The Water Cycle

Many experts believe that water depletion will be one of the most pressing issues of the 21st century. Currently, one third of humans have inadequate access to clean, fresh water. By 2025, the number is expected to reach one half to two thirds of the human population, thanks to a combination of many factors, including water pollution, climate change, and water depletion from unsustainable water uses.

Inadequate water resources have led to violent conflict throughout human history, but never on the scale that is likely to affect the 21st century. In addition to human suffering and armed conflicts, unsustainable water use also affects the environment as a whole. For example, irrigation of crops can lead to salinization of soil, ultimately leading to desertification and loss of habitat and biodiversity. Another concern is rising ocean levels. Recent studies have linked groundwater depletion around the world to rising sea levels. Rising sea levels already threaten many island nations and low-lying coastal regions.

Ocean Acidification

Ocean acidification is a lesser known side effect of excessive CO2 production. About 1/4 of the CO2 produced by human activities every year is dissolved in the oceans, where it reacts to form various compounds, including carbonic acid, that increase the acidity of seawater. Over the last 250 years, surface acidity of the ocean has increased by an estimated 30%. The acidity is expected to increase by 150% by 2100.

The effects of this change are still poorly understood. However, what is known is that increased acidity decreases the amount of carbonate in seawater, an important component of shells for many shellfish and plankton, and skeletons for coral. The effect of more acidic seawater is similar to that of the disease osteoporosis on human bones – the shells and skeletons gradually become softer and weaker. Eventually, the shells and skeletons dissolve completely. Since shellfish and plankton provide food for many other creatures and coral reefs offer one of the richest and most biodiverse ocean habitats, this could result in a disastrous domino effect for ocean ecosystems, leading to the collapse of many fisheries and eventual extinction of thousands of species.

Chemical Pollution

Pollution of air, water, and soil by long-lasting chemical compounds is another tipping point that is hard to quantify, in part because many of the chemicals in question simply have not been around long enough for their long-term effects to be clear. These include many compounds suspected of being endocrine disruptors, chemicals that interfere with the natural balance of hormones in the body. Some of these endocrine disrupting chemicals are blamed for a sudden rise in hermaphroditism among aquatic creatures such as fish and frogs. Others are believed to contribute to the rise in breast cancer, prostate cancer, and other hormone-related cancers in humans.

Other pollutants, such as some heavy metals, are already known to be both harmful and persistent.