This week's science question is - Which of the following is true?

--The world's lowest temperature (excluding Antarctic) has never occurred in Africa.

--The low temperature for a given day in the US has occurred at a location further south than the nation's highest temperature.

--The US is the only country that has recorded the world's highest temperature and lowest temperature (excluding Antarctica) on the same day.

In regards to the above questions, the answers below refer to published temperature data from reliable meteorological stations. However, on any given day, it's likely that a more extreme temperature occurred some place in the world. In addition, some countries don't always make their data readily available to climate networks.

The world's lowest temperature (excluding Antarctic) has never occurred in Africa.

When most of us picture Africa, we might conjure up images of jungles in the Congo, deserts like the Sahara, or savannas like the Serengeti. Since the African continent pretty much straddles the Equator, cold temperature and snow aren't usually associated with Africa. However, the Atlas Mountains in northern Africa are snow covered each winter, and of course, Hemingway made the snows of Kilimanjaro famous.

The Atlas Mountains rise to as high as 12, 912 feet (4,165 m) and reach a latitude of almost 36 degrees north, which is similar to the elevation and latitude of the highest peak in Arizona, Mt. Humphrey. Accumulating snow and subsequent snowmelt in the spring is an important resource to people living in the parched landscape at the base of the Atlas Mountains. Mt. Kilimanjaro looms over the African plains, and even though it's fairly close to the Equator (about 3 degrees south latitude), at an elevation over 18,000 feet (5,895 m), it's able to support glaciers. It should be noted, thought, that the Kiliamanjaro glaciers are rapidly diminishing in size, an by 2020 may be a thing of the past. The shrinking ice fields might be related to warming, which has also been observed over ice fields in the Andes Mountains and other tropical mountains.

Because there are few villages or towns located in the high Atlas Mountains, on the flanks of Kilimanjaro, or other high volcanic peaks in the African Rift Zone, the lowest temperatures in Africa typically occur far to the south. In fact, it can snow in southern Africa, despite elevations that are shy of those found in the Atlas Mountains and a southernmost latitude only about 35 degrees from the Equator. Nevertheless, during the winter months (June through August), snow can fall in the higher elevations, inland from the coast, and temperatures can dip well below freezing. This past July, a surprise snowstorm near Johannesburg, South Africa dumped more than 6 inches of snow (about 8 cm), and on July 15 in the town of Shaleburn, South Africa the temperature dropped to 22 degrees F (-6 degrees C). It just so happened that this was the lowest temperature recorded anywhere in the world on that day, excluding Antarctica. Thus, the answer to the question above is False.

A couple of weeks before this, the temperature on June 28 in Sutherland, South Africa dipped down to 13 degrees (- 11 C), also the world's minimum temperature for this day. Sutherland is about 200 miles (320 km) northeast of Capetown and is known for its brilliant night skies and cold winters - it's situated on the Roggeveld Plateau, nearly 5,000 feet (1,613 m) above sea level. It's also the home of the South African Astronomical Observatory. Low rainfall and unpolluted air ensure maximum nighttime visibility and radiational cooling. At about 33 degrees south latitude, Sutherland seems too close to the Equator to be able to lay claim to any lowest temperature records, but since the Sun is up nearly all day across the northern latitudes of the Northern Hemisphere during much of June, July and August, and because southern South America is often cloudy, on occasion the Earth's minimum temperature can occur in Africa.

The low temperature for a given day in the US has occurred at a location further south than the nation's highest temperature.

In the US, most of the time but not always, our nation's highest temperatures are found in the southern states, particularly in the desert southwest, and the coldest temperatures occur in Alaska or across the northern tier of states. If it's hot in the Great Plains of Kansas, Nebraska or the Dakotas, it's hotter in Oklahoma, Texas or in the desert areas of Arizona, California, and Nevada. Similarly, if it's chilly in Kentucky or Tennessee, it's bound to be colder in Minnesota or Michigan. However, on rare occasions, our nation's lowest daily reading (outside of Alaska) has occurred in a southern state and when this happens, it's possible that the station recording this minimum temperature is actually south of the location of where the maximum temperature for the day was observed. For example, on May 14 of this year, the high temperature in the US was 105 degrees (42 C) in Death Valley, California (no surprise), and the low was 16 degrees (-9 C) at Happy Jack, Arizona, about 2 degrees of latitude south of Death Valley. The answer to the above question is therefore True.

For a US low temperature to occur this far south (35 north latitude), several things have to happen simultaneously. The season must be late spring or summer, it has to be cloudy in portions of the northern US (the presence of clouds precludes optimal radiational cooling), it has to be clear and dry over Arizona (not unusual for Arizona in May or June), and most importantly, the temperature sensor has to be located several thousand feet above sea level. In fact, Happy Jack is 7,458 feet (2,406 m) above sea level. Indeed, it's hard to imagine that our nation's minimum for any given day could occur at a populated site any further south than this. Even if Alaska is included, it's not out of the question that the nation's minimum temperature could occur south of where the high occurred. This could only happen in mid summer when most of Alaska is exposed to prolonged periods of daylight. At 70 degrees north latitude, the minimum temperature will remain above freezing in mid summer - as long as there's no snow on the ground.

