What is climate change?

Persistent human activities like driving cars, farming, burning coal and cutting down forests produce greenhouse gases – mainly carbon dioxide, methane and nitrous oxide. These gases gather in the atmosphere, wrap around the earth and trap the sun's heat.

The more greenhouse gases we emit, the faster the world's climate heats up. This process is often called ‘global warming’ but it is better to think of it as ‘climate change’ because it is likely to bring about more extreme events – floods, storms, cyclones, droughts and landslips – rather than an increase in temperature alone. Climate change could have significant impacts on our economy, environment and the way we live – the effects of a warming planet and subsequent changing climate patterns are already becoming evident.

Globe and greenhouse gases.

 

The Earth has gone through massive changes in its 4.5 billion-year history. Its climate has naturally fluctuated between being very cold and covered in ice, or very hot. In the past 10,000 years the planet’s climate has become much more stable, leading to flourishing flora and fauna, and the subsequent population explosion of humankind.

However, over the past 50-100 years, increasing industrialisation and human activity (such as industry, agriculture and transportation) have begun to affect the natural climate balance. These activities are increasing the amount of greenhouse gases in our atmosphere and causing Earth not only to heat up, but to heat up at an unprecedented rate.

Since the start of the industrial revolution (about 1750) the overall effect of human activities on the climate has been a warming influence. The human impact of this era greatly exceeds that due to known changes in natural processes such as solar changes and volcanic eruptions.

Scientists are now detecting changes which suggest the climate is becoming hotter on average, and more variable. This variability is being attributed in part to increased levels of carbon dioxide in the Earth’s atmosphere. According to scientific studies, in the past 650,000 years the planet has never had so much carbon dioxide in its atmosphere as it does today, and the levels are continuing to rise.

Concentrations of greenhouse gases from 0 to 2005

The graph shows atmospheric concentrations of important long-lived greenhouse gases over the past 2000 years. Increases since about 1750 are attributed to human activities since the industrial era.

The graph shows atmospheric concentrations of important long-lived greenhouse gases over the past 2000 years. Increases since about 1750 are attributed to human activities since the industrial era. Credit: Graph courtesy of the IPCC.

Climate scientists expect the Earth’s average temperature will increase by between 1.1 and 6.4°C this century. In New Zealand, average temperatures are projected to increase about 1°C by around 2040 and about 2°C by around 2090.

The United Nations Framework Convention on Climate Change (UNFCCC) defines “climate change” as “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”. The UNFCCC thus makes a distinction between “climate change” attributable to human activities altering the atmospheric composition, and “climate variability” attributable to natural causes.