Global warming has also had an impact, with changing patterns of natural vegetation and more profuse pollen production.

This resulted in increasing forest density and aging trees, further contributing to pollen production and thus, hay fever.

Specifies of pollen production, dissemination and pollination are not known.

Colder air discourages pollen production.

The scientists identified the specific plant gene involved in activating a cell that makes a substance needed for pollen production.

Introducing this construct into a plant turned off the pollen production.

Ragweed is a plant of concern in the global warming issue, because tests have shown that higher levels of carbon dioxide will greatly increase pollen production.

The mutations cause the breakdown of the mitochondria in these specific cells and result in cell death and so pollen production is interrupted.

The analysis involved summer temperatures, since that is when the climatic record as reflected in tree rings, pollen production and ice melting is clearest.

Global warming has a "direct" effect on respiratory illnesses because increased CO levels stimulate pollen production, which stimulates allergies.