Evidence of human-induced warming

• Global warming is a result of industrialisation
• Greenhouse gas concentrations have increased dramatically
• Measuring global warming
• Identifying the causes

Global warming is a result of industrialisation

Three facts combined explain why global warming is a result of industrialisation:

• the Earth has a natural greenhouse effect
• greenhouse gas concentrations have increased dramatically
• there is a strong relationship between global temperature and carbon dioxide levels

Greenhouse gas concentrations have increased dramatically

Concentrations of greenhouse gases in the atmosphere are much higher than they have been for the last 800,000 years.

Since industrialisation, greenhouse gas concentrations have increased dramatically.

The major cause of this increase is the burning of fossil fuels.

(Source: Climate change: the scientific basis for concern, MCV factsheet, 2008; PDF 1.3 MB)

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Measuring global warming

Many independent measures show that the surface of our planet is warming:

• temperature over land
• temperature over the oceans
• the rate of melting glaciers and sea ice
• the rate of sea-level rise
• the timing of flowering and ripening (these are happening earlier)
• the length of growing seasons (they are getting longer)
• the amount of coral bleaching
• migration of plants and animals towards the poles

Identifying the causes

Comparing what is actually happening with what climate models predict is the most practical and powerful method of assessing the likely causes of recent global warming.

These comparisons show that the global temperature over recent decades has increased much more than what we would expect from natural climate variability.

Various patterns of climate change provide important evidence for determining the cause of this large temperature change.

Observed patterns of change that are consistent with patterns of human-induced global warming include:

• greater warming at the poles compared to the equator
• greater warming over land compared to the ocean
• cooling in the upper atmosphere (stratosphere)
• oceans warming from the surface downwards
• greater warming at night
• greater warming in winter
• less rain in the sub-tropics
• changes in atmospheric pressure