[Dace]

If i were you i'd do the talk with the following topics

WHAT IS CLIMATE CHANGE?

This is your introduction. Talk basically about the Earth and the weather. Effect of the sun (heating the equator) causing wind and the transfer of heat causing ocean currents etc. Mention the fact that there have been changes in the climate of earth in the past (what were they) and the belief held by the scientific community that we are about to undergo another change.

WHAT CAUSES CLIMATE CHANGE?

What has caused climate change in the past:
Volcanic erruptions
Sun spot cycle
etc
What is causing climate change at the moment:
Mention ozone layer, fosil fuel burning, deforestation etc

Also mention "feedback mechanisms" such as:
* Polar ice melting / heavy rainfall in Europe increases fresh water supply to the ocean current system running from the equator in America to Northern Europe (whose name i can't remember at the moment).
* Increased temperature in the tundra (siberia) is leading to the melting of the permafrost which has a further effect. The methane stored underneath the permafrost escapes (methane is a "bad" gas with respect to global warming ... worse than CO2) and there's massive amounts of it.
* Increased temperatures (Spring has advance a day per year for the past decade or so in Siberia or Canada or something) which has affected the breeding pattern of some insect in the north which used to only breed every two years but now breeds every year. As such there's mass infestations (plagues) of these creatures. As they need to eat they are stripping the leaves from the trees in the north. Without leaves the trees die creating "dead land" which as it is darker than land with trees on it attracts more heat further fueling the problem of climate change.

WHAT ARE THE EFFECTS OF CLIMATE CHANGE GOING TO BE?

* Temperature changes (most places getting hotter ... the equator will become uninhabitable)
* Weather changes (predicted increases in the number and general strength of hurricanes etc)
* Flooding (the ice caps melt and the water rises ... show a general world map of areas affected noting the number of displaced people especially in areas like Bangladesh ... then show a "revised map of the UK" ... you might want to ask people if they have any relatives who live in areas projected to be under water)
* Loss of biodiversity
* Economic effect of all this (including effect on stockmarket and thus on pensions etc ... in short this will affect everyone)

WHAT CAN I DO TO HELP AVERT CLIMATE CHANGE?

The biggest polluters are Industry so you would have to pressure the Government to make any changes. Tell your audience how you can do this.

End on a positive note by stating the small changes people can make i.e. recycling, not wasting energy etc.