[Refractor (OP)]

Is it possible that increased levels of carbon dioxide in the atmosphere will boost growth rates or in some way benefit some or all plants, or algae?

[blakestyger]

Yes. This very thing has been put into action by British Sugar plc at their Wissington factory in Norfolk (UK). The factory has built eleven hectares of glass houses that utilise waste carbon dioxide from the CHP boilers to grow 70 million tomatoes each year, 10% of the home grown tomatoes in the UK. 

[Make it Lady]

Why do you think talking to plants is good for them? It is the CO2 in your breath. You would really have to do a lot of talking to do any good though. My Mum had a very abundant plant in the hall by the phone. She does go on a bit!!!!