The US is the only country that has recorded the world's highest temperature and lowest temperature (excluding Antarctica) on the same day.

Not only the size, but the shape and position of a particular country (in regards to extremes of solar radiation) play a role in determining how hot and cold the temperature may become. In general, the more elongated or north-to-south the country, the greater the temperature spread. For instance, Chile and Argentina are two of the most elongated countries, and temperatures vary considerably between their northernmost and southernmost towns. The northern portions of both of these countries are equatorward of the Tropic of Capricorn, while the southern portions extend to 55 degrees south latitude. In the case of Chile, there's almost 37 degrees of latitude difference between the northern border and the tip of Tierra Del Fuego! The contiguous US, which is considerably larger than Chile, is by contrast much more compact, extending only about 25 degrees in latitude. But because all of Chile lies within about 100 miles (160 km) or so of the Pacific Ocean, it doesn't experience the same sort of temperature extremes that it would if it were sandwiched in the middle of a continent. Argentina, on the other hand, isn't as skinny as its western neighbor, and its northern interior is far enough from the Atlantic and Pacific Oceans to sizzle in summer and freeze in winter. It's continentality is higher than Chile's. The world's maximum and minimum temperatures have been recorded in Argentina but never on the same day. During the Southern Hemisphere winter (our summer), the world's minimum temperature, again excluding Antarctica, occurs quite often in Argentina, but it's then too chilly, even at 23 degrees south latitude, to really heat up.

Norway and Sweden are also very elongated, and daily world minimums are sometimes recorded in Scandinavian towns north of the Arctic Circle, but they're both positioned too far north to compete for the world's maximum temperatures. Likewise, a number of other countries that have a fairly extensive north to south range are positioned too close to the Equator, such as India or Mozambique, to have much of a chance to record a daily minimum records. This being said, if elevations are sufficiently high, as is the case with Bolivia and Peru, a worldwide minimum temperature can occur between the Tropic of Cancer and the Tropic of Capricorn.

Russia is elongated or stretched out in an east-west direction, covering 11 time zones. Before the Soviet Union broke apart in 1991, Russia extended further to the south than it does now. The Kyzyl Kum desert region in what is now Turkmenistan and Uzbekistan, in south central Asia, can be brutally hot during the summer, and in year's past, it's possible that a daily global high temperature was recorded in the Kyzyl Kum while on the same day, a global minimum was being recorded in distant Siberia. However, Russia now lies too far poleward to record a daily global high temperature. This is probably the case for Canada as well.

China and the US are both big enough and favorably positioned in the mid latitudes to record global maximum and global minimum temperatures on a given day. China has even a greater latitude range than does the contiguous US, but the Gobi Desert in north central China and the Taklimakan Desert in far western China don't get as hot as the Sonoran Desert or Mohave Desert in the southwestern US. This is so because the Taklimakan and Gobi are high elevation deserts, and because they receive less solar radiation at the surface than do deserts in the southwestern US, northern Africa or the Arabian Peninsula. Thus world daily maximum temperatures are rarely recorded in China.

The US is the only country to have part of its national boundaries equatorward of the Tropic of Cancer or Capricorn and poleward of the Arctic or Antarctic Circle. Only during the summer months, though, is there a possibility that the US could record the world's highest temperature and lowest temperature on the very same day. This happened most recently on August 17, 2002; the global maximum temperature was 122 degrees (51 C) at Death Valley, and the global minimum was 20 degrees (-7 C) at Wisdom, Montana (located in the southwestern part of the state). So the answer to the above question is probably True.

This feat almost happened again a few weeks later. On the morning of September 5, 2002, Bodie State Park, California dropped to 12 degrees (-12 C,) which was the coldest spot on the globe, with the exception of Antarctica. However, Al Hofuf, Saudi Arabia (115 degrees or 47 C) just edged out Bullhead City, Arizona (113 degrees or 46 C) for the global hot spot. The temperature difference between Bodie State Park and Bullhead City was a staggering 101 degrees (there was approximately a 10 hour difference between the time these temperatures were recorded), and the distance separating them is less than 400 miles (640 km)!

In summary, not only does latitude impose a restraint on temperature, but altitude, the amount of solar radiation reaching the ground, cloudiness, the size of a land mass, surface albedo, and topography are all important in determining how hot or cold a given location may become. For more about temperature extremes, see the Science Question of the Week for January 17, 2002 and May 23, 2002.