MATTER: Climate Change
The ocean has been saving us. Its vast waters cover around 70 percent of the earth’s surface. It has absorbed more than 90 percent of the excess heat in the climate. But, in the process, the rate of ocean warming has more than doubled since 1993.
According to the IPCC (Intergovernmental Panel on Climate Change) special report on the Ocean and Cryosphere in a Changing Climate, approved on Sep. 24 by the 195 IPCC member governments, the planet is experiencing “unprecedented and enduring changes in the ocean and cryosphere.’’
The ocean is 96.5 percent water. In a water molecule, oxygen attracts the shared negative electrons more than hydrogen does. The electrons are therefore more often closer to the oxygen atom, which causes the oxygen atom to have a slight negative charge and the hydrogen a slight positive.
If another water molecule comes into the picture, that relationship is still sustained: the oxygen is slightly negative and the hydrogen slightly positive. This causes the oxygen of the first water molecule to form a weak bond, a hydrogen bond, with the hydrogen of the second; the oxygen of the second water molecule does the same. Because of these hydrogen bonds, it takes greater amounts of energy to move the water molecules. In this same line, it takes more energy to give the water molecules kinetic energy to break the bonds and evaporate the water molecules.
The ocean can absorb large amounts of heat without a significant change in temperature because, instead of heating the molecule, the heat is used to break hydrogen bonds. However, the ocean’s capacity to absorb heat is not limitless. From 1993 to 2017, the ocean has gained 0.36–0.40 watts per square meter for depths of 0–700 meters. The frequency of marine heat waves, which are prolonged periods of extremely warm temperatures, or more accurately when “seawater temperatures exceed a seasonally-varying threshold (usually the 90th percentile) for at least five consecutive days,” has doubled from the 1980s. This reshapes ocean ecosystems and provides the energy for severe storms, and also is projected to increase the frequency of El Niño, a periodic warming in sea surface temperatures, and La Niña, periods of below-average sea surface temperatures.
This decrease in sea ice has many prolonged repercussions. As the ice melts, the volume of the sea is set to increase, and by 2100, sea levels could rise by up to 1.1 meters if greenhouse gas emissions continue to rise. 1.1 meters may not sound high, but this will increase significantly the risk of flooding during storms. 680 million people in low-lying coastal zones will be dramatically impacted by these changes, but even in other parts of the world, the average sea level has risen around six-tenths of an inch per decade since 1880.
Ocean life is further threatened by acidification. As the concentration of CO2 in the atmosphere increases, the potential energy of the concentration difference between the concentration of atmospheric and ocean CO2 increases, and causes the CO2 to diffuse into the ocean. This excess CO2 reacts with water molecules to form carbonic acid, which then decomposes into a hydrogen ion and bicarbonate. The many hydrogen ions produced in that way cause the ocean to be acidic, decreasing the pH. As the ocean has absorbed between 20 to 30 percent of human-induced carbon dioxide emissions since the 1980s, surface ocean pH has dropped by 0.1 Ph units since the beginning of the industrial revolution. Even minor changes in ocean pH levels threaten fisheries and kill coral reefs.
This absorption of CO2 and the ocean’s absorption of heat has implications for ocean life, and through that, the state of the biosphere as a whole.