One should consider more than the CO2 absoption benefit when contemplating the necessity of planting and maintaining trees. It cannot be denied that trees, however far from the equator, are beneficial for the shade they cast, the noise they filter (even when leafless in winter), the beauty they create while screening ugliness, the compost they produce, and the runoff they absorb. Plant a tree anywhere you can, but make sure it is the appropriate tree in size and type for the situation.

I really don't understand this.

I understand that during the winter the trees are not active in photosynthesis, so they would just absorb any incoming radiation, while in the tropics during the day, the trees are active in photosynthesis all year long. So, CO2 will only be absorbed during the warmer parts of the year.

Isn't this dependant on the type of tree involved, say deciduous vs conifer? As well as actual species?

And in the winter any tree is going to have minimal cooling due to water evaporation.

Having said all that, I could see how the tropical area trees can have a larger impact, but it still doesn't make it clear that boreal regions will warm the Earth. I think their model is flawed, and would like to see alot more evidence as support.

As a side note, on the movie "An Inconvenient Truth," Al Gore showed the study of CO2 levels and there was a yearly cycle of CO2. It was said this was because most of the land on Earth is above the equator, and during the northern winter most of the trees are then dormant, so CO2 goes up, then back down in the summer. So it seems that the Northern forests have a pretty big effect on CO2 levels.

Also any forest I've been in has been cooler than the surrounding area, especially cooler than a nearby city.

Again I think the modeling is flawed.

When looking at models it is important to realize that they usually can only demonstrate one aspect of a complex system. As I have said before (in a previous TH article on this publication) it is likely that planting trees will not have the effect we think- but it is an error to think we know how a forest will absorb CO2, our knowledge of the microbial and complex ecosystems of a forest are still developing- just a few weeks ago it was discovered that northern forests can sequester carbon for 100,000 years. Something this model does not seem to consider.

I think the author of the article has got it wrong, he says that trees planted in the north doesn't reduce CO2 but i think what the report is saying is that the trees doesnt help against global warming.

Trees planted far up north would reduce CO2 but wont reduce global warming since they are dark and absorb heat.
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Writer's note: You're correct... that was my mistake. I'll get it changed.

I recall hearing many times that there are more trees in what is currently the United States than there were when columbus "discovered" America. Is this true? I know it has no bearing on the facts about Climate Change or Global Warming, but I was just curious.

To be more to the point. Planting trees anywhere in the world does help fight global warming, it just doesn't help LOCAL warming. I live in central Spain, at 40 degree latitude. Planting trees here helps fight global warming by absorbing CO2 but will also increase local area annual average temperatures, basically by increasing local area winter temperatures - and I have no problem with this. Global warming in Spain is leading to excessive summer temperatures - and these are what are causing many of Spain's environmental problems, drought, forest fires, heat waves, water shortages. The trees help reduce local area temperatures in the summer. But the summer decreases do not offset the winter increases. If enough trees are planted in areas far from the equator, the increased local area annual temps would bump up the annual global average temps. I don't see this as a problem. Calculating numbers, I can see how it would lead to 'increases' in global annual average temps, but the tree planting far from the equator would still help fight the negative effects of global warming in Spain, and many other areas, and it would help fight global warming by sequestering CO2.

Worth noting: in the northern temperate zone, oxidation of dead plant matter slows and eventually halts as the freezing point is approached; hence while uptake of C02 decreases in trees, so do both respiration and decay. Conversely, in the tropics, decay proceeds all year. A good model must account for these rate changes per each ecotone. Use of a uniform rate all year grossly distorts the picture.

I've always wondered if planting trees could really help lessen global warming. The issue is the carbon cycle. The carbon in fossil fuels has been sequestered/removed from the cycle and stored underground. We then burn the fuel and put the carbon back into the cycle; planting trees to take it out of the air still keeps the carbon in the cycle, because trees are major players in regulation of carbon. It may take carbon out of the atmosphere but it will eventually go back when leaves rot, the trees die or burn up in a fire, or if we just start cutting them down to use for paper and lumber (which would eventually be burned or rot as we throw paper away and old houses need to be torn down).

I run a company (Treeflights) that plants trees (in GB) to absorb CO2 released by air travellers. This research potentially undermines my work. If it is proved to be correct , we will have to accept it however counter-intuitive it may feel. Having said that, it is a global model and so will never accurately predict temperature effects at a regional or local level. For example, the land we plant on is steep north facing pasture. The envisaged 'albedo warming effect' of forest canopy will be significantly reduced in this situation.
Darrin. If we put the trees in the sea after they mature, they may not relinquish their carbon to the atmosphere for a thousand years. We 've got this idea of a Sequestration Farm. On maturity the tree is harvested into big baulks and stored underwater. Another tree is planted in its place and the process repeated. (~10 times).
A tree anywhere is good. It may turn out that a tree in the tropics is better at fighting climate change than one in the north.

Adding to the topic of sequestration that Ru mentioned,
I have read of a form of sequestration in which carbon dioxide is stored in underground layers of sandstone in mid-western states which may effectively hold the carbon dioxide gases.
USA Today has an article found here

To Treeflights: keep doing good work. The way this research is being spun in the media is truly worrying. The "Duke experiment" just says that existing trees cannot rise to the occasion of elevated CO2 levels and absorb substantially more than usual. Now, why did anyone think they could? This is not such an earth-shattering discovery.

But this is now being spun as trees being "not good", being bad even! Right, let's cut the remaining forests in Europe and North America "to offset global warming". Leaves, you see, are slightly darker than grass... Does anyone in their sane mind buy this? Let's then turn Yellowstone into Death Valley, because sand reflects even more light.

Can you guess who is behind this spin?

The correct conclusion is that we need more trees, both in the North and the South. There is no other alternative. Trees do their job, we just need enough of them.

Mikhail

An obvious, shared experience:

In any situation, the temperature in the shade of a tree is cooler than it is out in the open.

Conclusions drawn from this study are dubious at best. We invite you to read our article on the subject:

http://ecopreservationsociety.wordpress.com/2008/02/12/does-reforestation-contribute-to-global-warming-a-second-look-at-the-livermore-study/

Planting trees helps “fighting a global warming” as much as postponing a sunrise by producing shadows.

However, trees sometimes adsorb pollution in general.

There are a number of problems with this study. I am not going to make the case as to whether trees in northern climates add/detract to global temperatures, rather I will take a careful look at the premises and methodology.

"forests can cool the planet by absorbing the greenhouse gas carbon dioxide during photosynthesis."
Well, maybe, but the study only shows that their computer model shows this. One methodology of modeling doesn't prove anything. Plus, the study probably makes quite a few assumptions that have not yet been proven.

"they can also cool the planet by evaporating water to the atmosphere and increasing cloudiness; a deck of white clouds reflects incoming solar radiation straight back out into space"
The study does not make a very compelling correlation. The amount of water vapor in the air is only ONE factor in the creation of cloud cover. What about other meteorological factors, and why weren't those taken into account? Also, water vapor comprises 92% of all greenhouse gas Why wasn't this factored?

"trees can also have a warming effect because they are dark and absorb a lot of sunlight, holding heat near ground level"
That is a gross generalization. Trees also cool surrounding air through transpiration, overcoming the absorptive and release affects of sunlight. Also, color is not the only important factor in retention of heat - material is also a factor. A green piece of asphalt releases heat differently than a green leaf.