Air Quality Concerns in Sequoia National Park

Situated high is California’s Sierra Nevada Mountains, Sequoia National Park protects the only place on Earth where giant sequoias – the world’s largest trees by volume – grow naturally. Air pollution, however, does not recognize the boundaries set up by the National Park Service (NPS). While hiking there recently, I learned more about the air quality issues facing this national natural treasure.

According to a recent report by the National Parks Conservation Association, Sequoia National Park received an “F” for air quality. While other parks in the NPS system also have air quality concerns, Sequoia NP was rated the worst in the nation. In 2014, its Ash Mountain monitoring station recorded 56 days where the level of ozone was above federal health standards.

In most parts of the country, air quality issues are often connected to emissions from coal-fired power plants, but in California there are a few other factors at play. While the region’s notorious wildfires do create some air quality problems, the NPS says the vast majority of the pollution in the park comes from human activities outside its borders. With a prevailing westerly wind in the region during the summer months, emissions from large-scale industrial and agricultural activities as well as massive amounts of vehicle exhaust are swept eastward from San Francisco and across the San Joaquin Valley. Trapped by the topography of the valley, the polluted air is heated and forced to rise up to the elevation of the park. Pollutants found in the air include nitrogen oxides, ground level ozone, fine particulate matter, and traces of pesticides.

Of these pollutants, ground level ozone, which forms when nitrogen oxides react with heat and U.V. light, poses the most serious threat to human health. It is known to cause a variety of repository problems and is often the reason given for air quality alerts.  It is also harmful to plants and trees – the organisms that are supposed to be protected by the park.

While ozone does not seem to be impacting mature sequoias, the NPS says experiments have shown that it is stunting the growth of sequoia seedlings. That said, other trees in the park, such as Ponderosa and Jeffrey Pines are feeling its full effect. Damaging their stomata – tiny pores on their needles that usually absorb carbon dioxide -the pollutant reduces a tree’s ability to perform photosynthesis and therefore its ability to produce and store food.  As a result, they are weakened and more susceptible to disease and insects. The telltale sign of ozone damage is the yellowing and thinning of a conifer’s needles.

Air pollution is also responsible for the smog that obscures views in the park. On a clear day, according the NPS, the view from Beetle Rock – which is about 6,200 feet above sea level – extends for more than 100 miles. In summer, when the smog is worst, that view is often significantly reduced.

The good news is that air quality issues in the park – like much of the rest of the country – have improved in recent years as a result of measures associated with the Clean Air Act. The bad news is that it still remains a serious problem. Seeing that our actions can make a difference, we can continue to reduce air pollution by conserving energy and reducing emissions – a similar strategy to reducing the impacts of climate change.

View from the edge of Giant Forest. Credit: NPS

A view looking southwest from the edge of Giant Forest in Sequoia National Park. Credit: NPS

Pyrocumulus Cloud Forms Over Wildfire in Kings Canyon National Park

Fueled by drought, wildfires have been blazing across the American West all summer.   Sixteen are currently burning in California alone. While hiking in Kings Canyon National Park in the state’s rugged Sierra Nevada Mountains recently, I crossed paths with the “Rough Fire” and saw it produce a billowing pyrocumulus cloud.

Pyrocumulus clouds form when intense heat at the surface – usually from a wildfire or volcanic eruption – causes air to rise rapidly. As it travels upward, water vapor in the air condenses into droplets and forms a cloud. Filled with ash and smoke, the swelling cloud generally appears more grey than white.

Ignited by lightning over three weeks ago, the Rough Fire continues to spread and has even caused parts of Kings Canyon National Park to close. According to the NPS, smoke from the massive fire has also impacted the air quality in and around the park. To date, the fire has charred close to 50,000 acres and is only 17% contained.

Pyrocumulus cloud rising over California's Rough Fire in Sierra National Forest and Kings Canyon National Park. August 2015. Credit: The Weather Gamut.

Pyrocumulus cloud rising over California’s Rough Fire in Sierra National Forest and Kings Canyon National Park, August 2015. Credit: The Weather Gamut.

July 2015: Warmest Month on Record for Planet Earth

Our global temperature continued its upward trend last month with July 2015 marking not only the warmest July on record, but the warmest month ever recorded for the entire planet.

According to a report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for the month – over both land and sea surfaces – was 61.86°F, which is 1.46°F above the 20th century average. It surpassed the previous record set in 1998, which was also an El Niño year, by 0.14°F.

July 2015 also marked the 39th consecutive July that our global temperature was above its long-term norm. NOAA says that July – which is climatologically the planet’s warmest month – has been getting hotter over the years. Records show that the temperature for the month is currently increasing at an average rate of 1.17°F per century.

For the oceans, the globally averaged sea surface temperature for the month was 1.35°F above the 20th century average of 61.5°F.  That is the highest departure on record for any month. According to NOAA, the ten highest monthly departures from average for ocean temperatures have all occurred since April 2014.

While heat dominated most of the planet in July, some places were particularly warm. Heat waves in Europe pushed temperatures to record levels across the region. In fact, it was the warmest July on record for both Austria and Spain. Here in the contiguous US, temperatures were slightly warmer than average, but no state set a new record high. This difference highlights the fact that climate change is a complex global phenomenon that involves much more than what is happening in our own backyards.

