Perhaps my idea of planting trees to absorb carbon wasn't such a good 
one after all, if they are going to increase heat retention?

Chris

-------- Original Message --------
Subject: 	Albedo
Date: 	Mon, 04 Jun 2007 11:28:41 +0100
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BrianDavey has posted "Albedo" in "Energy and Climate Working Group" at the FEASTA forum. If you wish to post a reply to the whole Energy and Climate Working Group , please use the following link to do so:

http://www.feasta.org/forum/posting.php?mode=reply&t=144

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The general assumption is that human induced climate change - anthropogenic induced - climate change started in 1750 with the industrial revolution and the carbon emissions that started at that time.

Not so, according to researchers at the Met Office who looked at another reason that global temperatures change in addition to the greenhouse gas caused changes - changes in the earth's albedo. The earth's albedo is the amount of incoming solar energy reflected back into space from the earth's surface. The greater the reflection the less the warming down on earth - for example in the Arctic where it is snow and ice covered more than 90% of the sun's energy can go straight back into space. (Albedo of more than 90%).

The significance of this is that land use changes also change albedo. In general agricultural land has a greater albedo than forested land.

"Forty-nine million ha of the global land surface is currently classified as either crops, pasture or grazing, meaning that at least 34% of the global land surface is subject to direct alteration by human activities. The albedo of agricultural land can be very different to that of a natural landscape, especially if the latter was forest, with the albedo of open land being generally higher than forested land. Changes in surface albedo change induce a forcing of climate by perturbing the shortwave radiation budget. The effect is particularly accentuated when snow is present, and surface albedo change may therefore provide the dominant influence of mid- and high-latitude land cover change on climate."

The clearing of forests for agricultural land (which happened extensively in Europe prior to 1750 ) therefore has two effects - on the one hand the carbon in the forests and the disturbed soils eventually enter the atmosphere increasing temperatures - on the other hand the greater albedo of agricultural land has a cooling effect. This effect is felt particularly powerfully at a local and regional level - rather than locally

Meterological Office researchers Richard A. Betts, Kees Klein Goldewijk, Navin Ramankutty therefore speculate that in pre industrial times the increased CO2 from land use changes would have been eventually reabsorbed by sinks but the albedo changes would have been permanent. The long run net effect would therefore have been a cooling. 

"Land use change could therefore have contributed to the Northern
Hemisphere cold period of the 17th Century (the “Little Ice Age”)."

http://www.metoffice.gov.uk/research/hadleycentre/pubs/HCTN/HCTN_70.pdf

These are issues that have relevance when we try to consider policy responses to climate change. It is not just that planting tree plantations as carbon offsets promotes a new form of plantation economy and is of dubious benefit because of the time they take to mature and therefore take CO2 out of the atmosphere, nor that the trees will eventually die and put their CO2 back in the atmosphere....it is also that afforestation may have a lower albedo and therefore absorb much more of the sun's energy at the surface. This is particularly if it occurs where there would have been snow.  

These kind of policy issues were summarised like this by leading researchers  in a paper that is already several years old but still being cited as an important reference into these issues:

“Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in the terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land-surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated !
 with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate should not, however, be used as an excuse to avoid actions that would minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental  change and variability. ”

Further:

“There has been widespread acceptance that at some level sequestering carbon in the terrestrial biosphere has the same effect on atmospheric CO2 as does reducing emissions of CO2 (IPCC, 2000). We point out that whereas the immediate effect on atmospheric CO2 may be the same, the effect on the Earth’s climate is not the same. Climate is the interaction of all of the components of the Earth system and it includes the solar and infrared radiation and sensible and latent heat fluxes that are all impacted by changes in the Earth’s surface.

Given the goal of mitigating climate change, it is important to consider our influence on all of the system components and to work toward a better representation of the full system. Present mitigation strategies focus on a single factor (greenhouse gas concentrations) and a single spatial scale (global average climate). While these provide a starting point for confronting climate change; climate change involves other factors and other scales. Humans and ecosystems reside in local climates, not in the global average climate.....

"Which actions then clearly help to prevent “dangerous anthropogenic interference in the climate system?” Reducing greenhouse gas emissions to stabilize or reduce greenhouse gas concentrations in the atmosphere and minimizing loss of existing forests, grasslands, and native ecosystems surely work to minimize human-induced climate change on all scales. We suggest that efforts to restore or mimic the structures and functions of native ecosystems will also generally be consistent with the desire to minimize the human impact on the climate system. And, there are many other environmental, economic, and social values that are important in land management choices. Recognition of the complexity of human-caused changes in climate should not be used as an excuse to avoid actions that will minimize our disturbance of the Earth’s environmental system and that will decrease vulnerability to environmental change and variability. Reductions in net greenhouse gas emissions!
  and land-surface change, for example, represent appropriate approaches to lessen our impact on the environment. Our hierarchy of approaches for integrating land surface changes into climate mitigation strategies offers a significant challenge for the further integration of science and public policy.”

http://blue.atmos.colostate.edu/publications/pdf/R-267.pdf
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