【明報專訊】Every one of us has a part to play in environmental protection. This is one of the messages of Earth Day (世界地球日), which has been celebrated annually on 22 April for 45 years.

◆1. The first Earth Day

A day to honour the Earth and the concept of peace was first proposed by John McConnell, an American peace activist, at a UNESCO (聯合國教科文組織) conference in San Francisco in 1969. A separate Earth Day was founded by United States senator (參議員) Gaylord Nelson on 22 April 1970.

Over the decades Earth Day has been an influential grassroots movement and has helped raise public awareness of the need to protect the environment and promote various environmental protection efforts (like the recycling movements in the 1990s).

◆2. What are the biggest threats our Earth is facing?

The celebration of Earth Day reminds us of the threats the Earth is facing. Here are some examples:

(a) Climate change

Climate change is a long-term shift in weather conditions identified by changes in temperature, precipitation (降雨), winds, etc. There are many causes of climate change. They include biotic (生物的) processes, variations in solar radiation the Earth receives, plate tectonics (板塊運動) and volcanic eruptions. But scientists are generally agreed that the "greenhouse effect" caused by human activities is the culprit in the current global warming trend.

(b) Air pollution

Politicians like to claim population growth will do us more good than harm. But a growing world population is in fact one of the most obvious threats to the environment. A bigger population means more consumers, who use more of the Earth's resources. This causes more and more pollution. Atmospheric particulates (懸浮粒子) and heavy metals in water and soil all cause health problems.

(c) Loss of biodiversity

Biodiversity refers to the variety of plants and animals in a particular place. On the Earth, the loss of biodiversity is mainly caused by pollution and humans' hunting of certain kinds of animals. The extinction or diminishing population of a specific species could have a hazardous effect on the Earth. For example, the population of bees has a direct effect on both the environment and food production because of their role in pollination (傳播花粉).

(d) Deforestation

By felling trees we have reduced the amount of oxygen in the air and displaced wildlife. But more importantly, deforestation has rendered the Earth less protected against global warming. It has done so because it causes carbon dioxide to stay longer in the atmosphere, producing a layer in it that traps radiation from the sun.

(e) Ozone depletion

Chemicals and chlorofluorocarbons (氯氟烴) created by industry and agriculture have a negative impact on the ozone layer (臭氧層). The decrease in the amount of ozone in the ozone layer around the Earth's Polar Regions has caused a problem known as the "ozone hole". Reductions in stratospheric ozone levels lead to higher levels of Ultraviolet B (紫外光B, UVB) reaching the Earth's surface, making humans more susceptible to skin cancer.

(f) Rising sea levels

Rising sea levels are another major threat posed by global warming. As polar ice continues to melt, not only are low-lying countries (like the Netherlands and the Maldives) under threat, but cosmopolitan cities like London and New York could be in danger too.