pollution

July 11, 2025 By EarthWise Leave a Comment

The majority of us spend about 80% of our time indoors. The quality of the air that we breathe depends on the age and type of building we occupy along with any sources of indoor pollution that may exist and, ultimately, the quality of the air outdoors. The HVAC used to heat, ventilate, and cool the building plays an important role.

The College of Engineering at the University of Utah used its Salt Lake City campus as a living laboratory to explore how outdoor air pollution affects indoor air quality. Specifically, the nature of outdoor pollution sources strongly affected how effectively HVAC systems prevented external sources from getting into buildings.

Of particular concern is fine particulate matter with a diameter of less than 2.5 microns. These PM 2.5 particles can penetrate deeply into lungs, potentially causing health problems like respiratory irritation and heart disease.

There are multiple sources of PM 2.5. The Utah study found that wildfire smoke had four to five times more PM 2.5 infiltration into buildings than pollution from inversions and wind-driven dust events.

An additional finding was that commercial HVAC systems that use air-side economizers are much less effective at keeping out particulate matter. These systems use special duct and damper systems that reduce energy use by drawing air from outdoors when temperature and humidity levels are optimum.

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Does outdoor air pollution affect indoor air quality?

Photo, posted June 15, 2024, courtesy of Peter Burka via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Extreme heat and dairy production

May 6, 2025 By EarthWise Leave a Comment

Climate change is causing more frequent and intense heat waves in the United States. Studies show that not only are heat waves now occurring more often, but that the average heat wave season is nearly 50 days longer now than it was in the 1960s. The overall rise in temperatures, linked to climate change, has led to increased health risks and fatalities from extreme heat.

As humans face increasing health risks from this extreme heat, livestock are also suffering from the effects of rising temperatures. Extreme heat negatively impacts dairy production by causing heat stress in cows, which can reduce milk yield, quality, and the cows’ overall health.

A new study by researchers from the University of Illinois Urbana-Champaign analyzed milk production data from 18,000 dairy farms across nine Midwest states between 2012 and 2016. The researchers found that high heat and humidity have led to a 1% decline in annual milk yield. While this might not sound like a lot, it amounts to about 1.4 billion pounds of milk over five years from the 18,000 herds included in the study – equivalent to about $245 million in lost revenue.

The study, which was recently published in the journal Food Policy, found that small farms are hit harder than large farms. Larger farms may be able to mitigate some of the effects through management strategies, such as open barn sides, fans, and sprinklers.

Using projections from 22 different climate models, the research team estimates that more frequent extreme heat will increase milk yield losses by about 30% by 2050.

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Illinois study: Extreme heat impacts dairy production, small farms most vulnerable

Photo, posted March 13, 2018, courtesy of Gosdin via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Species range and climate change

July 23, 2024 By EarthWise Leave a Comment

The geographic range of a particular plant or animal species is the area in which it can be found during its lifetime. The range of most species is limited by climatic factors, including temperature, precipitation, soil moisture, humidity, and wind. Any changes in the magnitude or variability of these factors will impact the species living there.

For example, a species sensitive to temperature may respond to a warmer climate by moving to cooler locations at higher latitudes or elevations.

But not all species are able to move at the same speed. According to an international research team led by scientists from the University of Massachusetts Amherst, non-native species are expanding their ranges many times faster than native species.

The researchers found that land-based plant and animal species need to be shifting their ranges by about two miles per year just to keep up with the rapid pace of the changing climate. Marine species need to be moving about 1.7 miles per year. However, native species are only managing to move about one mile per year on average.

Non-native species, on the other hand, are spreading nearly 22 miles each year on their own. Additionally, when the role humans play in assisting the spread of non-native species is factored in, the rate jumps to a whopping 1,170 miles per year. This is more than 1,000 times faster than the rate at which native species are spreading.

The researchers conclude that there is no chance for native species to keep up with climate change without human help. Assisted migration needs to be on the table if native plants and animals are to survive.

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Non-Native Plants and Animals Expanding Ranges 100 Times Faster than Native Species

Photo, posted April 10, 2011, courtesy of Bri Weldon via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Carbon dioxide and wildfires

May 14, 2024 By EarthWise Leave a Comment

Climate change is a key factor in the increasing risk and extent of wildfires. Wildfires require the alignment of several factors, including humidity, temperature, and the lack of moisture in fuels, such as trees, shrubs, and grasses. All of these factors have strong ties to climate variability and climate change.

While the global surge in wildfires is often attributed to hotter and drier conditions, a new study by researchers from the University of California – Riverside has found that increasing levels of a greenhouse gas may be an even bigger factor.

