“Albedo”—rhymes with speedo—is one of those words that I can’t help wishing more people used and understood, for two reasons. One is that it is just very euphonious; pleasant to say and hear, nicely weighted with its stressed middle syllable, endowed with pleasantly open vowels, a tad romantic in that latinate terminal “-do”—tuxedo, desperado and, indeed, libido have some of the same charm.
People are used to talking about climate change in terms of how much the world’s average temperature has risen. (Unsplash)
When Johann Heinrich Lambert, a polymath best known these days for creating a map projection that accurately reproduces the relative areas of countries and continents, coined the word in the 18th century, these considerations were probably not uppermost in his mind. He just wanted a term to describe the amount of incoming light that a body or surface reflects. And that leads to the second reason for wanting albedo to be more widely used. It makes writing about climate change a lot easier.
This week we ran a coverpackage on Earth’s declining albedo and how it is hastening climate change. As this lovely graphic explains, the albedo fluctuates in a regular way over the seasons, peaking with the spread of ice and snow in the northern winter. But it also changes from year to year, and a quarter century of carefully calibrated measurements shows that those changes have a distinct downward trend.
If the share of the light being reflected is dropping, the amount being absorbed has to be growing. The amount of heat Earth is giving off in the infrared is growing too—but not enough to offset all the growth in absorption. So Earth has an “energy imbalance” which is getting larger. And this would all be easier to explain if the word albedo were in widespread use.
Nomenclature, though, is as nothing compared with units of measurement. People are used to talking about climate change in terms of how much the world’s average temperature has risen. This seems straightforward, but constructing an average global temperature from lots of local measurements is difficult; the number depends on arcane details of methodology—which is why it makes sense to have a number of different teams of scientists estimating it independently.
Earth’s energy imbalance is, by most lights, a more meaningful indicator of the true scope of climate change. But for all its drawbacks, average global temperature is at least measured in sensible units: degrees Celsius (or Fahrenheit for Americans). The energy imbalance is measured in watts per square metre—a unit of remarkable obscurity.
Multiplied by the planet’s surface area, it becomes gigawatts or terawatts, which at least some people can picture: a gigawatt is roughly the output of a big nuclear power station. A terawatt (a thousand gigawatts) represents a substantial fraction of all the energy used by humans—it is something like a sixth of the rate at which useful energy is extracted from fossil fuels.
The problem is that translating planetary flows of energy into the units utilised for energy use at the scale of an industrial civilisation makes the numbers look like misprints. An energy imbalance of 1.2 watts per square metre, expressed in terms of the actual energy flow for the whole Earth, clocks in at over 600TW—one hundred times the energy from fossil fuels. The total “forcing” from the greenhouse gases in the atmosphere because of human actions is currently around 1,800TW.
I go into all this partly for fun (and I apologise if our ideas of fun differ) and partly to introduce a fundamental fact about climate change: its leverage. It can seem strange that such mighty things as hurricanes, droughts and ocean currents respond to the number of cars or coal mines. But they do, because the amount of useful energy gained by burning fossil fuels is utterly dwarfed by the warming caused by the carbon dioxide released in the process.
Consider natural gas, the cleanest fossil fuel, being burned in an efficient modern power plant. For every kilowatt-hour of electricity generated the plant emits just under 300 grams of carbon dioxide. Within its first two months in the atmosphere, that 300g of carbon dioxide will contribute a kilowatt-hour to global warming, balancing the energy the power plant produces. And it will then do the same every two months for centuries to come. The energy that carbon dioxide traps over its lifetime in the atmosphere will be a thousand times the energy provided as electricity by burning the gas in the first place.
The leverage is incredible. It allows the energy requirements of a few billion people to alter the energy balance of the planet on a scale similar to major shifts in the output of the Sun itself. Or, for that matter, in Earth’s albedo. Thinking humans can change planets is not hubris. It’s physics.
Home/Environment/The Climate Issue Newsletter: The Dangers Of Global Dimming
E-Paper
