Mmm, not good. So far I've heard about more hornets (as the warmer winters allow more hornets to survive) and more poison ivy. Man, global warming really sucks.

Aren't there any positive effects like, say, larger marijuana plants?

Seriously? Oh no. Bad CO2, bad. Has anybody been to the fourth grade at some point in their life? All plants breathe CO2 and create oxygen. All plants do better when there is more CO2. More CO2 equals more apples, oranges, poison ivy, trees, weeds, and the rest.

By the way, you exhale CO2. Don't support taxing CO2 (it's goes against all common sense).

Positives? as CO2 is plant food, I would expect Larger plants all the way around, including crops.
With larger wasps they can perhaps lay more eggs in more caterpilers killing more bugs so we need to use less pestacide.

Won't all plants grow larger with increased CO2?

Perhaps you've forgotten, or else never read the TH article regarding USDA findings that CO2 may create "super-weeds" that may be able to compete more aggressively against cultivated plants (you know, like corn and wheat and other nifty major edible food crops).

Here's the link:

http://www.treehugger.com/files/2008/06/usda-climate-change-super-weeds.php

That is a terribly punctuated and worded title.

We all know that more CO2 makes almost all plants grow better and have better yields; which of course includes poison ivy. How is this news?

Hey people and there is a use efor poisen ivy. this is a guess but ive done lots of research and welll poisen ivy takes in a bit more co2 then any other plant and theres tomuchCO2 in the air so there for if scientist could get preservatories of this plant then more CO2 would go down at a faster rate ive done a terrarium expirement with it and it worked so idk mabye its true mabye not but thats science.