THE scientific evidence continues to mount. The climate is changing, the effects are already being felt and human activities are a principal cause.

“Without effective action, climate change is going to be larger and more difficult to deal with than we thought,” said Dr. Chris Field, who was a coordinating lead author of the report issued by the Nobel-winning Intergovernmental Panel on Climate Change (IPCC).

Climate change results from the Earth’s atmosphere allowing light to penetrate and reach the planet but preventing heat generated after light hits the ground from radiating back into space. This condition is attributed to the 30-percent rise in carbon dioxide since pre-industrial times from the use of fossil fuels burnt by motor vehicles, power stations and other human activities.

Carbon dioxide, however, is just one of the so-called greenhouse gases. Others are almost exclusively produced by human activity such as chlorofluorocarbons (CFCs), from air conditioners and refrigerators, and nitrogen compounds. Ground-level ozone, produced by burning fossil fuels, is also considered a greenhouse gas. (Don’t confuse ground-level ozone with the ozone layer that is 10 and 60 kilometers above the Earth’s surface.)

According to science, climate is weather averaged over the long term: decades, centuries and millennia. It is a tremendously complex system that comprises not only the atmosphere, but also the oceans, ice, the land and its features, as well as rivers, lakes and sub-surface water. The sun’s output, the Earth’s rotation, and the chemical composition of the atmosphere and ocean all affect this system. Changes in any of these internal or external factors are responsible for the climate’s variability.

While the climate has undergone some wild shifts over the course of geological history, it has been relatively stable during the period in which modern human society has evolved. But with the warming that is projected from the gases that humans are adding to the atmosphere, this stability may come to a man-made end.

Scientists say that as the Earth’s thermostat continues to climb, human health problems will only become more frequent. Researchers have found that there is a close link between local climate and the occurrence or severity of some diseases and other threats to human health.

In the last quarter of the 20th century, the average atmospheric temperature rose by about 1 degree Fahrenheit. “By 2000, that increase was responsible for the annual loss of about 160,000 lives and the loss of 5.5 million years of healthy life,” deplores the Geneva-based World Health Organization (WHO).

The toll is expected to double to about 300,000 lives and 11 million years of healthy life by 2020.

“The warming of the planet will be gradual, but the effects of extreme weather events will be abrupt and acutely felt,” said WHO Director General Margaret Chan. “Both trends can affect some of the most fundamental determinants of health: air, water, food, shelter and freedom from disease.”

Here are some examples of what’s already happening due to global warming:

During the past two decades, the prevalence of asthma in the United States has quadrupled, in part because of climate-related factors. For Caribbean islanders, respiratory irritants come in dust clouds that emanate from Africa’s expanding deserts and are then swept across the Atlantic by trade winds, which have accelerated due to warmer ocean temperatures.

Starting in August 2003, heat waves caused more than 14,800 deaths in France. Belgium, the Czech Republic, Germany, Italy, Portugal, Spain, Switzerland, the Netherlands and the United Kingdom all reported excess mortality during the same period, with total deaths in the range of 35,000. In France deaths were massively reported for people aged 75 and over (60 percent).

Six young men and boys were killed by fatal parasites in 2007 at Lake Havasu, Arizona, after they swam in water infested with a heat-loving amoeba. In 2008 scientists found that poison ivy vines have grown 10 times denser near Savannah, Georgia, over the last 20 years. “Increased carbon dioxide in the atmosphere causes poison ivy to grow larger and produce stronger irritants,” they reported.

Mosquitoes and the diseases they carry—including malaria, dengue fever, Ross River virus, and West Nile virus—are especially sensitive to temperature changes and land elevation. Mosquitoes that carry malaria were found at never-before-seen elevations on Mount Kenya in 2006. Malaria has also been detected in new higher-elevation areas in Indonesia. Mosquitoes that can carry dengue fever viruses were previously limited to elevations of 3,300 feet but recently appeared at 7,200 feet in the Andes Mountains of Colombia.

Smog-related deaths from climate change are projected to increase by about 4.5 percent from the 1990s to the 2050s, according to studies at Columbia and Johns Hopkins universities. A scientist at Yale University, Michelle Bell, looked at the 50 largest cities in eastern United States and found that the health-alert days would go up by 68 percent over the next decades.

Over the period of 1995-2004, a total of 2.500 million people were affected by disasters, with losses of 890,000 dead and costs of $570 billion. Most disasters (75 percent) are related to weather extremes that climate change is expected to exacerbate.

“A massive increase in the frequency of occurrence of natural disasters such as floods, earthquakes, tsunamis, forest fires have been observed in last decades and have a direct impact in human health,” the WHO said in a statement.

Approximately 600,000 deaths occurred worldwide as a result of weather-related natural disasters in the 1990s; some 95 percent of these were in poor countries. According to the Oxfarm report (November 2007), the average number of natural disasters per year during the early 1980s was about 120. Now, the number has increased to nearly 500.

“Without urgent action through changes in human lifestyle, the effects of this phenomenon on the global climate system could be abrupt or even irreversible, sparing no country and causing more frequent and more intense heat waves, rain storms, tropical cyclones and surges in sea level,”warned Dr. Shigeru Omi, the Asian regional WHO director.

WHO Director General Dr. Chan has few words to say: “Climate change endangers human health.”