People & Planet - The Science of Climate Change

“There is new and stronger evidence that most of the warming observed over the last fifty years is attributable to human activities” Intergovernmental Panel on Climate Change (IPCC) 2001 report.

The world’s climate is changing dramatically after nearly 10,000 years of relative stability, as a direct result of our lifestyles, and in a way that threatens to destroy them forever.

Page contents:

The natural cycle
How human activities are changing ourclimate

1. The natural cycle

Our weather systems and temperature levels are determined by the interaction of factors such as the sun’s rays and ocean currents. However, it is the ‘greenhouse effect’ caused by naturally occurring gases in the atmosphere which keeps global temperatures, and hence our weather stable.

The sun’s rays hit the earth. They are absorbed by its surface, warming our land and oceans, and then re-emitted back into space. If all this energy simply escaped, the earth would be around 30°C cooler, and humans wouldn’t be here! However, naturally occurring gases such as carbon dioxide, water vapour and methane form a thin protective ‘greenhouse’ around the earth, trapping enough of the energy to gently heat the atmosphere before it escapes. This insulates the earth, giving us warmth.

This warming blanket been sustaining life on earth for millions of years, with our climate varying only with natural occurrences.

This stable balance is changing fast.

See

2. How human activities are changing our climate

Since the industrial revolution about 200 years ago, we have been using ever increasing amounts of fossil fuels — oil, coal and gas. The burning of these fuels, mainly oil and gas for transport and industry, releases huge levels of carbon dioxide (CO₂) into the atmosphere. This has led to a 30% increase in atmospheric CO₂ levels over the past two centuries. Today, we are releasing about 6.5 billion tonnes a year of CO₂, more than ever before, and thus dramatically changing the composition of the atmosphere. The concentration of CO₂ in the atmosphere is measured in PPMV (parts per million volume), and has increased from approximately 270 PPMV to 370 PPMV since the industrial revolution. CO₂ also lasts for up to 100 years in the atmosphere.

Global atmospheric concentration of CO₂
Full-size image available at: Vital Climate Graphics: Introduction to climate change

Credit: United Nations EnvironmentProgramme & GRID-Arendal

In addition, intensive cattle rearing and rice planting to feed western appetites for cheap produce has massively increased the amount of methane emitted annually, and as this natural greenhouse gas is more potent than CO₂, despite much smaller volume of emissions, it also has a significant warming effect

For more about CO₂ and its effects, see:

When combined with the 1% of our forests being destroyed each year for industry, releasing more CO₂ and reducing our ability to convert excess CO₂ into oxygen, the effect is to dramatically thicken the ‘greenhouse’ around the earth, to the point where more energy is trapped, unable to escape thus heating the atmosphere.

This build up of greenhouse gases due to human activity causes the effect usually called global warming. Most people assume it will simply cause a rise in temperatures. However, it is better to call it climate change, as its dangerous effects may be more complex.

See:

For an interactive guide, see:

For an introductory FAQ, see:

IEAGHG: CommonQuestions about Climate Change

For the scientific basis in depth:

For predictions of the effect this will have on the climate system, go to:

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