The goal of COP 21 – the massive UN Climate Change Conference in Paris – is to limit global warming to 2°C (3.6°F) above pre-industrial levels by reducing greenhouse gas emissions around the world. But why, you may wonder, is 2°C the target and what happens if we pass it? Below is a short video by Climate Central, a non-profit news organization, that addresses these important questions.
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
Positive Lightning. Credit: MD Weather
Summer is wildfire season in the American West, and it is off to a raging start.
So far this year, according to the National Interagency Fire Center, wildfires have burned 5.5 million acres across the US. That is an area roughly the size of the state of New Jersey. It is also the second highest total (as of this date) in the last 25 years.
As of Monday, 22 large wildfires – defined as greater than 100 acres – are burning in 5 states. In California’s Napa Valley region, the Wragg Fire has scorched 7,000 acres and forced many residents to evacuate. In Montana, a massive blaze has burned approximately 5 square miles of Glacier National Park since it began last week. The majority of the acres burned, however, have been in Alaska. They have seen nearly 4.7 million acres charred, which is about 85% of the national total to date.
High temperatures and prolonged drought in the West have turned forests and brush areas into tinderboxes that are susceptible to any type of spark. While summer is usually hot and dry in California, the state is enduring its fourth year of drought. Alaska has also been unusually warm and dry. In fact, according to NOAA, they are in the middle of their second warmest year on record, year to date. These warm temperatures helped produce a dearth of winter snowfall, which has lead to drier than normal conditions across a large area of the state.
Overall, wildfires in the US seem to be getting worse. In Alaska, 3 of the worst wildfires have occurred in the last 12 years. In California, 12 of their 20 largest fires have taken place since 2000. In both states, wildfire records date back to the 1930s.
Nationally, summer 2015 is on track to be one of the worst wildfires seasons on record.
Wildfire rages in Glacier National Park, Montana. Image Credit: CBS
Summer is the season for thunderstorms and the lightning they produce can light up the sky in a variety of ways. Here is a quick look at the different types of lightning.
While there are variations within each, these are the four primary categories:
Intra-Cloud: This is the most common type of lightning. It happens completely inside a single cloud, jumping between regions with different charges. It is sometimes called “sheet” lightning.
Cloud to Cloud: This is lightning that occurs between two or more separate clouds.
Cloud to Air: This type of lightning occurs when positive charges at the top of a cloud reach out to the negatively charged air around it.
Cloud to Ground: This lightning occurs between the cloud and the ground. It can be either positively or negatively charged.
While thunderstorms can be fascinating things to watch, is important to remember that all lightning is dangerous and strike locations are unpredictable. So, as NOAA recommends, “When Thunder Roars, Go Indoors.”
Different types of lightning. Credit: mshuntergi.com
Summer vacation season has arrived and millions of people will be heading to beaches to beat the heat over the next few months. As such, it is important to remember that the ocean is a dynamic environment that can pose a number of hazards for swimmers. Chief among these are rip currents.
Rip currents are fast, localized channels of water moving away from the shoreline. According to NOAA, they are a result of “complex interactions between waves, currents, water levels and nearshore bathymetry.” They can form in several different ways on any beach with breaking waves. That said, they are typically found at breaks in sandbars and along permanent structures that extend out into the water such as jetties or piers.
Moving at up to 8 feet per second – which is faster than an Olympic swimmer – rip currents can easily drag unsuspecting swimmers hundreds of yards out to sea. While they will not pull anyone underwater, they can cause fatigue and panic. According to the U.S. Lifesaving Association, rip currents are responsible for 80% of all surf zone rescues. Nationally, they cause more than one hundred deaths every year.
To spot a rip current, look for a gap in the breaking waves. This is where the water is forcing its way back out to sea. The water in this area is also usually murky and darker than the surrounding water. On guarded beaches, red flags indicate hazardous conditions for swimmers.
If caught in a rip current, the Red Cross recommends not trying to swim against it. Instead, they say to swim parallel to the shoreline until you are out of the current. Once free, you can start swimming back toward the beach.
For more information on beach safety, visit: http://www.redcross.org/prepare/disaster/water-safety/beach-safety
Image Credit: NOAA.
Torrential rain events and the flooding they cause are nothing new. Global warming, however, is helping to make them more likely.
According to the most recent National Climate Assessment, heavy rain events – defined as the heaviest 1% of all rain events – have become heavier and more frequent across most of the US. The greatest increases have been observed in the northeast, mid-west, and southeast.
Climate scientists attribute this increase in heavy precipitation to our warming atmosphere. Simply put, warm air holds more moisture than cold air. And, the more moisture that builds up in the air, the more rain can fall.
The relentless rain and deadly floods in Texas last month made national headlines, but there are many other examples of similar events in the recent past. In September 2013, Colorado experienced catastrophic flooding caused by overwhelming amounts of rain in a short period of time. Locally, here in the NYC area, the town of Islip on Long Island saw more than 13 inches of rainfall in a single day last August. That equates to 29% of their average annual rainfall. The damage caused by that single event was estimated at $35 million.
As our global temperature continues to rise, experts say we should expect to see more extreme rain events, even in areas where overall precipitation is projected to decrease. In other words, when it rains, it will likely pour.
