Question 2:

Is the Earth's climate really hotting up?

The global average surface temperature has increased since reliable measurements began in the late 1800s.

During the past 100 years, global average surface temperature increased by about 0.7°C. Tree rings and other records tell us that average Northern Hemisphere temperatures during the second half of the 20th century were likely to have been the highest in at least the past 1300 years. Eleven of the past 12 years were the warmest we have experienced since around 1860.

In addition to warming of the Earth's surface, there has been an increase in heatwaves, warming of the lower atmosphere and deep oceans, fewer frosts, retreat of glaciers and sea ice and a rise in sea level during the 20th century of approximately 17 cm. Many species of plants and animals have changed their location or the timing of seasonal activities in ways that provide further evidence of climate change.

Although many natural factors influence the Earth's climate, a majority of the world's scientists have determined that greenhouse gas increases were the main factor contributing to climate change since the 1950s.

In its Fourth Assessment Report released in 2007, the Intergovernmental Panel on Climate Change - an international body that assesses the latest science of climate change - stated that ‘Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in [human produced] greenhouse gas concentrations”.

Scientists consider that warming will continue as a result of past, current and future emissions. Question 15 addresses how much warming is likely this century.

Earth's Temperature 1000-2100

This graph indicates how the Earth's surface temperature has increased since the mid 19th century. Scientists have projected a range of possible temperatures based on a number of future greenhouse gas emission scenarios. Scientists believe that the Earth's average temperature will rise by 1.1 to 6.4°C by 2100 if nations around the world do not act to control greenhouse emissions.

This graph has been adapted and simplified from the Intergovernmental Panel on Climate Change Third Assessment Report 2001. The original graph can be accessed at: www.ipcc.ch/