The Unseen Atomic Bombs

The Unseen Atomic Bombs

For those of us trying to help Americans understand climate science, it doesn’t help that carbon dioxide, the key product of fossil fuel combustion that is driving climate change, is invisible. For many people it is hard to imagine how an invisible gas that makes up 0.04% of the atmosphere can be responsible for changing the temperature of the planet. Despite the fact that this has been understood since the 19th century, many people just cannot accept this as true (including Secretary of Energy Rick Perry).

What if hundreds of thousands of atomic bombs had been detonated every day in the ocean for over 50 years? I think people who can’t accept the role of carbon dioxide in climate change would find it easier to accept that an impact of these bomb explosions could change the temperature of the earth.

The thing is, from the perspective of energy, adding invisible carbon dioxide and detonating the bombs have the same effect (I first saw this comparison made by James Hansen).

As we all know from our daily lives, increasing the temperature of something requires energy. The carbon dioxide (and water vapor) in our atmosphere absorb energy that would otherwise escape into outer space, and we’ve known for a long time that this warms the planet. Physicist John Tyndall wrote in June, 1859, “the atmosphere admits the entrance of the solar heat, but checks its exit; and the result is a tendency to accumulate heat at the surface of the planet.”

Since the time of Tyndall, the burning of fossil fuels has increased the concentration of carbon dioxide in our atmosphere by 40%, further reducing the loss of energy to outer space. Tyndall could have told us this would happen, and we’ve now measured the change using satellites.

But still, if carbon dioxide is only 0.04% of the atmosphere, the energy that is staying on earth instead of heading to outer space can’t amount to much, right? Since we know the chemical properties of carbon dioxide, we can calculate the amount of energy that no longer escapes to space. Scientists measure energy in joules, and the flow of energy over time in watts. One watt is defined as one joule per second (so a 100-watt lightbulb uses 100 joules of energy per second).

The reduced flow of energy to outer space due to the additional carbon dioxide (and other greenhouse gases) can be calculated to be approximately 0.5 watts per square meter of the earth’s surface. This doesn’t seem like a lot (think about how dim a 0.5-watt light bulb would be!). But when you realize that this is happening over the entire surface of the earth (more than 500 billion square meters), the altered flow of energy is about 250 billion watts. These gases may be invisible, but they are powerful.

Most of this extra energy has been absorbed by the ocean, which consequently has warmed by an average of about 1°F over the last 55 years. As the ocean warms, sea level rises, ice sheets melt, winds and currents change and weather events get more extreme. These changes create adverse impacts on ecosystems and human civilization. The 1°F temperature increase represents a lot of energy – about 1023 joules (that is a one with 23 zeros). This is 10 billion times the amount of energy (1013 joules) released by the atomic bomb that destroyed Hiroshima.

So now we can do the math (see below) to compare, from an energy perspective, the invisible gases to the bomb explosions. The energy that has accumulated in the ocean over the last 55 years is equivalent to the energy released by exploding about 400,000 Hiroshima-sized bombs every day over that same time period.

The Math:

(400,000 bombs/day) x (365 days/year) x (55 years) = 8 x 109 bombs in 55 years

(8 x 109 bombs) x (1013 joules/bomb) = 8 x 1022 joules or approximately 1023 joules

Clearly, people who “just can’t believe” greenhouse gases can impact the temperature of the earth are underestimating their power. But as Neil deGrasse Tyson has noted, “science is true whether you believe it or not.”