The science of climate change and global warming

The massive and rapid change to our climate that we are now seeing is like nothing humankind has seen before. Consequently, the science around it has traditionally been cautious and careful in reaching consensus. But a strong consensus has now been reached; the scientific community agrees that climate change is real, it's caused by human activity and it's happening faster than anyone could have foreseen.

Emissions of greenhouse gases such as carbon dioxide and methane from burning fossil fuels and farming are causing global warming. This general warming of the earth's atmosphere is causing increasingly severe weather, desertification, melting icecaps and sea level rise, species extinction and the spread of disease.

We're seeing the effects of global warming all around us - more intense heat waves that disproportionately affect the elderly and poor, more severe storms that wreak havoc on homes and communities, and all kinds of changing cycles in the natural world. It is already costing large amounts of money; just look at the crippling effect of a prolonged drought on New Zealand farmers. The longer we leave the problem, the higher the cost.

The science

Global warming is occurring because we have upset the delicate balance of gases that traps heat in our atmosphere and allows life to exist as we know it. Simply put, a combination of carbon dioxide, methane and water vapour traps enough heat in our atmosphere to allow life to exist but we have upset the balance. We have introduced carbon dioxide, methane and nitrous oxide, into the atmosphere in massive amounts by burning fossil fuels, cutting down huge areas of forest and used farming methods that further add to the problem.

Now there is too much carbon dioxide, methane and nitrous oxide in the atmosphere; it now contains 32 per cent more carbon dioxide than it did in the mid 1800s. All these gases act like a planetary blanket retaining too much of the sun's heat. That means we are fundamentally changing our planet's climate. The northern hemisphere is now warmer than any point in the last one thousand years.