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At the tropopause (the point in altitude where the lowest part of Earth’s atmosphere, the turbulent troposphere, transitions into the more stable stratosphere), which is located at about nine miles up, bands of 200 mile-per-hour air currents flow around the world while periodically meandering north and south. These air currents are known as jet streams. [...]

In Southeast Arizona, there has been a marked increase in wintertime rainfall since 1977, which has resulted in a three-fold increase in shrub cover. Prior to this period, grasses had dominated the region’s vegetation system. As the shrubs have moved in, so have species of small pocket-mice, which are replacing large kangaroo rats. One species [...]

In northern Québec, patches of Black Spruce forests exist alongside the arctic shrub tundra, forming an ecological zone known as forest-tundra. Heavy winter snows, short frost-free growing seasons, and high winds limit the possible area in which Black Spruce trees can grow. These harsh conditions also limit how tall these trees can grow, and in [...]

A warmer atmosphere results in an “amplification” of the water cycle. Some areas of the world are net importers of rainfall (such as tropical rainforests), while some are net exporters (such as oceans around the tropics). The “amplification” of the cycle means that dry regions become drier, and wet regions become wetter. During the 20th [...]

Temperatures in the East African Highlands have risen by about one degree Fahrenheit over the past 50 years. This area includes Uganda’s Rwenzori Mountains, which feature glaciers that supply the lowland plains region with water. Between 1987 and 2003, the area covered by glaciers in these mountains shrunk by about 50 percent. This retreat has [...]

Autumn (March to May) rainfall in southeast Australia is important for soil moisture and river recharge because the region is dependent on reliable water sources for cereal crop production. Since 1950, there has been a 40 percent decline in the region’s average autumn rainfall. This has been linked to fewer occurrences of La Niña events, [...]

Did you know that 75 percent of the water resources in the West originate from snowmelt? Mountain snowpack accumulates over the winter and as it melts during the spring, summer, and fall, it feeds the region’s rivers and streams. Over the last half of the 20th Century, November to March temperatures in the Pacific Northwest [...]

A warmer atmosphere results in an “amplification” of the water cycle. Some areas of the world are net importers of rainfall (such as tropical rainforests), while some are net exporters (such as oceans around the tropics). The “amplification” of the cycle means that dry regions become drier, and wet regions become wetter. During the 20th [...]

Is it possible for droughts to become more common even if annual rainfall amounts increase? Overall annual precipitation in the lower 48 states has been increasing since the early 20th century, and since the 1970’s it has been increasing in the Eastern United States by about one-inch per decade. Over the last forty years, this [...]

Geysers are hot springs that intermittently discharge fountains of steaming hot water through conduits running from shallow reservoirs of groundwater to the surface. These groundwater reservoirs are heated by the planet’s magma, and when the temperature in the geyser conduits exceeds the boiling point, a stream of liquid and gas comes shooting out of the [...]

In the Pacific Northwest, Mountain Hemlocks grow at elevations between 3,600 and 7,500 feet. These shade tolerant trees grow underneath the faster growing but shorter-lived Douglas Firs, and gradually make their way to the top of the canopy over their 700 year life spans. At the region’s high elevations, some of the world’s most extensive [...]

Tropical rainforests are inhabited by more plants and animals than any other place on Earth. These plants and animals are accustomed to hot temperatures and abundant rainfall throughout the year. Globally, rainfall in tropical rainforests has been decreasing since 1960 at a rate of one percent per decade. Most of the decline during this period, [...]

The northeastern quadrant of the contiguous United States, defined as the area from Minnesota south to Missouri and then east to Maryland and north to Maine, has been experiencing changes in its precipitation regime. While the average annual number of “wet” days (or days when rain falls) in that region declined by about four percent [...]

While cold temperatures limit growth for many plant species inhabiting the boreal forest and tundra regions of the northern hemisphere (from about 50 to 80 degrees North), increases in temperature can cause more evaporation from the soil and lead to drought stress. This appears to be the case with White Spruce forests in Alaska. A [...]

Convective available potential energy (CAPE) is a measure of how much energy is available for storm development (CAPE is measured by the number of joules present in a kilogram of air). Generally, the hotter and more humid conditions are, the more CAPE is present. A collection of atmospheric conditions, including some CAPE, are necessary for [...]

Eighty-three (83) percent of the moisture entering tropical Africa originates in the Indian Ocean. Over the last four decades of the 20th century, sea surface temperatures (SSTs) in the tropical Indian Ocean rose by nearly two degrees Fahrenheit, making these waters the warmest they have been in 120,000 years. As this has happened, rainfall over [...]

The Arctic Ocean is surrounded by a series of river drainage basins, which collectively occupy an area 1.5 times that of the ocean basin itself. No other ocean basin’s temperature and salinity levels are more dependent on what happens on the adjacent land surface. These temperature and salinity levels in turn influence the behavior of [...]

Southern California’s Santa Rosa Mountains, located about two hours southeast of Los Angeles, stand out as forest islands amongst the lowland desert to the east, and the chaparral scrubland to the west. Plants not capable of tolerating the hot and dry conditions of the lowlands find refuge at the cooler and wetter high elevations. Over [...]

About 7,700 years ago, a volcanic eruption 42 times more powerful than the 1980 Mt. St. Helens event happened at Mt. Mazama in the southern Oregon Cascade Mountains. The top 5,000 feet of the mountain collapsed soon afterwards, leaving behind a huge caldera, or crater, which has since filled with about 4.6 trillion gallons of [...]

The El Niño-Southern Oscillation (ENSO), or the cyclical movement of heat in the tropical Pacific Ocean, affects atmospheric phenomena throughout the world. The cycle affects the strength and position of the Pacific Jet Stream, an upper atmosphere wind current that flows from the Pacific over North America. During La Niña phases of the cycle, the [...]