According to the study, which was recently published in the journal Communications Earth & Environment, carbon dioxide is driving an increase in the severity and frequency of wildfires by fueling the growth of plants that become kindling.

Centuries of burning fossil fuels to produce heat, electricity and to power engines has added alarming amounts of carbon dioxide to the atmosphere. In fact, atmospheric CO2 levels are measuring more than 420 parts per million, which is a level not seen on earth for 14-16 million years.

Plants require carbon dioxide, along with sunlight and water, for photosynthesis. But rising levels of CO2 in the atmosphere are driving an increase in plant photosynthesis – an effect known as the carbon fertilization effect. This effect can make plants grow bigger and faster.

Warming and drying are important fire factors. These are the conditions that make the extra plant mass more flammable. But the study found that the increase in fires during hotter seasons is driven by the CO2-fueled growth of plants.

The researchers hope their findings will urge policymakers to focus on reducing carbon dioxide levels in the atmosphere.

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CO2 worsens wildfires by helping plants grow

Current carbon dioxide levels last seen 14 million years ago

Photo, posted January 17, 2024, courtesy of Jennifer Myslivy, BLM Fire/NIFC via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Too hot for people

November 22, 2023 By EarthWise Leave a Comment

The effort to mitigate the effects of climate change has a goal of keeping the global temperature increase below 1.5 degrees Celsius above preindustrial levels. To date, the average global temperature has increased by more than 1 degree. We hear about rising sea levels, powerful storms, and various other alterations in climate and weather patterns. A new interdisciplinary study by three institutions looked at the impact of surpassing the 1.5-degree level upon people being able to withstand heat and humidity.

Humans can only withstand certain combinations of heat and humidity before their bodies begin to experience heat-related health problems such as heat stroke and heart attacks.

In human history, temperatures and humidity that exceed human limits have been recorded only a limited number of times and only for a few hours at a time, in the Middle East and Southeast Asia.

According to the new study, if global temperatures increase by 2 degrees Celsius above preindustrial levels, the 2.2 billion residents of Pakistan and India’s Indus River Valley, the one billion people living in eastern China, and the 800 million residents of sub-Saharan Africa will annually experience many hours of heat surpassing human tolerance.

If the warming continues further to 3 degrees, heat and humidity levels that surpass human tolerance would affect the Eastern Seaboard and the middle of the US from Florida to New York and from Houston to Chicago.

The worst heat stress will occur in regions that are not wealthy and that are experiencing rapid population growth. But even wealthy nations will not escape from the expansion of conditions that are too hot for people.

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Climate-driven extreme heat may make parts of Earth too hot for humans

Photo, posted June 28, 2018, courtesy of Ivan via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Moisture swing carbon capture

November 10, 2023 By EarthWise Leave a Comment

As the world grapples with limiting the amount of carbon dioxide in the atmosphere, there is a growing need to capture the carbon dioxide that is emitted as well as preventing it from being emitted in the first place. Carbon capture can be accomplished at the source of emissions (such as power plants) or it can be done by taking it out of the atmosphere. The latter is called “direct air capture”.

It is not at all clear whether direct air capture can be accomplished on a scale that would really make a difference and at an acceptable cost either in dollars or energy expended. But if it can be done that way, it would be a major tool in combatting climate change.

Direct air capture technology generally makes use of sorbent materials whose capacity to capture carbon dioxide and later release it is a function of temperature. The process requires significant amounts of energy to release the carbon dioxide that has been captured.

New research from Northwestern University makes use of the “moisture-swing” technique which uses materials whose ability to capture and release carbon dioxide depends on humidity rather than temperature. While it takes some amount of energy to humidify the volume of air containing the sorbent material, it is very small compared to temperature-driven systems.

There are many groups working with moisture-swing technology, but the Northwestern Group has identified a number of new sorbent materials with superior properties.

The fundamental questions of scalability and cost remain, but moisture-swing is a promising approach to direct air capture. If carbon dioxide can be pulled out of the atmosphere in large volumes, it can be concentrated and stored or converted into useful products.

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Pulling carbon dioxide right out of the air

Photo, posted May 15, 2020, courtesy of James Watt via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Beavers As Climate Change Fighters | Earth Wise

October 25, 2022 By EarthWise Leave a Comment

California is fighting the effects of climate change on multiple fronts. The state has been grappling with relentless drought, record heat waves, and persistent wildfires. The California Department of Fish and Wildlife is enlisting the help of beavers in its battle against climate change.

