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Carbon dioxide (CO2) is a vital component in photosynthesis; the process plants and phytoplankton use to harness the Sun's energy. The resulting organic molecules support most life as we know it, all but some of the oldest types of life, extremophiles of the domain Archaea. CO2 also plays a significant role in the Earth's climate, a role that is not as clearly understood as we might think, after hearing it repeatedly being described as a greenhouse gas.

The current average amount of carbon dioxide in air is 0.038% or 380 parts per million on a per volume basis (ppmv). This can vary due to local events, downwind from slash and burn operations in a rainforest for example. But what is most significant are variations in CO2 levels that coincide repeatedly with global warming and cooling cycles, typically occurring over 70,000 year periods.

Scientists studying "fossil" air bubbles from ice core samples drilled in Antarctica have been able to obtain a continuous record of carbon dioxide levels for the past 400,000 years. That record shows CO2 levels ranging from 180 to 200 ppmv towards the end of periods of glaciation (ice ages) through to levels around 300 ppmv at the end of warmer, interglacial periods; a level that was reached in the middle of the Twentieth Century. Since then CO2 levels have continued increasing to the current 380 ppmv, a concentration level that the Earth has probably not seen for millions of years; possibly not since the emergence of multi-cellular life.

We are in an unprecedented situation, no-one really knows what impacts the current concentration might cause, let alone what will happen if carbon dioxide continues to rise at present rates. Yes, it is one of the gases known to have a "greenhouse" or warming effect on global temperature, but what other impacts might it have?

The world's amphibian population, such as frogs, has been decreasing rapidly in the last 10 to 20 years. Amphibians can breathe through their skins and are considered indicator species, being more quickly susceptible to negative environmental impacts. While some of their problems relate to diseases that have been spread accidentally by human transportation, could increasing CO2 levels also be contributing to the amphibian die-off?

It is not only the seemingly unstoppable and accelerating amount of CO2 being released by human industry, agriculture, land clearance and transportation that need concern us. The steppes of northern Eurasia and similar areas of Canada used to

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