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Table of Contents


Characteristics of the Atmosphere


The Global Climate





Physical Geography

Characteristics of The Atmosphere













Physical Geography

WeatherWeather Cartoon

How to Read Weather Maps (5:15)

Weather Forecasting: Air Masses and Fronts (12:33)














The Hydrological Cycle




The Köppen Climate Classification System




Heating and Cooling




Temperature Patterns

What Is the Polar Vortex?




Localized Wind Systems










Low-lying clouds cover valleys between peaks in the Austrian Alps












Air Masses








Atmospheric Disturbances



A tornado forms at sunset.



























Antarctica's ozone hole

Physical Geography

The Global Climate

Global Warming and The Greenhouse Effect


The National Climate Assessment




El Niño

Periodic warming of the Pacific Ocean has occurred for thousands of years but only recently have scientists come to appreciate its global reach. In its simplest sense, ElEl Nino and weather Nino's effects are like placing a large stone in a shallow river. It causes ripples that run far downstream. Normally, the hottest ocean surface temperatures on the planet are found in the western Pacific, near Indonesia. During an El Nino, however, these warm, rain-generating waters slide east, creating conditions for large storms. This can also alter the path of powerful jet stream currents high above the Earth, disrupting seasonal weather patterns in profound ways. In parts of North and South America, a succession of pounding storms can roll over the landscape, as if delivered by an atmospheric conveyor belt. Seasonal rains can fail to arrive in parts of India, Africa and Southeast Asia, killing crops and stoking wildfires.

Drought causes other dangers as well. In Indonesia, slash-and-burn clearing of agricultural land has given rise to rampant forest fires. These massive fires, which have occurred during every El Nino since 1982, sicken hundreds of thousands of people. The smoke, which often spreads to Malaysia, Singapore, the Philippines and Thailand, also releases enormous quantities of the greenhouse gas carbon dioxide. El Nino-inspired drought or flooding can have other health effects: Outbreaks of cholera, typhoid and other diarrheal diseases occur in areas where flood waters have been contaminated by human or animal feces.

Warming Pacific waters can generate an increase in hurricanes and El Nino was cited as a possible factor in the creation of Hurricane Patricia, one of the strongest hurricanes ever recorded. Warm water is kind of rocket fuel for hurricanes. Similarly, researchers cite the warming effects of El Nino as a factor in recently declared global coral bleaching events. Temperature change is one of several factors that can cause coral reefs to lose their coating of algae, turning them white and endangering their survival. El Nino's effect on fisheries gave it its unique name. Before it was understood to be a global event, fishermen in Peru and Ecuador used the term to describe the warm currents that sometimes arrived around Christmas time and seemed to drive fish away. El Nino, Spanish for "the child," was a reference to the birth of Christ.

Normally, trade winds that blow from east to west cause an upwelling of deep, cold, nutrient-rich water along the coast of South America. This cool water sustains fish like anchovies, which are used internationally to feed livestock. During El Nino, however, the trade winds slow, or collapse entirely, putting an end to the upwelling — and the anchovy fisheries. This not only affects Peruvian fishermen but also sends shock waves through the commodities market as the price for soybeans — another source of livestock feed — rises. It starts a chain reaction around the globe.


In the central Pacific, a record 14 named tropical storms or hurricanes have spun through the region in the 2015 season. Fortunately, as is the case with most Pacific hurricanes, few have hit land.

El Niño, a natural warming of tropical Pacific Ocean waters, has provided fuel for the storms, which usually need warm water of at least 80º to form. Ocean temperatures near Hawaii are at record highs. El Niño also reduces the winds that tend to tear hurricanes and typhoons apart.

Other than Hurricane Joaquin, the Atlantic hurricane season has been mostly a dud, as predicted and as is typical during El Niño. Only three hurricanes have formed, according to the National Hurricane Center.

As for global warming, would warmer oceans would mean that stronger, more frequent hurricanes like Patricia are possible? The jury is still out on that one. It is premature to conclude that human activities — and particularly the greenhouse gas emissions that cause global warming — have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. (Tropical cyclones are all tropical storms, hurricanes and typhoons.)

However, looking ahead, warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average. Scientists are always clear to point out that no one storm can be blamed on or caused by man-made climate change. All weather events are due to many causes, such as El Niño.



Global Climate Change


Climate Shift




a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years)








The Historic Paris Climate Deal

In December 2015, negotiators from 196 countries approved a climate accord to curb the rapid growth of greenhouse gases and prevent a dangerous warming of the planet. Here are the main elements, based on the latest text:

The temperature target: The nations of the world will try to limit “the increase in the global average temperature to well below 2° C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5° C above pre-industrial levels.” The language represents a huge win for small island states and other developing nations that argue a temperature increase above 1.5 degrees would be devastating for them.

How countries will get there: The countries that signed the agreement pledged to “reach global peaking of greenhouse gas emissions as soon as possible,” but the text doesn’t specify a date. It says the parties to the pact will “undertake rapid reductions thereafter in accordance with best available science, so as to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century.”

This doesn’t mean emissions would go to zero. It means they would go low enough to be off-set by natural processes or advanced technologies that are able to remove greenhouse gases from the air.

The next steps: The text pledges all countries to delivering, every five years, a new national pledge to reduce emissions. Each pledge, it says, should represent a “progression” over the prior one, and should reflect the country’s “highest possible ambition.” Climate watchers see this process as crucial, because current country pledges aren’t strong enough to limit warming to below 2° C much less 1.5° C.

Adapting to the changes that are already coming: The text states that countries will “engage in adaptation planning processes” to ensure that they’re ready for the effects of climate change. For impacts that cannot be adapted to, the proposed accord contains a “loss and damage” section, suggesting that these cases will be addressed through a variety of means including “risk insurance facilities, climate risk pooling and other insurance solutions.” This provision is another key win for small island states and other developing, vulnerable nations.

Who pays? The long-contested section on climate finance says that developed countries, like the US, “shall provide financial resources to assist developing countries with respect to both mitigation and adaptation” – in other words, helping them brace for impacts but also to transition to cleaner energy systems. The text suggests, though, that wealthier developing countries can contribute such funds if they would like. Developed countries would have to communicate about their climate donations every two years.

The Great Thaw

Gauging a Warming World (Interactive Graphic)

The Invisible Threat: Rising temperatures mean insects can carry viruses to wider areas.

That’s Heavy: Climate-change warnings include rising seas and wild weather shifts.

The Magic Number: Holding warming under two degrees Celsius is the goal. But is it still attainable?


Climate Risks: 1.5C vs 2C Global Warming

Arctic Ice Melt 

Watch the Last 28 Years of Arctic Ice Melt



Indicators of a Warming World








Copyright © 1996 Amy S Glenn
Last updated:   04/06/2024 0600

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