The state has created a beaver restoration unit charged with developing methods for nature-based restoration solutions involving beavers as well as artificial beaver dams. The agency plans to spend at least $3 million over the next two years to oversee a restoration program for the North American beaver.

A 2020 study showed that beaver-dammed corridors were relatively unharmed by wildfires compared with other areas that lacked beaver damming. The study highlighted the differences between two adjacent corridors – one without a beaver population with a landscape scarred by a recent wildfire and another with beavers that remained a lush wetland after a fire. The differences in burn severity, air temperature, humidity, and soil moisture between the beaver complex and the adjacent landscape were huge.

From the 1920s through the 1950s, California actively exported beavers to other parts of the state and country so they could build dams in eroded areas where beaver dams could help evenly distribute water. Now, the state wants to reintroduce beavers into watersheds where they once flourished.

The Department of Fish and Wildlife’s proposal to the California Legislature called beavers an important keystone species that can be used to combat climate change. The state has spent enormous amounts of money on wildfire measures with minimal results. Now they are going to see if beavers can make a difference.

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California says the beaver can be superhero in fighting climate change

Photo, posted September 19, 2021, courtesy of Larry Lamsa via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

The Atmosphere Is Thirstier | Earth Wise

May 9, 2022 By EarthWise Leave a Comment

The American West is in the throes of a two-decade-long drought. The climate there is getting warmer and drier, which has led to increasing demand for water resources from both humans and ecosystems. According to a new study by the Desert Research Institute and collaborators, the atmosphere across much of the U.S. is also demanding a greater share of water than it used to.

Evaporative demand, which is also called atmospheric thirst, is a measure of the potential loss of water from the earth’s surface up to the atmosphere. It is a function of temperature, humidity, wind speed, and solar radiation. The study, published in the Journal of Hydrometeorology, assessed trends in evaporative demand during a 40-year period from 1980-2020.

The study’s findings showed substantial increases in atmospheric thirst across much of the Western U.S. over that period, with the largest increases centered around the Rio Grande and Lower Colorado rivers. This is important because atmospheric thirst is a persistent force in pushing Western landscapes and water supplies toward drought.

The study found that, on average, increases in temperature were responsible for 57% of the changes observed in atmospheric thirst, humidity 26%, and the other factors playing lesser roles.

For farmers and other water users, increases in atmospheric thirst mean that, in the future, more water will be required to meet existing water needs. Crops already require more water than they did in the past and can be expected to require more water in the future. Over time, for every drop of precipitation that falls, less and less water is likely to drain into streams, wetlands, aquifers, or other water bodies.

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New study shows robust increases in atmospheric thirst across much of U.S. during past 40 years

Photo, posted August 9, 2007, courtesy of William Clifford via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Climate Change On Mount Everest | Earth Wise

March 21, 2022 By EarthWise Leave a Comment

Climate change has shown up in the highest place on Earth. The highest glacier on Mount Everest is rapidly retreating with rising temperatures.

New research by an international team led by the University of Maine and published in the journal Climate and Atmospheric Science has determined that the South Col Glacier atop Mount Everest has shrunk by half since the 1990s. Its ice mass has thinned by an estimated 180 feet.

The glacier used to be covered by snow, which reflected the sun’s light and insulated the mass of ice under the snow. But warmer temperatures, lower humidity, and more severe winds have eliminated the snow cover, fueling the decline of the glacier.

The study of the South Col Glacier highlights the critical balance created by snow-covered surfaces and exposes the potential for loss throughout high mountain glacier systems as snow cover is depleted by warming temperatures. When even the highest glacier on Mount Everest is impacted, it is clear that no place is safe from the warming climate.

The human significance of this development is substantial. More than 200 million people in Asia depend on meltwater from glaciers in the high mountains of the continent for their freshwater needs. But now glaciers in the mountains are melting faster than they can be replenished by snowfall.

As for Mount Everest itself, future expeditions on the mountain will face new challenges as glacier melting causes more avalanches and climbers accustomed to digging into ice and snow will need to scale more exposed bedrock. Climate predictions for the Himalaya in general all anticipate continued warming and continued loss of glacier mass.

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Climate Change Has Reached the Top of Mount Everest, Thinning Its Highest Glacier

Photo, posted October 27, 2011, courtesy of Goran Hogland via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Deadly Urban Heat On The Rise | Earth Wise

November 9, 2021 By EarthWise Leave a Comment

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

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Earth Wise is a production of WAMC Northeast Public Radio.

Reduced Air Travel And Weather Forecasts | Earth Wise

December 16, 2020 By EarthWise Leave a Comment

There have been countless stories about the major and minor changes in the world caused by the Covid-19 pandemic. A few of those changes, such as reductions in pollution and traffic, have been positive. Most have been decidedly negative.

