Walt Kelly, the originator of Pogo, didn’t know about global warming, but the sentiment fits.

Water supplies and global warming. Water supplies are already limiting many human societies. Shortages are likely to become increasingly frequent as global warming interacts with growing populations and increasingly developed societies that demand more water for agriculture, manufacturing, and personal use. Global warming is likely to increase these problems by increasing the frequency of both floods and droughts and changing the seasonal pattern of runoff from snowpacks and glaciers. In addition, salt water incursion into low lying coastal areas and river deltas will restrict agriculture, reduce availability of fresh water, and endanger fresh water wildlife. Water pollution is also a major problem. More than five million people die from waterborne diseases each year - 10 times the number killed in wars around the globe.

The amount of water on Earth is fixed. Less than 0.01% of the planet's 1.4 billion cubic kilometers is easily accessible freshwater in lakes and rivers. About a fifth of the water used worldwide comes from the 30% of the world's freshwater which is stored in groundwater.

The world's population has tripled in the last 100 years, but water use has increased sixfold. Agriculture now consumes 70 % of the water used worldwide. Much more will be needed if we are to feed the world's growing population - predicted to rise from 6.8 billion today to 8.9 billion by Soaring demand

Water consumption will soar further as more people expect Western-style lifestyles and diets - one kilogram of grain-fed beef needs at least 15 cubic meters of water, while a kilo of cereals needs less than three cubic meters. Water use is very uneven. Just like energy, Americans are by far the largest consumers.

An estimated third of the world's population currently lives in water-stressed countries. This will likely increase to two-thirds within 25 years. Africa and Asia are already hard-hit by water stress. Increasing populations will create more pressure in the coming decades.

Of the many possible examples of anticipated water shortages, I’ll talk briefly about just one: the watershed of the Himalayas.

Nearly all the great rivers of Asia begin in the Tibetan Plateau

The Himalayas contain the largest store of water outside the polar ice caps, and feed seven great Asian rivers. Two billion people in the river basins depend on the Himalayan glaciers for their water supply, The rapid melting of Himalayan glaciers will first increase the volume of water in rivers by percent, causing widespread flooding. Hundreds of millions live on flood plains that are highly vulnerable to raised water levels.

There are 3,300 glaciers in the Nepalese Himalayas and 2,300 of them contain glacial lakes. These lakes are quietly growing because of rising temperatures, but nobody knows how many are close to bursting, and there are no early warning systems for the villages downstream. A glacier lake catastrophe happened once in a decade 50 years ago,' said UK geologist John Reynolds, whose company advises Nepal. 'Five years ago, they were happening every three years. By 2010 there will be one every year.' An example of the impact is provided by Luggye Tsho, in Bhutan, which burst its banks in 1994, sweeping 10 million cubic meters of water down the mountain. It struck Panukha, 50 miles away, killing 21 people. There is also the risk of sudden flash floods as rapidly expanding glacial lakes burst through their natural dams. Now a nearby lake, below the Thorthormi glacier, is in imminent danger of bursting. That could release 50 million cubic meters of water, a flood reaching to northern India 150 miles downstream.

These disruptions are quite likely to trigger major conflicts locally and internationally, as people clash over water and land. People will be forced to migrate away from their dry or flooded land. Governments will bicker over who will get the remaining water and who will pay the economic costs. But in a few decades the glaciers will be largely gone and the water level in rivers will drastically decline, meaning massive eco and environmental problems for people in China, Nepal, India, and Bangladesh. Without the glaciers, drinking and irrigation water will be drastically reduced, especially during the dry season. Crops will die. Hundreds of millions of people will be affected.

Global warming is also changing the distribution of diseases, particularly tropical diseases.

The range of Aedes aegypti, the mosquito that carries dengue fever, is limited by temperatures. Frost kills both adults and larvae. Previously, the disease could not spread out of the tropics, but rising temperatures are changing that. Dengue Fever Dengue, or "breakbone", fever is a mosquito borne disease related to yellow fever. Unlike its relative, however, there is no vaccine against dengue. One strain of the disease, hemorrhagic dengue fever, is often deadly, and doctors in the U.S. and other areas into which it is expected to spread have little experience diagnosing or treating it. It has moved steadily north in recent decades, and to higher elevations. Nepal and Bhutan saw their first cases in recent years and in South America it is climbing up the Andes. In the United States A. aegypti has reached as far north as Chicago. This means that many people who have not previously been exposed to Dengue fever virus are now at risk.

Here in the United States malaria infections are already on the rise. Houston has experienced a malaria outbreak in each of the last two years. In the last three years malaria cases have occurred as far north as New Jersey, Michigan and Queens, New York. In 1997 an outbreak occurred in Florida, striking the Disney World theme park, and mosquitoes carrying the illness were discovered in New York. Malaria Like dengue fever, malaria is a mosquito borne illness normally limited by temperatures. Rising temperatures have expanded its range, and exposed new populations to infection. IPCC scientists project that as warmer temperatures continue to spread north and south from the tropics and to higher elevations, malaria-carrying mosquitoes will spread with them. They project that global warming could put as much as 65 percent of the world’s population at risk of infection by malaria.

To make matters worse, the Asian Tiger Mosquito, Aedes albopictus, is an invasive species that has spread from its native range in Asia to all the other continents (except Antarctica). It is an aggressive daytime flier that bites rapidly, thereby avoiding most attempts to swat it. It can spread several diseases, including dengue fever and malaria.

Because it can be transmitted by the common household mosquito, Culex pipiens, West Nile virus spread rapidly after it was introduced at La Guardia airport in New York.

Heat waves The IPCC projects that one lethal effect of global warming will be more frequent and more severe heat waves. Deadly stretches of hot days, where nighttime temperatures remain high, will become more common. One such event killed over 700 people in Chicago during the summer of By the year 2020, global warming could cause up to a 145% rise in mortality in New York City. Other major cities could suffer similar problems. A record heat wave scorched Europe in August 2003, claiming an estimated 35,000 lives. In France alone, 14,802 people died from the searing temperatures—more than 19 times the death toll from the SARS epidemic worldwide. In the worst heat spell in decades, temperatures in France soared to 104 degrees Fahrenheit (40 degrees Celsius) and remained unusually high for two weeks. August 2003 was the warmest August on record in the northern hemisphere, but according to the projections of the IPCC, even more extreme weather events lie ahead. By the end of the century, the world's average temperature is projected to increase by ° F ( ° C). As the mercury climbs, more frequent and more severe heat waves are in store.

Though heat waves rarely are given adequate attention, they claim more lives each year than floods, tornadoes, and hurricanes combined. Heat waves are a silent killer, mostly affecting the elderly, the very young, or the chronically ill.