GLOBAL WARMING - LAND PRECIPITATION DON'T FORGET TO ADD A COMMENT AT THE END OR GO THE BOTTOM OF THE SCREEN TO SEE WHAT OTHERS HAVE WRITTEN |
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NOAA - Land-based precipitation (MUST CONFIRM WITH DATA) |
Globally-averaged land-based precipitation shows a statistically insignificant upward trend with most of the increase occurring in the first half of the 20th century. Further, precipitation changes have been spatially variable over the last century. On a regional basis increases in annual precipitation have occurred in the higher latitudes of the Northern Hemisphere and southern South America and northern Australia. Decreases have occurred in the tropical region of Africa, and southern Asia. Due to the difficulty in measuring precipitation, it has been important to constrain these observations by analyzing other related variables. The measured changes in precipitation are consistent with observed changes in stream flow, lake levels, and soil moisture (where data are available and have been analyzed). |
Clouds are also an important indicator of climate change. Surface-based observations of cloud cover suggest increases in total cloud cover over many continental regions. This increase since 1950 is consistent with regional increases in precipitation for the same period. However, global analyses of cloud cover over land for the 1976-2003 period show little change. | NOAA - Clouds indicate climate change. (MUST CONFIRM WITH DATA) |
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NOAA - Snow cover below the average since 1987. (MUST CONFIRM WITH DATA) |
Northern Hemisphere snow cover extent has consistently remained below average since 1987, and has decreased by about 10% since 1966. This is mostly due to a decrease in spring and summer snow extent over both the Eurasian and North American continents since the mid-1980s. Winter and autumn snow cover extent have shown no significant trend for the northern hemisphere over the same period. |
The National Weather Service is projecting this year's spring runoff into Lake Powell will be 122 percent of average. That will raise Lake Powell, currently at elevation 3591 feet above mean sea level, approximately 50 feet by mid-July, to its highest elevation in six years. Powell is currently projected to end the calendar year almost 40 feet higher than it is today. For the past seven years, the annual release from Lake Powell to Lake Mead has been 8.23 million acre-feet. Based on the April 1 inflow forecast, Reclamation projected that, by the end of September, Lake Powell would rise above 3636 feet above mean sea level (msl) and Lake Mead would be below 1105 feet msl. In accordance with the interim guidelines, an additional amount of water will therefore be released from Lake Powell to Lake Mead for water year 2008 (Oct. 1, 2007 - September 30, 2008). |
U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF RECLAMATION - High Snowpack Triggers Additional Releases from Lake Powell to Lake Mead in Accordance with New Guidelines (FACTS - Amounts of Snowpack, THEORY - Not quite sure how much the lake will raise) |
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NOAA - Increase in droughts and excessive wetness. (MUST CONFIRM WITH DATA) |
In areas where a drought or excessive wetness usually accompanies an El Niño or La Niña, these dry or wet spells have been more intense in recent years. Further, there is some evidence for increasing drought worldwide, however in the U.S. there is no evidence for increasing drought.In some areas where overall precipitation has increased (ie. the mid-high northern latitudes), there is evidence of increases in the heavy and extreme precipitation events. Even in areas such as eastern Asia, it has been found that extreme precipitation events have increased despite total precipitation remaining constant or even decreasing somewhat. This is related to a decrease in the frequency of precipitation in this region. | The satellite was only launched in 2002 and it enabled the collection of data, not just on temperature but also on cloud formation and water vapour. What all the climate models suggest is that, when you've got warming from additional carbon dioxide, this will result in increased water vapour, so you're going to get a positive feedback. That's what the models have been indicating. What this great data from the NASA Aqua satellite ... (is) actually showing is just the opposite, that with a little bit of warming, weather processes are compensating, so they're actually limiting the greenhouse effect and you're getting a negative rather than a positive feedback." | Institute of Public Affairs from The Australian - "The temperature of the earth has been decreasing over the last 10 years." (MUST CONFIRM WITH DATA) |
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NOAA - Clouds indicate climate change. (MUST CONFIRM WITH DATA) |
