Climate change summary

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What is climate change?

Climate change is the long-term change in average weather conditions, including temperature, precipitation and wind.

According to the United Nations Intergovernmental Panel on Climate Change (IPCC), which is comprised of the world’s leading scientific experts in the field of climate change, the global climate is undergoing dramatic changes as the direct result of greenhouse gas emissions from human activity. Climate change is already apparent as evidenced by higher temperatures, rising sea levels, increased ocean acidity and ice melt. Global surface temperatures, alone, have increased by roughly 0.74 °C (1.33 °F) between the start and the end of the 20th century. According to the IPCC these trends are set to continue to accelerate into the 21st century and will be accompanied by new changes such as increases in extreme weather events like hurricanes. In fact, according to the IPCC’s latest findings, global average temperatures will probably rise a further 1.1 to 6.4 ºC (2.0 to 11.5 ºF) this century, depending on the extent of continued greenhouse gas emissions.

What are greenhouse gases (GHGs)?

Greenhouse gases are gases in the atmosphere that act like a blanket or glass roof around the earth, trapping in heat that would otherwise escape to space – this is commonly referred to as the “greenhouse effect”. From the end of the last Ice Age about 10,000 years ago to the end of the 18th century, the levels of greenhouse gases in the atmosphere remained fairly constant and at a level sufficient to sustain life as we know it today. Since the Industrial Revolution 200 years ago, mankind has been releasing unprecedented amounts of greenhouse gases into the atmosphere, which trap more heat, amplifying the natural greenhouse effect.

Carbon dioxide (CO2) is the most significant greenhouse gas released by human activities and is emitted mostly from the burning of fossil fuels like coal, oil and natural gas. Other greenhouse gases include methane and nitrous oxide.

How do we know that climate change is real?

As early as 1995, the IPCC had strong scientific evidence that climate change was occurring and that human activities were a primary cause. Since then, the IPCC has conducted four detailed assessments of climate change which on each occasion has reported greater confidence in the case for human-induced climate change. By 2007, the IPCC concluded that it is ‘‘extremely unlikely that the global climate changes of the past fifty years can be explained without invoking human activities’’. Prominent scientists and major scientific organisations have all ratified the IPCC conclusion. Today, all but a tiny handful of climate scientists are convinced that earth’s climate is heating up and that human activities are a significant cause.

The scientific consensus regarding climate change is based on the work of thousands of experts from hundreds of research institutions located across the globe. Scientists worldwide have considered all the possible natural factors that affect climate on Earth, from the output of the sun to the effects of volcanoes. After analysing the possible impacts on both warming and cooling of each of the factors, along with man-made factors, the IPCC concluded that most of the observed increase in globally averaged temperatures since the 1950s is very likely (more than 90% certainty) due to the observed increase in man-made greenhouse gas concentrations over the same period.

What are the potential consequences of climate change?

Without effective action to halt the rise and then reduce the levels of greenhouse gases released by human activity, countries worldwide and their citizens face a bleak future.

There will be increased disruption to society from extreme weather, with more frequent storms and flooding, more severe droughts and heat waves; rising sea levels and thawing permafrost will put essential infrastructure under pressure; in many regions agriculture will be adversely affected by water shortages and extreme heat; the effects on the natural world will also be severe with the loss of coral reefs as oceans warm and of tropical forests as fires become more frequent.

These impacts will be felt in economic terms and the pressure on already stressed world financial systems could be catastrophic. There will also be social consequences with mass human migrations from lands affected by drought and famine and extreme heat stress in the urban areas of topical and subtropical countries.

Can climate change be reversed?

Some changes to our climate are inevitable given the historic build up of emissions in the atmosphere, but immediate action is needed to avert the worst of these impacts.

According to recent calculations by the IPCC, the level of action required is considerable. It is estimated that greenhouse gas emissions would need to be cut by at least 80% by 2050 in order to avoid the worst impacts of climate change. Some countries, like the UK, have committed to reducing their greenhouse gas emissions in line with this target however most countries still have not. The more action is delayed the more the levels of greenhouse gases will rise before they are brought under control, committing the Earth to greater levels of warming and making the required reductions even greater.

Fortunately, many technological solutions exist for reducing greenhouse gas emissions. While these technologies come with a price, it is far outweighed by the cost of inaction. Financing these technologies, however, remains a challenge. New sources of finance, such as the carbon markets, are required to mobilise the necessary investment and financial flows to address climate change.