Carbon Dioxide Emissions
The human activity most widely viewed as changing the planet is the burning of fossil fuels. In order to produce the energy that drives the world’s economy, countries rely on carbon-rich fossil fuels like coal, oil, and gas. By burning these materials, humans have added nearly 400 billion tons of carbon dioxide into the atmosphere between 1870 and 2013. Right now, atmospheric levels of carbon dioxide are higher than at any point in human history; the last time they were this high was 800,000 years ago. Carbon dioxide is a heat-trapping gas, and as a result of these atmospheric changes, average temperatures on the planet are rising and global weather patterns are changing. 2015 is expected to be the hottest year on record, following record high in 2014. Some of the carbon dioxide in the atmosphere is absorbed into oceans, increasing their acidity by 30 percent over the past 100 years. This change has far reaching affects on oceanic ecosystems and the food chains that support underwater plant and animal life.
Life depends heavily on the supply of fresh water that exists in rivers, lakes, and aquifers. According to Wired Science, it’s estimated that one fourth of Earth’s river basins run dry before ever reaching the ocean. This is the result of reduced rainfall caused by deforestation and the construction of man-made dams that divert water flow in inefficient ways. Less water flowing through river basins has also altered local weather patterns.
The Aral Sea, located on the Uzbekistan-Kazakhstan border, was once the fourth largest lake, but has now shrunk by 75 percent (see image above). The Aral Sea was once fed by two major rivers which now, due to human activity, run dry before they reach the lake. In the early 1960’s, the Soviet Union diverted water from the in-flowing rivers to irrigate rice and cotton crops in Central Asia. The reduced water flow caused salt concentrations to increase, making it inhabitable for the fish species that once lived there. The Aral Sea used to absorb heat during the summer and keep the temperature mild during the winters, but now that it’s drying up, the local climate is changing: in surrounding areas, summers are now longer and hotter and the winters are colder.
For centuries, humans have engaged in activities that produce black carbon particles. Black carbon particles are released into the atmosphere in the form of smoke that is produced by cooking with solid animal fuels, burning trees, and spewing diesel exhaust. When black carbon particles reach the atmosphere, they form a heat-absorbing layer that causes temperatures to rise. Raindrops tend to form around black carbon particles in the atmosphere, and when they fall to the ground, they absorb heat there too, thus magnifying their warming effect.
According to Science Daily, scientists estimate that 25 to 35 percent of black carbon in the global atmosphere was emitted by China and India from the burning of wood and cow dung in household cooking and coal to heat homes. Nations that rely heavily on diesel fuel for transportation also contribute large amounts.