Dip your toe into the global ocean, and you won't notice any difference between 1970 and the present. Over the last 4 to 5 decades, average water temperatures in the ocean have warmed by about 0.04 degrees Celsius (0.07 degrees Fahrenheit.) Small as this temperature change is, when added up over the 4000-m (14,000-feet) depth of the ocean, it represents a monumental amount of heat. In fact 93 percent of the heat gain on Earth is linked to the warming of the ocean, with 3 percent due to heating of the land, 3 percent due to melting ice, and just 1 percent associated with the atmosphere.
We can attempt to put the enormous ocean heat gain into context by thinking about a 1500-watt electric hairdryer. The rate of increase of ocean heat from 1971 to 2010 has been estimated at about 200 trillion watts. That would be enough energy for each of the 7.3 billion people currently living on the planet to have run 18 hair dryers continuously for those 40 years. (Admittedly, many of those people would have had to start hair drying before they were born.) That is much more heat than most of us can possibly imagine needing. More soberingly, that energy is equivalent to exploding about 3 Hiroshima atomic bombs every second of those four decades. That is a jaw-dropping amount of energy.
What is the source of all this energy? It is not directly supplied by burning fossil fuel, or nuclear energy or any of the other energy sources that humans use. We simply don't consume that much energy. Global energy consumption from all sources in 2012 was about 17 trillion watts, less than 9 percent of the rate of ocean warming.
Instead the energy build up in the ocean comes from the Sun. If the Earth's climate were not warming, energy from the Sun that reached the Earth's surface, would all be reemitted to outer space. As carbon dioxide concentrations have increased in the atmosphere, this has resulted in more greenhouse warming and less reemission of heat to outer space. In short, increased carbon dioxide in the atmosphere is making the oceans warm.
A warming ocean has broad implications for climate, since the ocean serves as the heat storage for the planet. The atmosphere over the land will warm faster than that over the ocean, which will mean hotter summers and warmer winters too, shifting rain and snow patterns with drought across large swaths of the U.S. With these changes will come reductions in the productivity of agricultural land and the habitability of the cities where we live. Since seawater expands as it warms, a warming ocean also means rising sea levels. Because the ocean is so deep, and takes so long to warm, sea level will be rising for centuries to come as a result of the carbon we have already put into the atmosphere.
What can we do? If we want to slow the rate of warming in the atmosphere as well as the warming and rise of the oceans, we need to reduce carbon dioxide emissions. The challenge for us, as a society, is to develop carbon-neutral technologies that will meet our energy needs without committing us to yet more warming of our atmosphere and ocean.
This post is part of a month-long series produced by The Huffington Post in conjunction with a variety of events being held in September recognizing the threats posed by climate change. Those events include the UN's Climate Summit 2014 (to be held Sept. 23, 2014, at UN headquarters in New York) and Climate Week NYC (Sept. 22-28, 2014, throughout New York City). To see all the posts in the series, read here.