Gore / Carbon sink

A Question for Mr. Gore:

So, by now we've all heard about Gore's gigantic house, and his likewise gigantic electrical bill. (If you haven't, see here and its supporting links). The defense is, essentially, that Gore is "carbon neutral" by using services that plant trees for him, offsetting his power usage.

So my question is: What about this?

Although the United States and Canada produce a substantial amount of industrial carbon dioxide emissions, a new study contends that the North American continent is a net carbon sink whose vegetation may be absorbing the entire annual emissions of the two countries.... Fan attributes the North American sink to four factors:

* U.S. forests are being replenished, in part by new methods of feeding livestock brought on by a growing demand for meat. For example, during the last century hogs and cattle were permitted to wander the mountainous areas of the eastern United States. Today, however, such animals are restricted to concentrated areas like feed lots.

* Air in the Northern Hemisphere is rich in nitrogen (a plant food), thanks to the area’s industry and agriculture. Science reported in 1992 that nitrogen fertilization was stimulating European forests in the same manner and surmised that China and tropical rain forests were sure to follow this trend.

* Increased amounts of CO2 increase photosynthesis and water-use efficiency.

* Satellite data indicate a lengthening of the growing season in the highest latitudes.

The last one is ironic: global warming from greenhouse gases yields longer growing seasons for agriculture, which in theory reduce global warming by greenhouse gases.

But as to the larger question: if North America is a carbon sink, does that mean we can just carry on like this forever? If it's good enough for Al Gore, why shouldn't we do just as we like also? We're planting trees too -- lots of them.