The map shows percent increases in the amount of precipitation falling in very heavy events from 1958 to 2012 for each region of the continental United States. These trends are larger than natural variations for the Northeast, Midwest, Puerto Rico, Southeast, Great Plains, and Alaska. The trends are not larger than natural variations for the Southwest, Hawai‘i, and the Northwest. Credit: 2014 US National Climate Assessment
The latest round of UN climate change talks is currently underway in Lima, Peru. Representatives from nearly 190 countries are meeting to discuss ways to reduce greenhouse gas emissions, the main driver of global warming.
Earth’s atmosphere is made up of a variety of gases, mostly nitrogen and oxygen by volume. The greenhouse gases, including water vapor, carbon dioxide, and methane, represent a smaller percentage, but are also a natural part of the mix. Acting like the windowpanes of a traditional glass greenhouse, these gases allow the sun’s energy (shortwave radiation) to pass through the atmosphere during the day and heat the Earth’s surface. At night, the greenhouse gases trap some of the heat (long-wave radiation) that the surface emits as it cools. In essence, greenhouse gases function like a blanket that help keep the planet warm. Without them, the average surface temperature of the Earth would be 0°F – a temperature at which all the water on the planet would be frozen and life as we know it would not exist. Having too many greenhouse gases is also a problem – one that we are currently facing.
Simply put, more greenhouse gases in the atmosphere trap more heat and increase the planet’s average temperature. During the last century, according to the IPCC, Earth’s mean temperature rose 1.5°F. As temperatures continue to rise, long established weather patterns and storm tracks are shifting. Different regions, in turn, are being affected in different ways. Some areas are getting wetter, while others are getting dryer, and coastal communities are feeling the impacts of rising sea levels.
Scientists say that while some greenhouse gases come from natural sources like volcanic eruptions, the vast majority entering our atmosphere today come from human activities that burn fossil fuels. Before the industrial revolution in the late 1700’s, atmospheric carbon dioxide levels were 280 parts-per-million (ppm). This year, it passed 400ppm for the first time in human history. In addition, according to NOAA, 2014 is on track to be the planet’s warmest year on record.
Any agreements reached in Lima on reducing greenhouse gas emissions will be used as the framework for a binding global treaty at the UN Climate Conference in Paris next year.
Source: dec.ny.gov
The UN’s Intergovernmental Panel on Climate Change (IPCC) released the final installment of its massive fifth assessment report on Sunday. It synthesizes the reports from each of its three working groups – physical science, impacts and vulnerabilities, and mitigation.
Here are some the key findings:
This synthesis report will be used as a guide for the policy makers attending the UN Global Climate Summit scheduled for December 2015 in Paris. Any treaty agreed to there will take effect in 2020.
Flash! Bang! Thunderstorms are impressive displays of the power of nature. But how, you may wonder, do lightning and thunder form?
First comes the lightning, an intense electrical discharge. While not completely understood, it is believed to form as a result of the separation of charges within a cumulonimbus cloud. One theory of how this happens involves the collision of particles within these towering clouds, including hailstones, super-cooled liquid water droplets, and ice crystals. When they mix and collide, according to NOAA, “electrons are sheared off the ascending particles and collect on the descending particles.” This results in a cloud with a negatively charged base and a positively charged top.
As the atmosphere is a good insulator, generally inhibiting the flow of electricity, the strength of this electrical field has to build up substantially before lightning can occur. Most discharges, about 75%, occur across the electrical field within the storm cloud itself. This is known as intra-cloud lightning.
Another electrical field can also develop below the cloud. Since the cloud base is negatively charged, it induces a positive charge on the ground below, especially in tall objects such as buildings and trees. When the charge separation becomes large enough, a negatively charged stepped leader – an invisible channel of ionized air, moves down from the base of the cloud. When it meets a channel of positive charges reaching up from the ground, known as a streamer, a visible flash of lightning can be seen. This is called cloud to ground lightning.
Lightning can be as hot as 54,000°F, a temperature that is five times hotter than the surface of the sun. When it occurs, it heats the air around it in a fraction of a second, creating an acoustic shock wave. This is thunder. A nearby lightning strike will produce thunder that sounds like a sharp crack. Thunder from a distant storm will sound more like a continuous rumble.
While thunderstorms can be spectacular events to watch, they are also very dangerous. So, as the National Weather Service recommends, “When thunder roars, go indoors.”
Credit: NWS
Thunderstorms are fairly common in the late spring and summer in the United States. Every once in a while, though, they can be severe. When they are, the sky often turns green. You may wonder, what causes this odd coloration?
According to scientists, the phenomenon of green skies is not completely understood. The leading theory, however, involves the dense moisture content of cumulonimbus clouds and the time of day. Most thunderstorms develop in the late afternoon, a time when the sun’s rays have to travel a long way through the atmosphere before reaching the ground. This causes the light we see around sunset to be reddish-yellow. Thunderstorm clouds contain large amounts of rain and hail. This water and ice scatters blue light. So, when these towering clouds form in the late afternoon, the two colors mix to give the sky a green or blue-green appearance.
While severe thunderstorms can produce tornadoes, a green sky does not necessarily mean a twister is coming. Nonetheless, the color is associated with dangerous weather. If you see a thunderstorm heading your direction and the sky appears green, you should seek shelter immediately.
Green Sky. Image Credit: Sky7WX