You've got it backwards. Rain forests are bad for climate change, not good. Chopping down a rain forest to replace it with agriculture gives you far better sequestration (trees rot, releasing methane; food is processed into landfills) and the lighter colored agricultural products reflect sunlight rather than absorb it like trees do. Inarguably a rain forest is better than a parking lot. But no one is cutting down rain forests to build parking lots in Brazil.

But I had to check. You don't actually believe this do you?

Your assertion is laughably wrong.

Rainforests can easily sequester ~5000 tons of CO2/acre, or more. Agriculture is a very significant contribution to greenhouse gasses - 12.5% - even before considering the land use (from forest sequestration to industrial farming - which is responsible for another 10% of the annual greenhouse gas contributions).

Biofuels studies have shown that it would take up to 3 centuries for biofuels production on an acre that was once forest to "pay back" the carbon that was released in converting that forest into farmland.

As far as environmental concerns go: Forests are good, agriculture is bad... and your assertion is VERY wrong.

;)

sorry xando, I think you've got that backwards.

Xando, your statement seems contrary to everything I have heard or read. Do you have any evidence to support it?

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Aren't most rainforests in the tropics?

No pejoritive intended towards you (unless you helped author that particular study), but that is a FOOL's "study".

There's a lot of misguided blather out there showing an incredible lack of understanding on the part of so-called "experts".

Here we have an idiot with a PhD that lacks a fundamental understanding of the difference between local effects and global effects.

Light absorbtion is a local effect. If you pave a sq mile with black tar, then that 1 mile area will be warmer due to greater absorbtion of energy.. but there's nothing added to the ATMOSPHERE keeping that energy locked in... which means that it will diffuse and gradually radiate back into space at a constant gradient. So local effects of forests MIGHT (I'm skeptical) have some different effects concerning light absorbtion... but that isn't important. That would only effect the local temperature of the immediate region that the forest is covering. We aren't worried about the exact temperature measured on someone's thermometer... we're worried about global climate change.

CO2 emissions have a global effect, because that serves as insulation for the planet... which means that whatever heat is absorbed by light does not radiate back out into space, or at least not as efficiently. The two issues are so vastly different as to be unrelated.

The only place where light absorbtion matters is ice sheets and glaciers: glacers because increased absorbtion of energy leads to higher melt rates, which leads to the loss of spring meltwater for hundreds of millions of people... and ice sheets because increased absorbtion of energy in the arctic waters and over ice sheets results in more rapid ice-sheet movement and calving - which leads to rising oceans.

High latitude forests MAY result in a very slight local increase in light absorbtion - in the winter - leading to slightly higher local temperatures (though the link you provided said this is only true in high latitudes, and specifically stated that tropical forests have temperature reducing effects...), but those local effects will diffuse LONG before they could effect Greenland, or the Himilayan glaciers. However, cutting down a high latitude forest will result in the release of billions of tons of CO2 - which will absolutely effect global energy insulation effects and WILL result in higher melt rates for Greenland ice sheets, and greater desertification of inland plains, and greater storm energy, etc... While planting new forests absolutely will pull millions of tons/year OUT of the atmosphere, which will partially mitigate the increasing insulation of the atmosphere... ... ...

Hi Tundra,

For once I think you are wrong. Albedo changes do have a significant effect and are typically considered one of the feedbacks causing the the onsets and ends of ice ages. The authors used standard GCM's to predict the size of the impacts. Now, if I'm reading the second to last paragraph correctly, the authors predict that the C02 radiative forcing would outweigh the albedo effects for about 80 years (after which enough C02 is drawn into the deep oceans and rocks). The Guardian write up didn't make that clear. Surprise!

The other issue is that it is not a comparison of converting between forest and grassland but of the difference between the two initial conditions. Current agricultural practices, mainly tilling, release about half of the carbon stored in the soil. So, as you know, converting to agricultural use incurs a large carbon debt.

The oceans are the world's heat sink... so energy that is absorbed by the ocean doesn't and won't be quickly radiated back into space. A warming ocean is clearly a major issue with regard to global climate change, especially with respect to ice sheet melt rates... but it also has a huge effect on the trade winds, which affect all global weather patterns.

On land, however, I am not the least bit concerned whether a few million square miles of central Asia have a 1 degree average difference or not (this would largely be a result of a warmer winter and night, offsetting a cooler day and summer... with the major annual difference being a lessoning of snow cover for however long the area would normally see snow). Add to this the fact that the big boogeyman for global warming - with respect to the continental interiors, is desertification... something that forests specifically help protect the land from.

My response to Xando was only regarding Albedo changes on land, not overall. Over water, a wonderful thermal storage medium, that's a completely different issue. However, I don't know of any forests grown over the seas, so I didn't think that was a necessary caveat.

:)

You're right, of course, about the agricultural issues. That carbon debt is FAR FAR FAR larger when converting an existing forest into agriculture, because of the thousands of tons/acre of CO2 that are sequestered as trees.

But the authors of the study weren't advocating burning forests down in order to make more farmland... they were just trying to prevent reforestation efforts from recieving carbon offset money. I disagree with them quite vehemently... but I am the first to mock people when they assert that the world could be saved through the planting of the magic forests (we'd need most of land area of the world to be planted)... but I do strongly believe that reforestation would have some cost-efficient mitigation effects. It's just limited in the potential scope to a few percent of the problem.