Wednesday, March 7, 2007

Global Warming and the impact of Extra Heat

What are the basics of Global Warming, specifically the impact of extra heat? What is extra heat? What is its impact on global warming? Feel free to make comments if you see things differently!

1. Natural Heat versus Extra Heat

The sun heats up Earth during the day. This solar energy constitutes natural heat, as opposed to extra heat that is added by human activity such as burning of fossil fuels. Simply said, extra heat comes on top of heat that comes naturally.

Sunlight reaches Earth with a strength of 174 PW or about 1.7 billion times the amount of power produced by a large electric power plant (which is some 100 million watts of energy). That is indeed a huge amount of power compared to the total human energy production, which was only 13.5 TW in 2001.

However, all this sunlight is needed to lift Earth's temperature all the way from the minus 454 degrees Fahrenheit (3 degrees Kelvin) of deep space to its current average temperature. In other words, it takes just a little bit of extra heat by comparison to increase the average temperature on Earth by a few degrees.

Also, we get a different impression if we look at the amount of energy deposited by the Sun per square meter. At the top of the atmosphere, the shortwave energy flux received from the Sun is about 1,368 watts per square meter. Because of its spherical shape, at any instant the Earth receives on average only half the incident solar flux, i.e. 684 W/m² . Due to the Earth's rotation, the average radiative flux received over a day-night cycle is half of this value, i.e. 342 W/m² .

Taking into account cloud coverage and the fact that the efficiency rate of capturing this energy with solar panels is rather low (say 10% to 15%), you can only expect an output of 19 to 56 W/m² or 0.45 - 1.35 (kW·h/m²)/day from solar panels.

How much extra heat is generated by human activity, compared to the heat resulting from sunlight? Firstly, the human body itself creates a lot of heat, but let not count that as "extra" heat for the time being. We're mainly looking at industrial activity, using electricity, cars and the like. A house will consume about 1kWe (kilowatt-electric) if measured as a continuous stream of electric power. If you keep the lights on in your office and your house, you may be using a few hundred watts of energy. A TV-set or a computer may use much more. If you drive home in your car, the engine generates a huge amount of heat. Vacuum cleaners, air-conditioners and refridgerators also use huge amounts, but they're not used continuously. On average, a typical person adds a few hundred watts of energy into the atmosphere, day and night, all year long. Currently, most of this demand is met by burning fossil fuel, which counts as extra heat that is added to the atmosphere.

As said, total human energy production was 13.5 TW in 2001. Since total Earth surface is 510,100,000 km2, the extra heat works out to be some 0.02 W/m², so it's rather insignificant when spread out over the entire globe.

2. The Greenhouse Effect and Global Warming

The atmosphere works like a greenhouse, shielding us from too much sunshine during the day, while also keeping heat trapped so that we do not freeze at night. In other words, the greenhouse effect shields us from both extremely high and low temperatures.

Greenhouse gases such as methane and carbon dioxide, as well as water vapor, trap such heat in Earth's atmosphere. The more greenhouse gases are released into the atmosphere, the stronger the greenhouse effect.

As said, activities such as burning of fossil fuels add extra greenhouse gases into the atmosphere, resulting in a stronger greenhouse effect. This will both result in both less sunshine getting through and less heat escaping the atmosphere, but the combined effect is a relatively higher overall temperature on Earth. Over the years, human activity, specifically burning fossil fuels, has substantially increased the amount of carbon dioxide in the atmosphere, resulting in a stronger greenhouse effect, causing global warming and climate change.

3. Positive Feedback

This global warming comes with positive feedback, i.e. the impact of global warming itself accelerates global warming and causes further increase of temperatures:

  • Decreased reflection of sunlight results in increased retention of heat. The overall albedo (reflection rate) of Earth will decrease. Sunlight is reflected more by white surface (such as snow), compared to darker surface (such as rock and soil). As the albedo decreases (which is the case when snow melts), less light is reflected and more heat is absorbed by the soil. Albedos can be as high as 90% for snow and as low as 4% for charcoal. Most land areas have an albedo range of 10 to 40%. The average albedo of the Earth is about 30%. As the permafrost, the ice and snow in the polar regions melts, as the iceplates in the Arctic regions break loose and icebergs float away, as less snow falls in the mountains and as glaciers melt, all these areas change color from white to dark. All this causes a further rise in temperature, as the darker soil and sea absorb more sunlight and thus heat up, where previously the sunlight was reflected back into space by the white ice and snow.

