The Earths climate undergoes a wide range of natural variation over time. However, the vast majority of the world's climate scientists agree that the climate is now undergoing rapid changes, and that human activity is a key agent in driving this change.

The earth is kept warm by the greenhouse effect, when gases in the atmosphere trap heat from the sun that is being reradiated back into space from the earth. Adding more greenhouse gases (GHG's) to the atmosphere increases the amount of heat trapped, forcing global temperatures to rise.

The key issues associated with climate change are:

1. Current changes are being forced by human activity

There are two main ways our actions influence the climate:

1. Releasing GHG's into the atmosphere from burning fossil fuels and from clearing vegetation (carbon is released from decaying vegetation and associated soils)
2. Reducing the removal of carbon dioxide (CO₂)the principal GHG, as a result of vegetation clearing associated with land use changes.Currently approximately 8 000 000 000 tons of CO₂ are released into the atmosphere every year from burning fossil fuels (approx 6.4Gt CO₂) and land use changes (1.6Gt CO₂) – IPCC, 2007:Summary for Policymakers. Atmospheric carbon dioxide levels are currently higher than at any other time in the past 420 000 years.

The good news here is that by changing our actions we can reduce the extent of climate change.

2. The rate of Change

We have already observed changes to our climate that are more rapid than anything the earth has experienced for at least the last 1 800 years (CSIRO- www.csiro.au/resources/psrs.html). Warming over the past 50 years has been twice that of the last 100 years, and 11 of the last 12 years (1995 - 2006) rank amongst the hottest on record (IPCC, 2007:Summary for Policymakers).

The changes that are occurring are happening very rapidly.This has big implications for animals and plants and the ecosystems of which they are part as most will struggle to adapt to such rapid changes, and many will go extinct with flow on implications for the health and stability of the environments of which they are a part.The pace of change also has big implications for humans, as it will impact agriculture, habitability of coastal areas, human health and spread of diseases, water availability and many other facets of our lives.

3. Small changes in temperature have big consequences.

The earth has warmed, on average, by about 0.7 °C since 1910 (for Australia it has been a 0.9°Crise - CSIRO). Over the next 90 years, global average surface temperatures are expected to increase between 1.4 to 5.8°C (IPCC). These figures don't sound very big, but if you consider that arise in temperatures of 1.5-2.5^oC is likely to result in 20-30% of all known plant and animal species being at an increased risk of extinction (IPCC Climate Change 2007:Impacts, Adaptation and Vulnerability), one starts to get a sense of the magnitude of what appear to be small changes in temperature.Both the Great Barrier Reef and upland Wet Tropics Rainforests are highly sensitive to increases in temperature, and an increase of 2 degrees will result in major species declines in both these world heritage environments.

4. It's the extremes the count

Small increases in temperature result in larger climate variability and greater extremes, and it is usually the extremes that do the damage. For example, elevated temperatures of 1 deg C above the long term monthly summer average are enough to cause coral bleaching in many dominant coral species (GBRMPA). Whist this may occur for only a couple of weeks each year, if it happens every year, reefs don't get a chance to recover, die and get replaced by algae.It only took a few extreme days of heat to result in the premature death of approximately 70 000 people in the European heat wave of 2003.

5. Dangerous Climate Change

A 2°C increase in global average temperature (or around 450 ppm CO₂) is considered by many to denote the threshold for dangerous climate change – i.e. the point at which the climate system may move to a state that we no longer have any great ability to influence change.The climate is a non-linear system, which means it has tipping points which if crossed will shift the system rapidly into a new state.We don't know exactly where these tipping points are, but many climate scientists are deeply concerned that we are now dangerously close to one, and there is strong agreement that we need to stabiles the climate at or below 2°C to avoid the possibility of crossing such thresholds.A 2°C increase in temperature will already result in major changes to weather systems across the worlds and have major negative impacts on the environment and communities alike.

     F. Slow response time

Carbon dioxide remains in the atmosphere for an average of about 80 years.This means it takes a number of decades for the climate to respond to changes we make today.We know we are dangerously close to causing major disruptions to the global climate, so it is therefore essential that strong action be taken sooner rather than later, given this slow response time. Even with immediate action to reduce our GHG emissions, this slow response time also means we are going to experience some degree of climate change.The longer we leave action to address this, the more sever these changes are likely to be.

    G. We have the tools and technology to tackle the issue now

The changes required to tackle climate change are changes that already make social, economic and environmental sense. We can effect major reductions in greenhouse gases by dramatically improving efficiency, replacing fossil fuels with renewable energy, and making sure our activities are sustainable.If we are to avoidmajor climate change, we need to reduce our emissions dramatically over the next one to two decades – this is achievable using current technologies,but requires considerable community support and political will.