One of the stranger things that has happened is that the pandemic has affected the quality of weather forecasting by sharply reducing the amount of atmospheric data routinely collected by commercial airliners.

It turns out that atmospheric observations from passenger and cargo flights are among the most important data used in weather forecasting models. These observations are made by instruments aboard thousands of airliners, mostly based in North America and Europe. The observation program has been in place for decades. The data is transmitted in real time to forecasting organizations around the world, including the National Weather Service. About 40 airlines participate in the program, which has equipment aboard about 3,500 aircraft. Here in the US, Delta, United, American, and Southwest Airlines participate, as do UPS and FedEx.

During the first few months of the pandemic, air traffic declined by 75% or more worldwide. As a result, atmospheric observations dropped by the same percentage. A government research study showed that when weather forecasting models receive less data on temperature, wind, and humidity from aircraft, the accuracy of forecasts was reduced.

The amount of data from aircraft has increased in recent months as air travel has picked up to roughly 50% of pre-pandemic levels. So, the observation program is on the mend. Nonetheless, impaired weather forecasting is just another unexpected result of the global pandemic.

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Slump in Air Travel Hindered Weather Forecasting, Study Shows

Photo, posted July 15, 2017, courtesy of Daria Nepriakhina via Flickr. Photo by Photo by Daria / epicantus.

Earth Wise is a production of WAMC Northeast Public Radio.

Extreme Heat And Humidity | Earth Wise

June 15, 2020 By EarthWise Leave a Comment

On hot, sticky summer days, one often hears the expression “it’s not the heat, it’s the humidity.” That isn’t just an old saw; it is a recognition of what might be the most underestimated direct, local danger of climate change. Extreme humid heat events represent a major health risk.

There is an index called “wet-bulb temperature” that is calculated from a combination of temperature and humidity data. The reading, which is taken from a thermometer covered in a wet cloth, is related to how muggy it feels and indicates how effectively a person sheds heat by sweating. When the wet-bulb temperature surpasses 95^o Fahrenheit, evaporation of sweat is no longer enough for our bodies to regulate their internal temperature. When people are exposed to these conditions for multiple hours, organ failure and death can result.

Climate models project that combinations of heat and humidity could reach deadly thresholds for anyone spending several hours outdoors by the end of this century.

Dangerous extremes only a few degrees below the human tolerance limits – including in parts of the southwestern and southeastern US – have more than doubled in frequency since 1979. Since then, there have been more than 7,000 occurrences of wet-bulb temperatures above 88^o, 250 above 91^o, and multiple reading above 95^o. Even at lower wet-bulb temperatures around 80^o, people with pre-existing health conditions, the elderly, as well as those performing strenuous outdoor labor and athletic activities, are at high risk.

More research is needed on the factors that generate extreme wet-bulb temperatures as well as the potential impacts on energy, food systems, and human security.

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Dangerous Humid Heat Extremes Occurring Decades Before Expected

Photo, posted April 16, 2012, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Off-The-Charts Heat

August 9, 2019 By EarthWise Leave a Comment

There have been some blistering heatwaves this summer – in Europe, in the Middle East, and here in the United States. A new report by the Union of Concerned Scientists projects that within the next 20 years, millions of people in the United States could be exposed to dangerous “off-the-charts” heat index conditions of 127 degrees Fahrenheit or more. Within 60 years, over one-third of the population could be exposed to such conditions.

Extreme heat kills hundreds of people every year across the U.S. Our bodies’ natural cooling process is affected by humidity and the combined heat index measures the impact of high temperature and high humidity. When the combined heat index reaches 90 degrees, it is considered to be a “dangerous day”, when many groups of people are at serious risk.

Because of the warming climate, the number of dangerous days has been increasing in many parts of the country. Unless there is success in limiting the effects of climate change, by 2050, even relatively temperate cities like Detroit, Minneapolis, New York, and Chicago will have 50 or more dangerous days a year. Places like Dallas, Houston, Phoenix and Miami will experience dangerous days for half of the year.

The National Weather Service’s heat index goes up to 127 degrees Fahrenheit. But in as soon as 20 years, the Southeast, Southern Great Plains, and Midwest will begin to experience days that are so hot that they are “off the charts.”

These extreme conditions could still be avoided with steep, rapid carbon emission reductions. But however successful we are going forward, the US will still be significantly warmer than today with 85 urban areas exposed to 30 or more days with a heat index above 105 degrees, compared with just three urban areas historically.

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