Less than a month into North America’s official summer, heat waves are blistering much of the West. California and the Southwest are facing excessive heat watches for the second time, after a mid-June heat wave pushed temperatures above 100 F (38 C).

And in late June an intense heat dome settled over the Pacific Northwest for four days, setting all-time temperature records in Oregon, Washington and British Columbia. The effects were most evident in Lytton, British Columbia, which reported a temperature of 121 F (49.5 C) on June 29, far above its average high for the date of 76 F (24.4 C). A day later, the town was engulfed by a wildfire.

As an exercise physiologist, I know that the human body is an amazing machine. But like all machines, it functions effectively and safely only under certain conditions.

People frequently debate whether wet heat in places like Florida or dry heat in desert locations like Nevada is worse. The answer is that either setting can be dangerous. Hot desert climates are stressful due to extreme temperatures, while humid subtropical climates are stressful because the body has trouble removing heat when sweat doesn’t evaporate readily. As recent events have shown, hot is hot.

The influence of humidity

North America has a wide range of climates, but when people talk about heat, they often compare the Southwest and the Southeast. Some communities in the Southwest’s hot desert climates, such as Las Vegas, have average summer high temperatures over 100 F (38 C), with relative humidity typically around 20%. This means the air is holding about one-fifth of the maximum amount of moisture it can hold at that temperature and pressure.

In contrast, Southeast locations like Orlando, Florida, typically have average temperatures around 90 F (32.2 C), with humidity regularly approaching 80%. Looking only at temperature, the desert clearly is hotter on average.

However, it’s also important to consider how heat affects the body. Weather reports often do this using the heat index, which calculates how the human body perceives conditions factoring in humidity as well as heat.

Sweating is your body’s primary way of cooling you off. When sweat evaporates away from your skin, it takes heat with it. But when humidity is high, the air already holds a lot of moisture, so the sweat remains on your skin. As it saturates clothing and drips from the body, it can remove only a small amount of heat compared with the cooling that comes with the evaporation of sweat.

As a result, when we account for humidity, the heat exposures people experience in Las Vegas and Orlando are very similar.

Adapting people and places to heat stress

As people go through their daily lives, their bodies work continuously to maintain a temperature close to a normal level of about 98.6 F (37 C). In regions that regularly experience high heat stress, such as the Southeast and Southwest, most buildings and homes now have air conditioning, which helps people maintain healthy temperatures.

But in areas where heat is unusual, such as the Pacific Northwest, many buildings and residences lack cooling. As a result, people are exposed to higher heat for longer periods of time during events like the region’s late June heat wave than they would be in regions where hot weather is the norm.

Just as buildings and residences in areas chronically exposed to heat are equipped with ceiling fans and air conditioning, bodies that are regularly exposed to heat can acclimatize, or adapt and improve their ability to cool. This starts to occur with the first heat exposure – for example, the beginning of fall sports practices in August – but take weeks of regular exposure to reach maximal levels.

One of the first things our bodies do in adapting to heat is to produce more plasma – the watery portion of blood. This enables our circulatory systems to move heat to the skin more effectively so that sweating can remove it from the body.

We also begin sweating earlier than people who are not acclimatized to heat, and our maximal sweat rate increases. These adaptations improve our bodies’ ability to dissipate heat to the environment.

Behavior changes are another way of adapting to heat stress. Since midday is typically the hottest part of the day, it makes sense to avoid physical work and exercise then. When people are active, their bodies break down nutrients – carbohydrates, fats and protein – into energy. This powers movement and also generates metabolic heat, which adds to the body’s heat stress.

Taking advantage of shade is another important strategy. Heat radiating from the Sun adds to the stress produced by warm air temperatures. Staying in the shade can significantly reduce the external heat load on people who have to be outdoors during hot spells.

Many of the hundreds of deaths and hospitalizations that experts have attributed to the recent heat dome in the Northwest probably reflect that buildings there were less equipped to keep people cool than in hotter regions, and residents were less acclimatized to heat.

The old and young are most vulnerable

A healthy adult body can acclimatize to heat, but older people and children are less able to adjust. As people age, their cardiovascular systems change in ways that cause them to pump blood less effectively. This reduces the body’s ability to move heat to the skin to be transferred to the environment.

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Children and older adults may also have less active sweat responses, which can reduce their potential to cool off through sweating.

Humans can tolerate most areas of the Earth, but extreme heat requires extra steps. If there’s a heat wave in your local forecast, seek out shade and begin to acclimatize by increasing your activity gradually when things get too hot. Drink more fluids to account for increased fluid loss from sweat, while also making sure not to overhydrate. And avoid outdoor activity during the hottest hours of the day if possible.

Whether heat waves are humid or dry, they are health threats that everyone should take seriously.

