By Adam Stevens
Human beings are having a dramatic effect on our planet, even though the real power we wield over it is relatively small.
Look at this photo.
The simple act of painting some white lines on a patch of grass is enough to change the temperature variation across a few centimetres. So what happens when these changes are bigger? What impact does our small influence have on the planet?
I took the photo on a frosty morning, walking across an unused football pitch. You can see that the frost is thicker on the white marked part of the grass than on the unmarked grass. A simple thing, maybe, but underlying it is a fundamental part of science that could have drastic consequences for our planet.
The frost is thicker because the white grass has a higher albedo than the unpainted areas. A higher albedo means that it reflects more of the sun’s energy and absorbs less. This, in turn, means that the grass with paint on isn’t being warmed as much as the green patches around it. The effect is small–some small areas of frost linger on the grass around the lines, so the temperature different is maybe only a couple of degrees, but we can see it, and that’s important. Think about what would happen if we scaled this situation up from this few square metres to a continent sized area.
Ice and snow are very good examples of materials with a high albedo. In fact, they’re probably the best example, as snow covered ice has an albedo very close to one, meaning it reflects nearly almost all the sunlight that hits it.
Antarctica receives very little solar radiation, but what is does is mostly reflected back into space, since it is a continent almost completely made up of snow covered ice. Yet Antarctica is warming up. It may only be a fraction of a degree in a decade, but this is enough for us to observe massive sheets of sea ice collapsing around the coast, leaving behind nothing but drifting icebergs and (crucially) dark ocean water behind.
This tiny change in the temperature can, does and will continue to trigger a feedback effect that could drive climate change much faster than the small variations that caused it. A rise of a fraction of a degree starts removing ice from the continent. With less ice, Antarctica reflects less incoming radiation away from the planet, meaning it will warm up slightly more, triggering collapse of more ice, and so on. Antarctica contains more than half of the planet’s fresh water, so this process might well take thousands of years, but with the huge uncertainty in the real rates involved, it could take far less. With positive feedback happening, the process would speed up exponentially. We understand the mechanism, but cannot foresee the outcome. It’s possible that other processes that we understand less could reduce the overall feedback effect, or even work in the opposite direction. Our knowledge of the chaotic systems of our planet’s climate is lacking, but we do know that this small effect, this tenth of a degree of warming, could have big consequences.
At the other end of the globe there is another land of ice. The Greenland ice sheet may be melting quicker than previously thought, due to a rise of less than one degree in global temperatures. The melting may be less dramatic than its equivalent in the South, but it is still significant. In the permanently frozen landscapes around the Arctic basin, warming is causing the permafrost to melt, releasing methane gas previously trapped in frozen swamps.
Methane is one of the more effective greenhouse gas, second really only to water vapour. Both allow incoming solar radiation to pass unhindered, but trap outgoing thermal radiation. With more liquid water in the global hydrological cycle, as well as additional methane in the atmosphere, we would expect these gases to contribute more and more to global warming, adding to any possible effects of anthropogenic carbon dioxide.
This small amount of warming may not be happening everywhere. It would almost be strange if it was. If you blinkers on and only look at a local scale, it’s entirely possible some regions may be getting colder, almost making a mockery of the name global warming. Our climate is a complex system, with energy being traded across the planet in the wind and ocean currents. Yet these fluid motions also mean that small local changes can have wider consequences as their effects are carried far across the seas and continents.
The effects of global circulation quickly become apparent if you remove the blinkers. I’m sure many of you will remember coverage of El Niño, a particular weather system in the western Pacific. Caused by a slight difference in the normal pressure of weather systems at either side of the ocean, the El Niño Southern Oscillation changes the weather patterns of this area, bringing anomalously warm waters to the western coast of South America. We know now that it happens regularly, oscillating between extremes, possibly controlled by incredibly gradual warming of surface waters in the eastern Pacific.
El Niño was spoken of with dread in our lifetimes, and is still a worry, mostly due to the severity of the weather it created in the late 1990s, but the phenomenon has been probably been around for thousands of years. Only recently has it become more frequent and more extreme.
Small changes can have a big impact. El Niño requires temperature differences of less than a degree from the norm, but can cause a change in average temperature of several times that which started it. Melting ice, which requires less than a degree of change, reveals darker, more absorbent seawater that will cause more intense warming, setting up a feedback loop that we may never be able to break. Melting also releases water vapour and methane, both of which will contribute to an even more extensive feedback in the atmosphere.
It may be easy to skew the data, cherry pick, or ignore it entirely, but it’s far harder to hide the effects that we can see with our own eyes. We may only have a weak influence on our planet, but it’s more than enough. If our small influence can cause such big changes, then why couldn’t it work to reduce them too?