Decrease global warming by raising crops with a high albedo

albedo-dartmouthBy growing crops the reflect more of the sun’s ray back off the planet, over the next hundred years, could avert the carbon footprint of 195 billion tons of CO2 emitted into the atmosphere. Farmers could choose to grow crops with high carbon credits.
Varieties of food crops can be grown in  much of Europe and North America that could help lower the albedo or  cooled by up to 1C during the summer growing season, say researchers from the University of Bristol, UK. This is equivalent to an annual global cooling of over 0.1C, almost 20% of the total global temperature increase since the Industrial Revolution.

What traits of a plant lowers its albedo

The growing of crops already produces a cooling of the climate because they reflect more sunlight back into space, compared with natural vegetation. Plants differ in their albedo because of differences in the properties of the leaf’s surface and how the leaves are arranged (called ‘canopy morphology’). By carefully selecting a variety or varieties of the a food crop for its solar reflectivity (‘albedo’) the cooling effect could be extensive globally. Dr Andy Ridgwell and colleagues at the University of Bristol research suggests that the most albedo crops would exert a control on the climate, in the same way that we currently cultivate specific varieties to maximize and fine-tune food production.

Dr Ridgwell said: “With this approach in a global climate model, our best estimate suggests that summer-time temperatures could be reduced by more than 1C throughout much of central North America and mid-latitude Eurasia.”
Growing more reflective crops are a realistic way of helping reduce the severity of heat waves and droughts in these regions. Results could be achieved very quickly and at very little cost.

Ridgwell has calculated that if such a mechanism were in place farmers might expect to earn in the region of 23 euros per hectare (or 29.99 USD US per 2.47 acres) per year for the warming averted. Biofuels currently earn 45 euros per hectare (58.68 USD per 2.47 acres )per year, but take up valuable agricultural land needed for growing crops.

To avoid excessive global warming, we need massive emissions reductions and soon says Chris Huntingford of the UK Center for Ecology and Hydrology this particular proposal may have fewer unwanted consequences than other proposals to “geo-engineer” the climate, such as fertilizing the entire oceans with iron filings.”

More ways albedo effects the global climate

In the tropics

Although the albedo-temperature effect is most famous in colder regions of Earth, because more snow falls there, it is actually much stronger in tropical regions because in the tropics there is consistently more sunlight. When ranchers cut down dark, tropical rainforest trees to replace them with even darker soil in order to grow crops, the average temperature of the area increases up to 3 °C (5.4 °F) year-round, due in part to changes in evaporation.

Albedo ‘s many effect180px-albedo-e_hgsvg

People who wear dark clothes in the summertime put themselves at a greater risk of heatstroke than those who wear lighter color clothe

Trees

Because trees tend to have a low albedo, removing forests would tend to increase albedo and thereby could produce localized climate cooling. Cloud feedbacks further complicate the issue. In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 while coniferous trees have a value of about 0.09 to 0.15. The difference between deciduous and coniferous is because coniferous trees are darker in general and have cone-shaped crowns. The shape of these crowns trap radiant energy more effectively than deciduous trees.

Studies by the Hadley Center have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and mid-latitude areas tended to cool; new forests in high latitudes like Siberia were neutral or perhaps warming

Snow

Snow albedos can be as high as 90%; this, however, is for the ideal example: fresh deep snow over a featureless landscape. Over Antarctica they average a little more than 80%. If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt

Water

Water reflects light very differently from typical terrestrial materials. The reflectivity of smooth water surface at 20 C has a refractive index=1.333. Even wavy water is always smooth so the light is reflected in a not diffusely. The glint of light off water is a commonplace effect of this. Although the reflectivity of water is very low at low and medium angles of incident light, it increases tremendously at high angles of incident light such as occur on the illuminated side of the Earth during early morning, late afternoon and near the poles. White caps on waves look white and have high albedo, because the water is foamed up. However fresh ‘black’ ice exhibits Fresnel reflection.

Cloud

Clouds are another source of albedo that play into the global warming equation. Different types of clouds have different albedo values, theoretically ranging from a minimum of near 0% to a maximum in the high 70s. “On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth.

mean_annual_albedo1

The annual mean albedo effect around the world (chart at the right). Notice the gray to white areas at the top and bottom they equal energy radiation of near 100% back towards the atmosphere.

Resources

Cooling The Planet With Crops – Staff Seed Daily, Bristol, UK (SPX) January 22, 2009. Cooling_The_Planet_With_Crops

The Encyclopedia of the Earth Albedo -Dagmar Budikova eoearth.org/article/Albedo

University of Minnesota AlBedo

Excerpts Courtesy of Wikipedia Albedo Effects

Image 1. Courtesy of Dept. Engineering Dartmouth engineering.dartmouth/albedo.jpg

Image 2 Courtesy of Wikipedia Albedo Effects

Image 3. Courtesy of  EOEarth.org eoearth.orMeanAnnualalbedo

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