JohnEric W. Smith, Associate Professor of Exercise Physiology, Mississippi State University

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Plastic is the most common type of debris floating in the world’s oceans. Waves and sunlight break much of it down into smaller particles called microplastics – fragments less than 5 millimeters across, roughly the size of a sesame seed.

To understand how microplastic pollution is affecting the ocean, scientists need to know how much is there and where it is accumulating. Most data on microplastic concentrations comes from commercial and research ships that tow plankton nets – long, cone-shaped nets with very fine mesh designed for collecting marine microorganisms.

But net trawling can sample only small areas and may be underestimating true plastic concentrations. Except in the North Atlantic and North Pacific gyres – large zones where ocean currents rotate, collecting floating debris – scientists have done very little sampling for microplastics. And there is scant information about how these particles’ concentrations vary over time.

To address these questions, University of Michigan research assistant Madeline Evans and I developed a new way to detect microplastic concentrations from space using NASA’s Cyclone Global Navigation Satellite System. CYGNSS is a network of eight microsatellites that was launched in 2016 to help scientists predict hurricanes by analyzing tropical wind speeds. They measure how wind roughens the ocean’s surface – an indicator that we realized could also be used to detect and track large quantities of microplastics.

Looking for smooth zones

Annual global production of plastic has increased every year since the 1950s, reaching 359 million metric tons in 2018. Much of it ends up in open, uncontrolled landfills, where it can wash into river drainage zones and ultimately into the world’s oceans.

Researchers first documented plastic debris in the oceans in the 1970s. Today, it accounts for an estimated 80% to 85% of marine litter.

The radars on CYGNSS satellites are designed to measure winds over the ocean indirectly by measuring how they roughen the water’s surface. We knew that when there is a lot of material floating in the water, winds don’t roughen it as much. So we tried computing how much smoother measurements indicated the surface was than it should have been if winds of the same speed were blowing across clear water.

This anomaly – the “missing roughness” – turns out to be highly correlated with the concentration of microplastics near the ocean surface. Put another way, areas where surface waters appear to be unusually smooth frequently contain high concentrations of microplastics. The smoothness could be caused by the microplastics themselves, or possibly by something else that’s associated with them.

By combining all the measurements made by CYGNSS satellites as they orbit around the world, we can create global time-lapse images of ocean microplastic concentrations. Our images readily identify the Great Pacific Garbage Patch and secondary regions of high microplastic concentration in the North Atlantic and the southern oceans.

Tracking microplastic flows over time

Since CYGNSS tracks wind speeds constantly, it lets us see how microplastic concentrations change over time. By animating a year’s worth of images, we revealed seasonal variations that were not previously known.

We found that global microplastic concentrations tend to peak in the North Atlantic and Pacific during the Northern Hemisphere’s summer months. June and July, for example, are the peak months for the Great Pacific Garbage Patch.

Concentrations in the Southern Hemisphere peak during its summer months of January and February. Lower concentrations during the winter in both hemispheres are likely due to a combination of stronger currents that break up microplastic plumes and increased vertical mixing – the exchange between surface and deeper water – that transports some of the microplastic down below the surface.

This approach can also target smaller regions over shorter periods of time. For example, we examined episodic outflow events from the mouths of the China’s Yangtze and Qiantang rivers where they empty into the East China Sea. These events may have been associated with increases in industrial production activity, or with increases in the rate at which managers allowed the rivers to flow through dams.

Better targeting for cleanups

Our research has several potential uses. Private organizations, such as The Ocean Cleanup, a nonprofit in The Netherlands, and Clewat, a Finnish company specializing in clean technology, use specially outfitted ships to collect, recycle and dispose of marine litter and debris. We have begun conversations with both groups and hope eventually to help them deploy their fleets more effectively.

Our spaceborne imagery may also be used to validate and improve numerical prediction models that attempt to track how microplastics move through the oceans using ocean circulation patterns. Scholars are developing several such models.

While the ocean roughness anomalies that we observed correlate strongly with microplastic concentrations, our estimates of concentration are based on the correlations that we observed, not on a known physical relationship between floating microplastics and ocean roughness. It could be that the roughness anomalies are caused by something else that is also correlated with the presence of microplastics.

One possibility is surfactants on the ocean surface. These liquid chemical compounds, which are widely used in detergents and other products, move through the oceans in ways similar to microplastics, and they also have a damping effect on wind-driven ocean roughening.

Further study is needed to identify how the smooth areas that we identified occur, and if they are caused indirectly by surfactants, to better understand exactly how their transport mechanisms are related to those of microplastics. But I hope this research can be part of a fundamental change in tracking and managing microplastic pollution.

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Christopher Ruf, Professor of Climate and Space Sciences and Engineering, University of Michigan

This article is republished from The Conversation under a Creative Commons license. Read the original article.