Sunday, April 17, 2011
Things that Go Bump in the Twilight
Above is the NASA Earth Energy Budget cartoon. While it is simplified, it still shows that there is a lot going on. It only takes a small change in any of the percentages shown to make a pretty big difference in climate. If you combine the incoming reflected arrows, 30% of the Sun's energy is reflected to space. Clouds are the largest reflected component. Cloud cover can increase by a couple of percent and wipe out all the greenhouse gas increased forcing. With rising temperature there is more water vapor so there is a good likelihood there will be more clouds. That is not my theory. Plenty of other people are arguing over that one. Surface reflection is only 4% and atmospheric reflection is only 6% with most of that happening above the tropopause.
For the surface reflection to impact climate there has to be a larger percentage change in surface albedo to have the same impact as cloud cover change. That is not to say that surface albedo is not important, it just has to change more to have a similar impact as the constant changes in cloud cover. Two of the biggest surface albedo changes are snow cover, sea ice and land use.
Since we are talking about reflection, it is easy to see how bright white snow is reflective. That bright white gets less bright with dirty dust and ash fall out on the snow. Most of that fall out we have some control over. In the US and other top economies, air pollution is a big deal so there has been great progress cleaning the air by removing ash from energy use. Developing nations are finding out that too much air pollution is really bad, so they will be forced to reduce air pollution either by their own problems or neighboring nation getting hacked off. So in the normal course of growing, ash or black carbon will be reduced. A little extra bitching can speed that process up, so I am not particularly concerned with the black carbon part of the puzzle.
Land use is a lot more complicated. Farming and housing expansion are are the main things changing land use. The great dust bowl of the 30's forced the US and Canada to rethink farming practices, which was watched closely by other nations. So dust from agriculture is becoming less of a problem. Part of the solution though, irrigation, adds a new dimension to the puzzle. Areas which once had lower humidity are now irrigated increasing the local temperatures, mainly at night. Wetlands have been drained to increase farmland and provide more land for housing expansion. Forests have been cut down as well. While it is harder to visualize, forests and natural wetlands have more than just albedo impact. Many plants, especially trees, can control their temperature somewhat. It is cooler under trees not only because of the shade, but also because photosynthesis is an endothermic chemical process. That means leaves absorb heat energy and basically exhale cooler temperatures.
Humans have been whacking down trees forever. They provide shelter and fuel. They also block sunlight needed for farming. More trees are a good thing, but with the drive for biofuels and food, forest areas are still under huge pressure. This is a dicey issue. You can't ask people to starve for the good of mankind. You can bite the bullet and choose less "Clean" and "Safe" energy sources to reduce agricultural demand. You can also support a more symbiotic relationship between humans and environment. This forces opinionated buttheads to realize that the enemy of my enemy is my friend. The PETA and Enviro whack jobs have to understand that the Hunting Whack jobs share a common goal, more natural wood lands and wet lands. The hunting whack jobs have done more to preserve natural game habitats than the PETA and Enviro whack jobs have in the past few decades. Will the whack jobs come to their senses? I doubt it, some people are pretty dense. PETA guys for example are big into "organic" things like bananas and neat tropical fruits. Where are the bananas and neat tropical fruit grown? In areas that were once rain forests. They would have a bigger impact trying to ban coffee, bananas, palm oil and ethanol. So PETA promoting "EAT MOR Chickin", the other white meat, or Hassenpfeffer, would be supporting more food protein per unit land than banning meat. Most humans are omnivores, get over it!
So surface albedo is pretty much either going to take care of itself or not. Cloud cover changes are going to be debated. CO2 is going to continue to rise until people embrace energy reality. Nukes are scary, dangerous and expensive, but they are very clean compared to the other choices which seem to always be the energy of the future. Until then, people are still going to screw up pushing bright ideas that have unintended consequences. That is just the way it is.
So that brings me back to the tropopause and why people are not the sharpest tacks in the box. People are opinionated and suffer from politically focused tunnel vision. That causes us to miss the obvious. This planet has been around a lot longer than us, so it probably has a few tricks left up its sleeve. Man has not even come close to exploring the atmosphere's response to our impact.
So why did I title this post Things that go Bump in the Twilight? Because when you model the Troposphere in day or night mode you can miss the subtle activities of the in between. Day and night may be the big players, but it only takes a few percent to make big changes. The radiation balance of the tropopause changes big in the twilight. There is no up or down as far as radiation is concerned, only hard or easy. It is easy to see the change in incoming solar. The angle is different, scattering increases, there is less absorbed and reflection. Why would we assume it is any different for longwave? Longwave interacts with the Greenhouse gases more than the inert gases. That heats them. Water vapor has a much broader spectrum than the other greenhouse gases, so that heat in the form of infrared radiation flows to cooler areas. In the tropopause, every thing in every direction is cooler except for down. So as heat is transferred to the tropopause by convection, greenhouse warming or mixing rising air, it has a lot of paths open to it to escape to space. The remarkable stable temperature of the Tropopause trend shows that those paths are used, we just don't know how well.
Perhaps, thinking in a twilight perspective is the easiest way to explain the wondrous protection the Tropopause gives us as a thermostat to control temperatures. Looking at the Tropopause, very small changes would give us that few percent that has the big impact on climate.
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- ▼ April (33)