  • As the permafrost melts and disappears, thawing boreal forests, swamps and tundras will emerge that - as bogs heat up and peat thaws - will release huge amounts of methane gas, a twenty times more powerful greenhouse gas than carbon dioxide.

  • Global warming will come with more extreme weather conditions. Floods typically cause a huge loss of top-soil. Rotting and decomposing trees release methane, as do the termites that feed on them. Land clearing, over-grazing, droughts and fires further put entire regions at risk of desertification. The Amazon rainforest, the African tropics, the tropical rainforests in Indonesia, they all risk turning into savannah and deserts, releasing the carbon stored in trees as carbon dioxide into the air and releasing huge amounts of methane in the process, while also decreasing the capacity of soil to absorb carbon dioxide.

  • As snow melts, more humidity gets into the air. This vapor constitutes another important greenhouse gas. As Earth heats up, the amount of water vapor in the atmosphere will increase, as more water evaporates at the surface, both on land and at sea. This causes a further increase in the greenhouse effect and thus a further increase in atmospheric temperature.

  • The human factor also constitutes an important form of positive feedback that's often overlooked by climatologists. More extreme weather conditions can be expected, i.e. droughts followed by floods and storms, followed again by droughts, etc. This will result in larger run-off of fertile top-soil. Farmers may try to adapt to climate change, but it will take years before they will have found the best types of plants for the new conditions. The result will be higher food prices and demand for new agricultural areas. Rising sea levels, droughts, storms and floods will make people leave low-lying coastal areas and move to higher grounds, where they will start clearing trees for agriculture, industry, roads and housing. The overall result will be increased loss of forests. Thus, the human factor is expected to constitute another positive feedback, as discussed further in the Ten Dangers of Global Warming.

In other words, Global warming comes with 'positive feedback', which means that we're not only stuck with global warming for some time to come, but we can only expect things to get worse, even if we did decide to stop adding any further greenhouse gases and extra heat (i.e. on top of the heat and gases that come naturally).

4. Impact of Extra Heat

All extra heat that we release will add to global warming. As said, it seems rather insignificant compared to natural heat from the sun, from geysers and other natural geo-thermal sources. It also seems insignificant compared to the natural heat that remains trapped in the atmosphere due to the extra amounts of greenhouse gasses we produce. Neverthless, as more heat remains trapped in the atmosphere due to an accelerating greenhouse effect (since global warming comes with all kinds of positive feedback), its significance is increasing. Extra heat may become increasingly important in assessments, e.g. when subsidies are allocated to the type of energy that produce the least extra heat.

5. Nature versus Human Activity

In many respects, human activity is to blame for global warming. Burning of oil and coal are obvious human activities that result in global warming. While nuclear power plants may look better in terms of greenhouse gases compared to burning of fossil fuels, nuclear plants will also directly add extra heat into the atmosphere. In the light of the accelerated greenhouse effect, such extra heat remains - even more than before - trapped in the atmosphere, adding further acceleration to the already accelerating global warming. As said, extra heat may seem insignificant compared to natural heat, but it may just tip the balance when deciding how to allocate subsidies to combat global warming. Similarly, where geothermal schemes extract heat from the depths of Earth, this may also constitute extra heat that wouldn't be added naturally.

Agriculture can also add substantial amounts of extra heat: animals release methane gas, clearing land for agriculture by burning forests releases carbon dioxide, inefficient farming practices result in release of nitrous oxide, etc. In Australia, greenhouse gas emissions from agriculture constituted 16% of total emissions in 2004 (source), while agriculture was largest source of nitrous oxide and methane emissions (source).

But that doesn't mean that all human activity was bad and that all farms needed to be transformed into forest overnight. Bad forestry practies also add extra greenhouse gases, due to composting and formation of swamps resulting in methane, and due to natural burning and firestorms. Many forests would burn naturally and this can be minimised with good forestry management. Similarly, termites release methane gasses, so it makes sense to avoid this.

Banning all human activity and letting nature go rampant is not the answer. The big challenge is to find ways in which we can live, work, travel and do things we want to do while minimising our contributions to further global warming. Capturing the heat of the sun and geysers, and capturing the turbulance of wind, waves and rivers is not only a way to use energy that is already present naturally, it can also flatten wild weather patterns that could do a lot of damage.

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