Clouds are also an important indicator of climate change. Surface-based observations of cloud cover suggest increases in total cloud cover over many continental regions. This increase since 1950 is consistent with regional increases in precipitation for the same period. However, global analyses of cloud cover over land for the 1976-2003 period show little change. |
Major floods striking America’s heartland in March offer a preview of the spring seasonal outlook, according to NOAA’s National Weather Service. Several factors will contribute to above-average flood conditions, including record rainfall in some states and snow packs, which are melting and causing rivers and streams to crest over their banks. The week of March 15, more than 250 communities in a dozen states are experiencing flood conditions. | SCIENCE DAILY - Current Major Flooding In U.S. A Sign Of Things To Come, NOAA Predicts | ||||||||
NOAA - Precipitation is expected to increase. (MUST CONFIRM WITH DATA) |
Precipitation is also expected to increase over the 21st century, particularly at northern mid-high latitudes, though the trends may be more variable in the tropics, with much of the increase coming in more frequent heavy rainfall events. However, over mid-continental areas summer-drying is expected due to increased evaporation with increased temperatures, resulting in an increased tendency for drought in those regions. |
The National Weather Service is projecting this year's spring runoff into Lake Powell will be 122 percent of average. That will raise Lake Powell, currently at elevation 3591 feet above mean sea level, approximately 50 feet by mid-July, to its highest elevation in six years. Powell is currently projected to end the calendar year almost 40 feet higher than it is today. For the past seven years, the annual release from Lake Powell to Lake Mead has been 8.23 million acre-feet. Based on the April 1 inflow forecast, Reclamation projected that, by the end of September, Lake Powell would rise above 3636 feet above mean sea level (msl) and Lake Mead would be below 1105 feet msl. In accordance with the interim guidelines, an additional amount of water will therefore be released from Lake Powell to Lake Mead for water year 2008 (Oct. 1, 2007 - September 30, 2008). |
U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF RECLAMATION - High Snowpack Triggers Additional Releases from Lake Powell to Lake Mead in Accordance with New Guidelines (FACTS - Amounts of Snowpack, THEORY - Not quite sure how much the lake will raise) |
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NOAA - Snow and sea-ice is projected to decrease. (CONFLICT - DISPROVEN BY DATA) |
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UCAR - THE UNIVERSITY CORPORATION FOR ATMOSPHERIC RESEARCH - Drought's Growing Reach: (MUST CONFIRM WITH DATA) |
BOULDER- The percentage of Earth's land area stricken by serious drought more than doubled from the 1970s to the early 2000s, according to a new analysis by scientists at the National Center for Atmospheric Research (NCAR). Widespread drying occurred over much of Europe and Asia, Canada, western and southern Africa, and eastern Australia. Rising global temperatures appear to be a major factor, says NCAR's Aiguo Dai, lead author of the study. Dai will present the new findings on January 12 at the American Meteorological Society's annual meeting in San Diego. The work also appears in the December issue of the Journal of Hydrometeorology in a paper also authored by NCAR's Kevin Trenberth and Taotao Qian. The study was supported by the National Science Foundation, NCAR's primary sponsor. Dai and colleagues found that the fraction of global land experiencing very dry conditions (defined as -3 or less on the Palmer Drought Severity Index) rose from about 10-15% in the early 1970s to about 30% by 2002. Almost half of that change is due to rising temperatures rather than decreases in rainfall or snowfall, according to Dai. "Global climate models predict increased drying over most land areas during their warm season, as carbon dioxide and other greenhouse gases increase," says Dai. "Our analyses suggest that this drying may have already begun." |
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| The satellite was only launched in 2002 and it enabled the collection of data, not just on temperature but also on cloud formation and water vapour. What all the climate models suggest is that, when you've got warming from additional carbon dioxide, this will result in increased water vapour, so you're going to get a positive feedback. That's what the models have been indicating. What this great data from the NASA Aqua satellite ... (is) actually showing is just the opposite, that with a little bit of warming, weather processes are compensating, so they're actually limiting the greenhouse effect and you're getting a negative rather than a positive feedback." | Institute of Public Affairs from The Australian - "The temperature of the earth has been decreasing over the last 10 years." (MUST CONFIRM WITH DATA) |