Year to date, the first seven months of 2015 were the warmest of any year on record. Global temperature records date back to 1880.

Credit: NOAA

Credit: NOAA

First Heat Wave in NYC Since 2013

It’s official! We’re having a heat wave in New York City.

While we have hit the 90°F mark a few times already this summer, this is the first real heat wave of the season. Actually, it is the first official heat wave in the Big Apple since 2013.

The threshold for what constitutes a heat wave varies by region, but here in the NYC area it is defined as three consecutive days with temperatures reaching 90°F or higher. In Central Park, the temperature reached 92°F on Saturday, 93°F on Sunday, and today it climbed to 95°F – tying the record high for the date.

When factoring in the high levels of humidity these past few days, the heat index felt like it was near 100°F. While these conditions are oppressive, they can also be dangerous. Both a heat advisory and air quality alerts were issued for the city.

For most of the summer, temperatures have been running slightly above average in NYC, but it is interesting to note that there has not been much extreme heat. To date, we have only had ten days with readings at or above 90°F. On average, we typically see fifteen for the season.

The Hottest Days of Summer Vary By Region

For the continental U.S. as a whole, the hottest part of summer arrives in mid to late July. On the regional level, however, there are significant differences in the timing of the hottest part of the season.

Based on historical averages, NOAA’s National Centers for Environmental Information (NCEI) produced a map showing how the warmest days of summer vary across the country. The desert southwest, for example, is an early bloomer in terms of heat.  It’s warmest days typically arrive in June.  By early July, the North American Monsoon – a seasonal shift in wind direction – kicks in and helps keep the region relatively cool and rainy through September.

In parts of the south central states, a persistent area of high pressure typically builds over the region in August. This limits cloud formation and dries out the soil, which helps to send temperatures skyrocketing.

On the other far end of the spectrum, temperatures along the west coast do not peak until September. This lag is the result of hot air rising over interior deserts and cool Pacific air flowing in-land.  By September, this upper-level wind pattern usually weakens and allows warm air to flow toward the coast.

While the NCEI map is derived from long-term climate averages, it is important to note that short-term variability can cause the date of peak temperatures to vary in any given year.



The Positive and Negative Sides of Cloud to Ground Lightning

Thunderstorms can illuminate the sky with a number of different types of lightning. The most threatening to us at the surface, however, is the cloud to ground variety. Interestingly, it comes in two forms: positive and negative.

While not completely understood, lightning – an intense electrical discharge – is believed to form as a result of the separation of charges in a cumulonimbus cloud. Within these towering clouds, both negatively charged hailstones and positively charged ice-crystals exist at the same time. As the storm’s updraft moves through the cloud, the lighter ice-crystals are carried upward, leaving the denser hailstones to fall to the bottom.

As the negative charge builds at the base of the cloud, it induces a strong positive charge on the ground, especially in tall objects such as buildings and trees. When the charge separation becomes large enough, a negatively charged stepped leader, a channel of ionized air, initiates a lightning strike from the base of the cloud. Moving down toward the ground, it meets a channel of rising positive charges known as a streamer. When they connect, they form negative cloud to ground lightning (-CG), which is the most common type.

Positively charged lightning (+CG), on the other hand, originates in the upper section or anvil of a cumulonimbus cloud. In this case, the descending stepped leader carries a positive charge and travels horizontally as it makes its way toward an area with negatively charged particles on the ground. It can travel more than 10 miles – a distance where thunder from the parent storm cannot be heard – to areas with relatively clear skies. For this reason, positive lightning is often called a “bolt from the blue”.  It is most often associated with super cell thunderstorms and is considered rare. According to NOAA, it makes up less than 5% of all lightning strikes.

While uncommon, positive lightning is extremely powerful. Originating at a higher level of a storm cloud, it has to travel through more air to reach the ground, intensifying its electrical field. Its peak charge can be 10 times greater than that of a negative strike. This immense power combined with a lack of warning makes positive cloud to ground lightning particularly dangerous. It is also believed to be responsible for a large percentage of wildfires.

To visually identify positive and negative cloud to ground lightning, look at the shape of the bolt. Negative lightning will have a downward branching pattern and positive lightning will generally display a single bright stroke without branches.

Regardless of these differences in charge and shape, it is important to remember that all lightning is dangerous. Stay safe!

Negative Cloud to Ground Lightning.  Credit: NOAA

Negative Cloud to Ground Lightning. Credit: NOAA

Positive Lightning.  Credit: MD Weather

Positive Lightning. Credit: MD Weather

NYC Monthly Summary: July 2015

July is normally the warmest month on the calendar for New York City, and this year was no exception. Despite getting off to a relatively cool start, the month brought us five days with temperatures in the 90s. These hot days helped bring the city’s mean temperature for the month up to 78.8°F, which is 2.3°F above average.

While we had a few stretches of very warm and humid days, including some where the heat index reached  the triple digits, it is interesting to note that we did not technically have a single heat wave all month. In this part of the US, a heat wave is defined as three consecutive days with temperatures reaching 90°F or higher.

On the precipitation side of things, NYC was mostly dry. In all, we received 3.98 inches of rain in Central Park, which is 0.62 inches below average. Of this total, 1.95 inches fell in a single day as a cold front moved through the area triggering thunderstorms and intense downpours.  July is typically the wettest month of the year in the Big Apple.