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Consequence: drought and wildfire
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Carbon Dioxide Information Analysis Center - Short lesson on heating your environment with precipitation. (FACT - Natural Process) |
Absolute humidity refers to the amount of water vapor actually in the air, which can be higher than 2% of the atmosphere's mass if it's very warm, but is limited to around 0.1% or less of the atmosphere's mass if it's colder than about zero degrees Fahrenheit. Relative humidity is the amount of water vapor actually in the air expressed as a percentage of the amount that could be there (at a given temperature) given the amount of heat the atmosphere has available to maintain water molecules in the vapor state (i.e., without condensing to liquid water). At low temperatures, the air can't maintain much water in the vapor state, but at high temperatures it can. (In hot, dry, weather, sweat evaporates faster because the surrounding air contains a lot less water vapor than it can maintain.) Over a desert, the absolute humidity can be pretty high (e.g., in the Middle East, near the Mediterranean Sea), but the associated high temperatures typically allow much more water to be maintained in the vapor state than there actually is, so the relative humidity is typically low (but not always, fog occurs over coastal deserts, but that's another subject). Clouds absorb a lot of outgoing (infrared) radiation, and re-radiate it in all directions including back down to earth. On nights when clouds are sparse or nonexistent, much less radiation comes back to us and more goes through the atmosphere out to space. This explains the large amount of radiative cooling at night in deserts, where clouds are sparse or nonexistent even though the ABSOLUTE humidity can be high. On clear, cold, winter nights, the lack of clouds is complimented by a low amount water vapor actually in the air (because it's cold, not much vapor can be there), so that the amount of outgoing infrared radiation absorbed by the atmosphere is reduced, and more escapes to space. In both cases, the increased nighttime cooling increases the daily temperature range. Also, in many deserts, the thermal conductivity of the (dry) soil is really small, especially in a sandy desert where the soil particles are relatively large and there is a lot of space for air in between. This means that less heat is transported to, and stored in, the soil during the day. When you visit the beach, you may notice that the surface sand is hot while an inch below the surface it is much cooler (nothing like the Tennessee clay in my backyard). When the sun goes down, that hot surface is radiating a lot of energy away very quickly and there isn't much heat in the subsurface "bank" to draw on. The result is some pretty low surface temperatures in the wee hours of the morning. In summary, the reduced thermal inertia near the desert surface explains the wider variations in temperature, as compared to an agricultural area, for example. Also, the dew point is a big influence on minimum temperatures. Once the dew point is reached, the conversion of water molecules from gas to a liquid releases a bunch of heat (ca. 2500 J/g)* which tends to keep the temperature from falling further. In deserts, even though the ABSOLUTE humidity might be pretty high (on a really hot day), the RELATIVE humidity tends to be low, so that the air can cool a lot before the dew point is reached. This allows greater cooling at night. On the clear winter nights the air is usually dry to begin with (after all, no clouds were formed) so, it can cool off a lot before getting to the dew point (or, to the frost point). * If you lick your hand and blow in it you will notice that your skin cools off. In the same way evaporation of sweat cools me off during the warm afternoon that I am refereeing a soccer match, and panting can help even more (that's how dogs keep cool). What is happening is that a lot of energy is required to get the water molecules from the liquid state to the much more energetic gaseous state, and that (heat) energy comes from the surface from which the molecule is evaporated (e.g., your skin). When the reverse happens (vapor condenses to liquid) the molecules lose energy, which is realized as heat. More water vapor can coexist with warm air than with cold air; in warm air, more heat energy is available to maintain the water molecules in their (more energetic) gaseous state. If the air cools, then some energy will be lost by the water molecules and some of them will revert to the liquid state. [TJB] |
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